1Vectors_params(3NCARG)           NCAR GRAPHICS          Vectors_params(3NCARG)
2
3
4

NAME

6       Vectors_params - This document briefly describes all Vectors internal
7       parameters.
8

DESCRIPTION

10       Parameter descriptions follow, in alphabetical order. Each description
11       begins with a line giving the three-character mnemonic name of the
12       parameter, the phrase for which the mnemonic stands, the intrinsic type
13       of the parameter, and an indication of whether or not it is an array.
14
15       ACM - Arrow Color Mode - Integer
16
17              ACM controls how color is applied to filled vector arrows. It
18              applies only when AST has the value 1. Its behavior also depends
19              on the setting of the parameter CTV. Assuming that CTV is set to
20              a non-zero value, implying that multi-colored vectors are
21              desired, ACM has the following settings:
22
23
24
25              Value   Effect
26              -----   ------
27              -2      Multi-colored fill; outline off
28              -1      Fill off; multi-colored outline
29              0       Multi-colored fill; mono-colored outline
30              1       Mono-colored fill; multi-colored outline
31              2       Multi-colored fill; multi-colored outline
32
33              Mono-colored outlines use the current GKS polyline color index.
34              Mono-colored fill uses the current GKS fill color index. When
35              CTV is set to 0, both the fill and the outlines become mono-
36              colored, and therefore only modes -2, -1, and 0 remain
37              distinguishable. The default value is 0.
38
39       AFO - Arrow Fill Over Arrow Lines - Integer
40              If AFO is set to 1, the perimeter outline of a filled vector
41              arrow is drawn first, underneath the fill. In this case, you
42              must set the line thickness parameter (LWD) to a value greater
43              than unity in order for the line to appear completely. The
44              advantage of drawing the line underneath is that the full extent
45              of the fill appears, resulting in a crisper, more sharply
46              defined arrow; when the line is drawn on top of the fill using a
47              different color index, the fill color may be partially or
48              completely obscured, especially for small vector arrows. AFO has
49              an effect only when the parameter AST is set to 1.  The default
50              value of AFO is 1.
51
52       AIR - Arrow Interior Reference Fraction  - Real
53              AIR specifies the distance from the point of the arrowhead of a
54              filled vector arrow drawn at the reference length to the point
55              where the arrowhead joins with the line extending to the tail of
56              the arrow. Its value represents a fraction of the reference
57              length.  This distance is adjusted proportionally to the X
58              component of the arrowhead size for vector arrows whose length
59              differs from the reference length.  See VRL for an explanation
60              of how the reference length is determined.  AIR has an effect
61              only when AST is set to 1. AIR is allowed to vary between 0.0
62              and 1.0 and its default value is 0.33.
63
64       AMN - Arrow Head Minimum Size - Real
65              Specifies a minimum length for the two lines representing the
66              point of the vector arrow head, as a fraction of the viewport
67              width. AMN has an effect only for line-drawn vector arrows
68              (parameter AST set to 0). Normally the arrow head size is scaled
69              proportionally to the length of the vector. This parameter
70              allows you to ensure that the arrow head will remain
71              recognizable even for very short vectors. Note that you can
72              cause all the arrowheads in the plot to be drawn at the same
73              size if you set AMN and AMX to the same value. If you set both
74              AMN and AMX to 0.0 the arrowheads will not be drawn at all.  The
75              default value is 0.005.
76
77       AMX - Arrow Head Maximum Size - Real
78              Specifies a maximum length for the two lines representing the
79              point of the vector arrow head, as a fraction of the viewport
80              width.  AMX has an effect only for line-drawn vector arrows
81              (parameter AST set to 0). Normally the arrow head is scaled
82              proportionally to the length of the vector. This parameter
83              allows you to ensure that the arrow heads do not become
84              excessively large for high magnitude vectors. Note that you can
85              cause all the arrowheads in the plot to be drawn at the same
86              size if you set AMN and AMX to the same value. If you set both
87              AMN and AMX to 0.0 the arrowheads will not be drawn at all. The
88              default value is 0.05.
89
90       AST - Arrow Style - Integer
91
92              If AST is set to 0, the vector arrows are drawn using lines
93              only. When AST is set to 1, the vectors are plotted using
94              variable width filled arrows, with an optional outline. If AST
95              is set to 2, wind barb glyphs are used to represent the
96              vectors.There are parameters for controlling the appearance of
97              each style. These have an effect only for one value of AST.
98              However, certain parameters apply to all arrow styles. Here is a
99              table of parameters that affect the appearance of vectors and
100              how their behavior is affected by the setting of AST:
101
102
103              Parameter   Line-Drawn Arrows   Filled Arrows   Wind Barbs
104              ---------   -----------------   -------------   ----------
105              ACM                             x
106              AFO                             x
107              AIR                             x
108              AMN         x
109              AMX         x
110              AWF                             x
111              AWR                             x
112              AXF                             x
113              AXR                             x
114              AYF                             x
115              AYR                             x
116              CLR         x                   x               x
117              CTV         x                   x               x
118              LWD         x                   x               x
119              NLV         x                   x               x
120              PAI         x                   x               x
121              TVL         x                   x               x
122              WBA                                             x
123              WBC                                             x
124              WBD                                             x
125              WBS                                             x
126              WBT                                             x
127
128              When filled arrows are used, colors associated with the
129              threshold levels may be applied to either or both the fill or
130              the outline of the arrow.  When fill is drawn over the outline
131              (AFO set to 1), LWD should be set to a value greater than 1.0 in
132              order for the outline to be fully visible.  The default value of
133              AST is 0.
134
135       AWF - Arrow Width Fractional Minimum - Real
136              AWF specifies the width of a filled arrow drawn at the minimum
137              length, as a fraction of the width of an arrow drawn at the
138              reference length. If AWF has the value 0.0, then the ratio of
139              the arrow width to the arrow length will be constant for all
140              arrows in the plot.  If given the value 1.0, the width will
141              itself be constant for all arrows in the plot, regardless of
142              length. See VFR for a discussion of how the minimum length is
143              determined. AWF has an effect only when AST is set to 1.  AWF is
144              allowed to vary between 0.0 and 1.0 and its default value is
145              0.0.
146
147       AWR - Arrow Width Reference Fraction - Real
148              AWR specifies the width of a filled vector arrow drawn at the
149              reference length, as a fraction of the reference length.  See
150              VRL for an explanation of how the reference length is
151              determined.  AWR has an effect only when AST is set to 1. AWR is
152              allowed to vary between 0.0 and 1.0 and its default value is
153              0.03.
154
155       AXF - Arrow X-Coord Fractional Minimum - Real
156              AXF specifies the X component of the head of a filled vector
157              arrow drawn at the minimum length, as a fraction of the X
158              component of the head of an arrow drawn at the reference length.
159              The X component of the arrowhead is the distance from the point
160              of the arrowhead to a point along the centerline of the arrow
161              perpendicular the arrowhead´s rear tips. If AXF has the value
162              0.0, then the ratio of the X component of the arrowhead size to
163              the arrow length will be constant for all vectors in the plot.
164              If given the value 1.0, the arrowhead X component will itself be
165              constant for all arrows in the plot, regardless of their length.
166              See VRL for an explanation of how the reference length is
167              determined.  AXF has an effect only when AST is set to 1. AXF is
168              allowed to vary between 0.0 and 1.0 and its default value is
169              0.0.
170
171       AXR - Arrow X-Coord Reference Fraction - Real
172              AXR specifies the X component of the head of a filled vector
173              arrow drawn at the reference length, as a fraction of reference
174              length. The X component of the arrowhead is the distance from
175              the point of the arrowhead to a point along the centerline of
176              the arrow perpendicular the arrowhead´s rear tips.  See VRL for
177              an explanation of how the reference length is determined.  AXR
178              has an effect only when AST is set to 1. AXR is allowed to vary
179              between 0.0 and 2.0 and its default value is 0.36.
180
181       AYF - Arrow Y-Coord Fractional Minimum - Real
182              The value of this parameter, when added to the minimum width
183              value, specifies the Y component length of the arrowhead size
184              for a filled arrow drawn at the minimum length, as a fraction of
185              the length specified by AYF. If given the value 1.0, the
186              arrowhead Y component will extend the same distance
187              perpendicularly from the edge of all arrows in the plot,
188              regardless of their length and width. This can be a useful
189              resource to adjust to ensure that the points of even very short
190              vector arrows remain visible. See VFR for a discussion of how
191              the minimum length is determined.  AYF has an effect only when
192              AST is set to 1. AYF is allowed to vary between 0.0 and 1.0 and
193              its default value is 0.25.
194
195       AYR - Arrow Y-Coord Reference Fraction - Real
196              AYR specifies the perpendicular distance from one side of a
197              filled vector arrowdrawn at the reference length to one of the
198              back tips of the arrowhead. The value represents a fraction of
199              the value of of the reference length and, when added to half the
200              arrow width, determines the Y component of the arrowhead size.
201              See VRL for an explanation of how the reference length is
202              determined.  AYR has an effect only when AST is set to 1.  AYR
203              is allowed to vary between 0.0 and 1.0 and its default value is
204              0.12.
205
206       CLR - Array of GKS Color Indices - Integer Array
207              This parameter represents an array containing the GKS color
208              index to use for coloring the vector when the scalar quantity is
209              less than or equal to the threshold value with the same index in
210              the TVL threshold value array. Depending on the settings of AST
211              and ACM it may specify a set of fill color indexes, a set of
212              line color indexes, or both. In order to access a particular
213              element of the CLR array, you must first set the value of PAI,
214              the parameter array index parameter, to the value of the array
215              element´s index. All elements of the array are set to one
216              initially. Note that the Vectors utility makes no calls to set
217              the GKS color representation (GSCR), nor ever modifies the
218              contents of the CLR array; therefore you are responsible for
219              creating a suitably graduated color palette and assigning the
220              color index values into the CLR array, prior to calling VVECTR.
221              Typically, assuming the desired RGB values have been previously
222              stored in a 2 dimensional 3 x n array called RGB, you loop
223              through the calls that set up the color representation and color
224              index as in the following example for a fourteen color palette:
225
226                   DO 100 I=1,14,1
227                       CALL GSCR (1,I,RGB(1,I),RGB(2,I),RGB(3,I))
228                       CALL VVSETI(´PAI -- Parameter Array Index´, I)
229                       CALL VVSETI(´CLR -- GKS Color Index´, I)
230               100 CONTINUE
231
232              See the descriptions of CTV, NLV, and TVL for details on
233              configuring the vector coloring scheme.
234
235       CPM - Compatibility Mode - Integer
236              Controls the degree of compatibility between pre-Version 3.2
237              capabilities of the Vectors utility and later versions. You can
238              independently control three behaviors using the nine settings
239              provided:
240
241              ·      use of VELVCT and VELVEC input parameters
242
243              ·      use of variables initialized in the VELDAT block data
244                     statement
245
246              ·      use of the old mapping routines, FX, FY, MXF, and MYF.
247
248              Note, however, that when using the Version 3.2 entry points
249              VVINIT and VVECTR, only the third behavior option has any
250              meaning.
251
252              When CPM is set to 0, its default value, the Vectors utility´s
253              behavior varies depending on whether you access it through one
254              of the pre-Version 3.2 entry points (VELVCT, VELVEC, and EZVEC),
255              or through the VVINIT/VVECTR interface. Otherwise, positive
256              values result in invocation of the pre-Version 3.2 mapping
257              routines (FX, FY, MXF, and MYF) for the conversion from data to
258              user coordinates. Negative values cause VVMPXY or perhaps VVUMXY
259              to be used instead. When using the pre-Version 3.2 interface,
260              odd values of CPM cause the data values in the VELDAT block data
261              subroutine to override corresponding values initialized in the
262              Version 3.2 VVDATA block data subroutine, or set by the user
263              calling VVSETx routines. Values of CPM with absolute value
264              greater than two cause some of the input arguments to VELVEC and
265              VELVCT to be ignored. These include FLO, HI, NSET, ISPV, SPV and
266              (for VELVCT only) LENGTH.
267
268              Here is a table of the nine settings of CPM and their effect on
269              the operation of the Vectors utility:
270
271
272              Value   Use FX, FY, etc.          Use VELDAT data   Use input args
273              -----   ----------------          ---------------   --------------
274              -4      no                        no                no
275              -3      no                        yes               no
276              -2      no                        no                yes
277              -1      no                        yes               yes
278              0       old - yes; new - no (*)   yes               yes
279              1       yes                       yes               yes
280              2       yes                       no                yes
281              3       yes                       yes               no
282              4       yes                       no                no
283
284              (*) Old means EZVEC, VELVEC, VELVCT entry point; new,
285              VVINIT/VVECTR.  Only the first column applies to the
286              VVINIT/VVECTR interface. See the velvct man page for more
287              detailed emulation information.
288
289       CTV - Color Threshold Value Control - Integer
290              In conjunction with NLV, this parameter controls vector coloring
291              and the setting of threshold values. The vectors may be colored
292              based on on the vector magnitude or on the contents of a scalar
293              array (VVINIT/VVECTR input argument, P). A table of supported
294              options follows:
295
296              Value          Action
297
298              -2             Color vector arrows based on scalar array data
299                             values; the user is responsible for setting up
300                             threshold level array, TVL
301
302              -1             Color vector arrows based on vector magnitude;
303                             the user is responsible for setting up values of
304                             threshold level array.
305
306              0(default)     Color all vectors according to the current GKS
307                             polyline color index value. Threshold level
308                             array, TVL and GKS color index array, CLR are not
309                             used.
310
311              1              Color vector arrows based on vector magnitude;
312                             VVINIT assigns values to the first NLV elements
313                             of the threshold level array, TVL.
314
315              2              Color vector arrows based on scalar array data
316                             values; VVINIT assigns values to the first NLV
317                             elements of the threshold level array, TVL.
318
319              If you make CTV positive, you must initialize Vectors with a
320              call to VVINIT after the modification.
321
322       DMN - NDC Minimum Vector Size - Real, Read-Only
323              This parameter is read-only and has a useful value only
324              following a call to VVECTR (directly or through the
325              compatibility version of VELVCT). You may retrieve it in order
326              to determine the length in NDC space of the smallest vector
327              actually drawn (in other words, the smallest vector within the
328              boundary of the user coordinate space that is greater than or
329              equal in magnitude to the value of the VLC parameter). It is
330              initially set to a value of 0.0.
331
332       DMX - NDC Maximum Vector Size - Real, Read-Only
333              Unlike DMN this read-only parameter has a potentially useful
334              value betweens calls to VVINIT and VVECTR. However, the value it
335              reports may be different before and after the call to VVECTR.
336              Before the VVECTR call it contains the length in NDC space that
337              would be used to render the maximum size vector assuming the
338              user-settable parameter, VRL is set to its default value of 0.0.
339              After the VVECTR call it contains the NDC length used to render
340              the largest vector actually drawn (in other words, the largest
341              vector within the boundary of the user coordinate space that is
342              less than or equal in magnitude to the value of the VHC
343              parameter). See the section on the VRL parameter for information
344              on using the value of DMX after the VVINIT call in order to
345              adjust proportionally the lengths of all the vectors in the
346              plot.  It is initially set to a value of 0.0.
347
348       DPF - Vector Label Decimal Point Control Flag - Integer
349              If DPF is set to a non-zero value, and the optional vector
350              magnitude labels are enabled, the magnitude values are scaled to
351              fit in the range 1 to 999. The labels will contain 1 to 3 digits
352              and no decimal point. Otherwise, the labels will consist of a
353              number up to six characters long, including a decimal point. By
354              default DPF is set to the value 1.
355
356       LBC - Vector Label Color - Integer
357              This parameter specifies the color to use for the optional
358              vector magnitude labels, as follows:
359
360              Value          Action
361
362              < -1           Draw labels using the current GKS text color
363                             index
364
365              -1 (default)   Draw labels using the same color as the
366                             corresponding vector arrow
367
368              >=0            Draw labels using the LBC value as the GKS text
369                             color index
370
371       LBL - Vector Label Flag - Integer
372              If set non-zero, Vectors draws labels representing the vector
373              magnitude next to each arrow in the field plot.  The vector
374              labels are primarily intended as a debugging aid, since in order
375              to avoid excessive overlap, you must typically set the label
376              text size too small to be readable without magnification. For
377              this reason, as well as for efficiency, unlike the other
378              graphical text elements supported by the Vectors utility, the
379              vector labels are rendered using low quality text.
380
381       LBS - Vector Label Character Size - Real
382              This parameter specifies the size of the characters used for the
383              vector magnitude labels as a fraction of the viewport width. The
384              default value is 0.007.
385
386       LWD - Vector Linewidth - Real
387
388              LWD controls the linewidth used to draw the lines that form
389              vector arrows and wind barbs. When the arrows are filled (AST is
390              set to 1) LWD controls the width of the arrow's outline. If the
391              fill is drawn over the outline (AFO set to 1) then LWD must be
392              set to a value greater than 1.0 in order for the outline to
393              appear properly. When AST has the value 2, LWD controls the
394              width of the line elements of wind barbs. When AST is set to 0,
395              specifying line-drawn vector arrows, the linewidth applies
396              equally to the body of the vector and the arrowhead. Overly
397              thick lines may cause the arrow heads to appear smudged. This
398              was part of the motivation for developing the option of filled
399              vector arrows. Note that since linewidth in NCAR Graphics is
400              always calculated relative to a unit linewidth that is dependent
401              on the output device, you may need to adjust the linewidth value
402              depending on the intended output device to obtain a pleasing
403              plot. The default is 1.0, specifying a device-dependent minimum
404              linewidth.
405
406
407       MAP - Map Transformation Code - Integer
408              MAP defines the transformation between the data and user
409              coordinate space.  Three MAP parameter codes are reserved for
410              pre-defined transformations, as follows:
411
412              Value          Mapping transformation
413
414              0 (default)    Identity transformation between data and user
415                             coordinates: array indices of U, V, and P are
416                             linearly related to data coordinates.
417
418              1              Ezmap transformation: first dimension indices of
419                             U, V, and P are linearly related to longitude;
420                             second dimension indices are linearly related to
421                             latitude.
422
423              2              Polar to rectangular transformation: first
424                             dimension indices of U, V, and P are linearly
425                             related to the radius; second dimension indices
426                             are linearly related to the angle in degrees.
427
428              If MAP has any other value, Vectors invokes the user-modifiable
429              subroutine, VVUMXY, to perform the mapping.  The default version
430              of VVUMXY simply performs an identity transformation. Note that,
431              while the Vectors utility does not actually prohibit the
432              practice, the user is advised not to use negative integers for
433              user-defined mappings, since other utilities in the NCAR
434              Graphics toolkit attach a special meaning to negative mapping
435              codes.
436
437              For all the predefined mappings, the linear relationship between
438              the grid array indices and the data coordinate system is
439              established using the four parameters, XC1, XCM, YC1, and YCN.
440              The X parameters define a mapping for the first and last indices
441              of the first dimension of the data arrays, and the Y parameters
442              do the same for the second dimension. If MAP is set to a value
443              of one, be careful to ensure that the SET parameter is given a
444              value of zero, since the Ezmap routines require a specific user
445              coordinate space for each projection type, and internally call
446              the SET routine to define the user to NDC mapping.  Otherwise,
447              you may choose whether or not to issue a SET call prior to
448              calling VVINIT, modifying the value of SET as required.  See the
449              description of the parameter, TRT, and the vvumxy man page for
450              more information.
451
452       MNC - Minimum Vector Text Block Color - Integer
453              MNC specifies the color of the minimum vector graphical text
454              output block as follows:
455
456              Value          Action
457
458              <-2            Both the vector arrow and the text are colored
459                             using the current text color index.
460
461              -2             If the vectors are colored by magnitude, both the
462                             vector arrow and the text use the GKS color index
463                             associated with the minimum vector magnitude.
464                             Otherwise, the vector arrow uses the current
465                             polyline color index and the text uses the
466                             current text color index.
467
468              -1 (default)   If the vectors are colored by magnitude, the
469                             vector arrow uses the GKS color index associated
470                             with the minimum vector magnitude. Otherwise the
471                             vector arrow uses the current polyline color
472                             index. The text is colored using the current text
473                             color index in either case.
474
475              >= 0           The value of MNC is used as the color index for
476                             both the text and the vector arrow
477
478              See the description of MNT for more information about the
479              minimum vector text block.
480
481       MNP - Minimum Vector Text Block Positioning Mode - Integer
482              This parameter allows you to justify the minimum vector text
483              block, taken as a single unit, relative to the text block
484              position established by the parameters, MNX and MNY. Nine
485              positioning modes are available, as follows:
486
487              Mode           Justification
488
489              -4             The lower left corner of the text block is
490                             positioned at MNX, MNY.
491
492              -3             The center of the bottom edge is positioned at
493                             MNX, MNY.
494
495              -2             The lower right corner is positioned at MNX, MNY.
496
497              -1             The center of the left edge is positioned at MNX,
498                             MNY.
499
500              0              The text block is centered along both axes at
501                             MNX, MNY.
502
503              1              The center of the right edge is positioned at
504                             MNX, MNY.
505
506              2              The top left corner is positioned at MNX, MNY.
507
508              3              The center of the top edge is positioned at MNX,
509                             MNY.
510
511              4 (default)    The top right corner is positioned at MNX, MNY.
512
513              See the description of MNT for more information about the
514              minimum vector text block.
515
516       MNS - Minimum Vector Text Block Character Size - Real
517              MNS specifies the size of the characters used in the minimum
518              vector graphics text block as a fraction of the viewport width.
519              See the description of MNT for more information about the
520              minimum vector text block. The default value of MNS is 0.0075.
521
522       MNT - Minimum Vector Text String - Character* 36
523              The minimum vector graphics text block consists of a user-
524              definable text string centered underneath a horizontal arrow. If
525              the parameter VLC is set negative the arrow is rendered at the
526              size of the reference minimum magnitude vector (which may be
527              smaller than any vector that actually appears in the plot).
528              Otherwise, the arrow is the size of the smallest vector in the
529              plot. Directly above the arrow is a numeric string in
530              exponential format that represents the vector's magnitude.
531
532              Use MNT to modify the text appearing below the vector in the
533              minimum vector graphics text block. Currently the string length
534              is limited to 36 characters. Set MNT to a single space (´ ´) to
535              remove the text block, including the vector arrow and the
536              numeric magnitude string, from the plot. The default value is
537              ´Minimum Vector´
538
539       MNX - Minimum Vector Text Block X Coordinate - Real
540              MNX establishes the X coordinate of the minimum vector graphics
541              text block as a fraction of the viewport width.  Values less
542              than 0.0 or greater than 1.0 are permissible and respectively
543              represent regions to the left or right of the viewport. The
544              actual position of the block relative to MNX depends on the
545              value assigned to MNP. See the descriptions of MNT and MNP for
546              more information about the minimum vector text block. The
547              default value of MNX is 0.475.
548
549       MNY - Minimum Vector Text Block Y Coordinate - Real
550              MNY establishes the Y coordinate of the minimum vector graphics
551              text block as a fraction of the viewport height.  Values less
552              than 0.0 or greater than 1.0 are permissible and respectively
553              represent regions below or above the viewport. The actual
554              position of the block relative to MNY depends on the value
555              assigned to MNP. See the descriptions of MNT and MNP for more
556              information about the minimum vector text block. The default
557              value of MNY is -0.01.
558
559       MSK - Mask To Area Map Flag - Integer
560              Use this parameter to control masking of vectors to an existing
561              area map created by routines in the Areas utility.  When MSK is
562              greater than 0, masking is enabled and an the area map must be
563              set up prior to the call to VVECTR. The area map array and, in
564              addition, the name of a user-definable masked drawing routine,
565              must be passed as input parameters to VVECTR. Various values of
566              the MSK parameter have the following effects:
567
568              Value          Effect
569
570              <= 0 (default) No masking of vectors.
571
572              1              The subroutine ARDRLN is called internally to
573                             decompose the vectors into segments contained
574                             entirely within a single area.  ARDRLN calls the
575                             user-definable masked drawing subroutine.
576
577              >1             Low precision masking. ARGTAI is called
578                             internally to get the area identifiers for the
579                             vector base position point. Then the user-
580                             definable masked drawing subroutine is called to
581                             draw the vector. Vectors with nearby base points
582                             may encroach into the intended mask area.
583
584              See the man page vvudmv for further explanation of masked
585              drawing of vectors
586
587       MXC - Maximum Vector Text Block Color - Integer
588              MXC specifies the color of the maximum vector graphical text
589              output block as follows:
590
591              Value          Action
592
593              <-2            Both the vector arrow and the text are colored
594                             using the current text color index.
595
596              -2             If the vectors are colored by magnitude, both the
597                             vector arrow and the text use the GKS color index
598                             associated with the minimum vector magnitude.
599                             Otherwise, the vector arrow uses the current
600                             polyline color index and the text uses the
601                             current text color index.
602
603              -1 (default)   If the vectors are colored by magnitude, the
604                             vector arrow uses the GKS color index associated
605                             with the minimum vector magnitude. Otherwise the
606                             vector arrow uses the current polyline color
607                             index. The text is colored using the current text
608                             color index in either case.
609
610              >= 0           The value of MXC is used as the color index for
611                             both the text and the vector arrow
612
613              See the description of MXT for more information about the
614              maximum vector text block.
615
616       MXP - Maximum Vector Text Block Positioning Mode - Integer
617              This parameter allows you to justify the maximum vector text
618              block, taken as a single unit, relative to the text block
619              position established by the parameters, MXX and MXY. Nine
620              positioning modes are available, as follows:
621
622              Mode           Justification
623
624              -4             The lower left corner of the text block is
625                             positioned at MXX, MXY.
626
627              -3             The center of the bottom edge is positioned at
628                             MXX, MXY.
629
630              -2             The lower right corner is positioned at MXX, MXY.
631
632              -1             The center of the left edge is positioned at MXX,
633                             MXY.
634
635              0              The text block is centered along both axes at
636                             MXX, MXY.
637
638              1              The center of the right edge is positioned at
639                             MXX, MXY.
640
641              2              The top left corner is positioned at MXX, MXY.
642
643              3              The center of the top edge is positioned at MXX,
644                             MXY.
645
646              4              The top right corner is positioned at MXX, MXY.
647
648              See the description of MXT for more information about the
649              maximum vector text block.
650
651       MXS - Maximum Vector Text Block Character Size - Real
652              MXS specifies the size of the characters used in the maximum
653              vector graphics text block as a fraction of the viewport width.
654              See the description of MXT for more information about the
655              maximum vector text block. The default value is 0.0075.
656
657       MXT - Maximum Vector Text String - Character* 36
658              The maximum vector graphics text block consists of a user-
659              definable text string centered underneath a horizontal arrow. If
660              the parameter VHC is set negative the arrow is rendered at the
661              size of the reference maximum magnitude vector (which may be
662              larger than any vector that actually appears in the plot).
663              Otherwise, the arrow is the size of the largest vector in the
664              plot. Directly above the arrow is a numeric string in
665              exponential format that represents the magnitude of this vector.
666
667              Use MXT to modify the text appearing below the vector in the
668              maximum vector graphics text block. Currently the string length
669              is limited to 36 characters. Set MXT to a single space (´ ´) to
670              completely remove the text block, including the vector arrow and
671              the numeric magnitude string, from the plot. Note that the name
672              "Maximum Vector Text Block" is no longer accurate, since using
673              the parameter VRM it is now possible to establish a reference
674              magnitude that is smaller than the maximum magnitude in the data
675              set. A more accurate name would be "Reference Vector Text
676              Block".  The default value of MXT is ´Maximum Vector´.
677
678       MXX - Maximum Vector Text Block X Coordinate - Real
679              MXX establishes the X coordinate of the maximum vector graphics
680              text block as a fraction of the viewport width.  Values less
681              than 0.0 or greater than 1.0 are permissible and respectively
682              represent regions below or above of the viewport. The actual
683              position of the block relative to MXX depends on the value
684              assigned to MXP. See the descriptions of MXT and MXP for more
685              information about the maximum vector text block. The default
686              value is 0.525.
687
688       MXY - Maximum Vector Text Block Y Coordinate - Real
689              MXY establishes the Y coordinate of the maximum vector graphics
690              text block as a fraction of the viewport width.  Values less
691              than 0.0 or greater than 1.0 are permissible and respectively
692              represent regions below or above the viewport. The actual
693              position of the block relative to MXY depends on the value
694              assigned to MXP. See the descriptions of MXT and MXP for more
695              information about the maximum vector text block.  The default
696              value is -0.01.
697
698       NLV - Number of Colors Levels - Integer
699              NLV specifies the number of color levels to use when coloring
700              the vectors according to data in a scalar array or by vector
701              magnitude.  Anytime CTV has a non-zero value, you must set up
702              the first NLV elements of the color index array CLR. Give each
703              element the value of a GKS color index that must be defined by a
704              call to the the GKS subroutine, GSCR, prior to calling VVECTR.
705              If CTV is less than 0, in addition to setting up the CLR array,
706              you are also responsible for setting the first NLV elements of
707              the threshold values array, TVL to appropriate values. NLV is
708              constrained to a maximum value of 255. The default value of NLV
709              is 0, specifying that vectors are colored according to the value
710              of the GKS polyline color index currently in effect, regardless
711              of the value of CTV.  If CTV is greater than 0, you must
712              initialize Vectors with a call to VVINIT after modifying this
713              parameter.
714
715       PAI - Parameter Array Index - Integer
716              The value of PAI must be set before calling VVGETC, VVGETI,
717              VVGETR, VVSETC, VVSETI, or VVSETR to access any parameter which
718              is an array; it acts as a subscript to identify the intended
719              array element. For example, to set the 10th color threshold
720              array element to 7, use code like this:
721
722               CALL VVSETI (´PAI - PARAMETER ARRAY INDEX´,10)
723               CALL VVSETI (´CLR - Color Index´,7)
724
725              The default value of PAI is one.
726
727       PLR - Polar Input Mode - Integer
728              When PLR is greater than zero, the vector component arrays are
729              considered to contain the field data in polar coordinate form:
730              the U array is treated as containing the vector magnitude and
731              the V array as containing the vector angle. Be careful not to
732              confuse the PLR parameter with the MAP parameter set to polar
733              coordinate mode (2). The MAP parameter relates to the location
734              of the vector, not its value. Here is a table of values for PLR:
735
736              Value          Meaning
737
738              0 (default)    U and V arrays contain data in cartesian
739                             component form.
740
741              1              U array contains vector magnitudes; V array
742                             contains vector angles in degrees.
743
744              2              U array contain vector magnitudes; V array
745                             contains vector angles in radians.
746
747              You must initialize Vectors with a call to VVINIT after
748              modifying this parameter.
749
750       PMN - Minimum Scalar Array Value - Real, Read-Only
751              You may retrieve the value specified by PMN at any time after a
752              call to VVINIT. It will contain a copy of the minimum value
753              encountered in the scalar data array. If no scalar data array
754              has been passed into VVINIT it will have a value of 0.0.
755
756       PMX - Maximum Scalar Array Value - Real
757              You may retrieve the value specified by PMX at any time after a
758              call to VVINIT. It contains a copy of the maximum value
759              encountered in the scalar data array.  If no scalar data array
760              has been passed into VVINIT it will have a value of 0.0.
761
762       PSV - P Array Special Value - Real
763              Use PSV to indicate the special value that flags an unknown data
764              value in the P scalar data array. This value will not be
765              considered in the determination of the data set maximum and
766              minimum values. Also, depending on the setting of the SPC
767              parameter, the vector may be specially colored to flag the
768              unknown data point, or even eliminated from the plot. You must
769              initialize Vectors with a call to VVINIT after modifying this
770              parameter.
771
772       SET - SET Call Flag - Integer
773              Give SET the value 0 to inhibit the SET call VVINIT performs by
774              default. Arguments 5-8 of a SET call made by the user must be
775              consistent with the ranges of the user coordinates expected by
776              Vectors. This is determined by the mapping from grid to data
777              coordinates as specified by the values of the parameters XC1,
778              XCM, YC1, YCN, and also by the mapping from data to user
779              coordinates established by the MAP parameter. You must
780              initialize Vectors with a call to VVINIT after modifying this
781              parameter. The default value of SET is 1.
782
783       SPC - Special Color - Integer
784              SPC controls special value processing for the optional scalar
785              data array used to color the vectors, as follows:
786
787              Value          Effect
788
789              < 0 (default)  The P scalar data array is not examined for
790                             special values.
791
792              0              Vectors at P scalar array special value locations
793                             are not drawn.
794
795              > 0            Vectors at P scalar array special value locations
796                             are drawn using color index SPC.
797
798              You must initialize Vectors with a call to VVINIT after
799              modifying this parameter.
800
801       SVF - Special Value Flag - Integer
802              The special value flag controls special value processing for the
803              U and V vector component data arrays. Special values may appear
804              in either the U or V array or in both of them. Five different
805              options are available (although the usefulness of some of the
806              choices is debatable):
807
808              Value          Effect
809
810              0 (default)    Neither the U nor the V array is examined for
811                             special values
812
813              1              Vectors with special values in the U array are
814                             not drawn
815
816              2              Vectors with special values in the V array are
817                             not drawn
818
819              3              Vectors with special values in either the U or V
820                             array are not drawn
821
822              4              Vectors with special values in both the U and V
823                             arrays are not drawn
824
825              The U and V special values are defined by setting parameters USV
826              and VSV. You must initialize Vectors with a call to VVINIT after
827              modifying this parameter.
828
829       TRT - Transformation Type - Integer
830              As currently implemented, TRT further qualifies the mapping
831              transformation specified by the MAP parameter, as follows:
832
833              Value          Effect
834
835              -1             Direction, magnitude, and location are all
836                             transformed. This option is not currently
837                             supported by any of the pre-defined coordinate
838                             system mappings.
839
840              0              Only location is transformed
841
842              1 (default)    Direction and location are transformed
843
844              This parameter allows you to distinguish between a system that
845              provides a mapping of location only into an essentially
846              cartesian space, and one in which the space itself mapped. To
847              understand the difference, using polar coordinates as an
848              example, imagine a set of wind speed monitoring units located on
849              a radial grid around some central point such as an airport
850              control tower. Each unit´s position is defined in terms of its
851              distance from the tower and its angular direction from due east.
852              However, the data collected by each monitoring unit is
853              represented as conventional eastward and northward wind
854              components.  Assuming the towers´s location is at a moderate
855              latitude, and the monitoring units are reasonably ´local´, this
856              is an example of mapping a radially defined location into a
857              nearly cartesian space (i.e. the eastward components taken alone
858              all point in a single direction on the plot, outlining a series
859              of parallel straight lines). One would set MAP to two (for the
860              polar transformation) and TRT to zero to model this data on a
861              plot generated by the Vectors utility.
862
863              On the other hand, picture a set of wind data, again given as
864              eastward and northward wind components, but this time the center
865              of the polar map is actually the south pole. In this case, the
866              eastward components do not point in a single direction; instead
867              they outline a series of circles around the pole. This is a
868              space mapping transformation: one would again set MAP to two,
869              but TRT would be set to one to transform both direction and
870              location.
871
872              Changing the setting of this parameter affects the end results
873              only when a non-uniform non-linear mapping occurs at some point
874              in the transformation pipeline. For this discussion a uniform
875              linear transformation is defined as one which satisfies the
876              following equations:
877
878               x_out = x_offset + scale_constant * x_in
879               y_out = y_offset + scale_constant * y_in
880
881              If scale_constant is not the same for both the X axis and the Y
882              axis then the mapping is non-uniform.
883
884              This option is currently implemented only for the pre-defined
885              MAP parameter codes, 0 and 2, the identity mapping and the polar
886              coordinate mapping. However, it operates on a different stage of
887              the transformation pipeline in each case. The polar mapping is
888              non-linear from data to user coordinates. The identity mapping,
889              even though necessarily linear over the data to user space
890              mapping, can have a non-uniform mapping from user to NDC space,
891              depending on the values given to the input parameters of the SET
892              call. This will be the case whenever the LL input parameter is
893              other than one, or when LL equals one, but the viewport and the
894              user coordinate boundaries do not have the same aspect ratio.
895              Thus for a MAP value of 2, TRT affects the mapping between data
896              and user space, whereas for MAP set to 0, TRT influences the
897              mapping between user and NDC space.
898
899       TVL - Array of Threshold Values - Real Array
900              TVL is an array of threshold values that is used to determine
901              the individual vector color, when CTV and NLV are both non-zero.
902              For each vector the TVL array is searched for the smallest value
903              greater than or equal to the scalar value associated with the
904              vector. The array subscript of this element is used as an index
905              into the CLR array.  Vectors uses the GKS color index found at
906              this element of the CLR array to set the color for the vector.
907              Note that Vectors assumes that the threshold values are
908              monotonically increasing.
909
910              When CTV is less than 0, you are responsible for assigning
911              values to the elements of TVL yourself. To do this, first set
912              the PAI parameter to the index of the threshold level element
913              you want to define, then call VVSETR to set TVL to the
914              appropriate threshold value for this element. Assuming the
915              desired values have previously been stored in a array named
916              TVALS, you could assign the threshold values for a fourteen
917              level color palette using the following loop:
918
919                   DO 100 I=1,14,1
920                       CALL VVSETI(PAI -- Parameter Array Index, I)
921                       CALL VVSETR(TVL -- Threshold Value, TVALS(I))
922               100 CONTINUE
923
924              When CTV is greater than 0, Vectors assigns values into TVL
925              itself. Each succeeding element value is greater than the
926              preceding value by the value of the expression:
927
928               (maximum_data_value - minimum_data_value) / NLV
929
930              where the data values are either from the scalar data array or
931              are the magnitudes of the vectors in the vector component
932              arrays. The first value is equal to the minimum value plus the
933              expression; the final value (indexed by the value of NLV) is
934              equal to the maximum value. If Vectors encounters a value
935              greater than the maximum value in the TVL array while processing
936              the field data, it gives the affected vector the color
937              associated with the maximum TVL value.
938
939       USV - U Array Special Value - Real
940              USV is the U vector component array special value. It is a value
941              outside the range of the normal data used to indicate that there
942              is no valid data for this grid location. When SVF is set to 1 or
943              3, Vectors will not draw a vector whose U component has the
944              special value. You must initialize Vectors with a call to VVINIT
945              after modifying this parameter. It has a default value of 1.0
946              E12.
947
948       VFR - Minimum Vector Fractional Length - Real
949              Use this parameter to adjust the realized size of the reference
950              minimum magnitude vector relative to the reference maximum
951              magnitude vector in order to improve the appearance or perhaps
952              the information content of the plot. Specify VFR as a value
953              between 0.0 and 1.0, where 0.0 represents an unmodified linear
954              scaling of the realized vector length, in proportion to
955              magnitude, and 1.0 specifies that the smallest vector be
956              represented at 1.0 times the length of the largest vector,
957              resulting in all vectors, regardless of magnitude, having the
958              same length on the plot. A value of 0.5 means that the smallest
959              magnitude vector appears half as long as the largest magnitude
960              vector; intermediate sizes are proportionally scaled to lengths
961              between these extremes. Where there is a wide variation in
962              magnitude within the vector field, you can use this parameter to
963              increase the size of the smallest vectors to a usefully visible
964              level. Where the variation is small, you can use the parameter
965              to exaggerate the differences that do exist. See also the
966              descriptions of VRL, VLC, VHC, and VRM. The default value is
967              0.0.
968
969       VHC - Vector High Cutoff Value - Real
970              If the parameter VRM is set to a value greater than 0.0, it
971              supercedes the use of VHC to specify the reference magnitude.
972              VRM allows greater flexibility in that it can be used to specify
973              an arbitrary reference magnitude that need not be the maximum
974              magnitude contained in the data set. VHC can still be used to
975              set a high cutoff value -- no vectors with magnitude greater
976              than the cutoff value will be displayed in the plot.
977
978              If VRM has its default value, 0.0, VHC specifies the reference
979              maximum magnitude represented by an arrow of length VRL (as a
980              fraction of the viewport width). The realized length of each
981              individual vector in the plot is based on its magnitude relative
982              to the reference maximum magnitude and, if VFR is non-zero, the
983              reference minimum magnitude (as specified by VLC). Note that the
984              reference maximum magnitude may be greater than the magnitude of
985              any vector in the dataset. The effect of this parameter varies
986              depending on its value, as follows:
987
988              Value          Effect
989
990              < 0.0          The absolute value of VHC unconditionally
991                             determines the reference maximum magnitude.
992                             Vectors in the dataset with magnitude greater
993                             than VHC are not displayed.
994
995              0.0 (default)  The vector with the greatest magnitude in the
996                             dataset determines the reference maximum
997                             magnitude.
998
999              > 0.0          The minimum of VHC and the vector with the
1000                             greatest magnitude in the data set determines the
1001                             reference maximum magnitude. Vectors in the
1002                             dataset with magnitude greater than VHC are not
1003                             displayed.
1004
1005              Typically, for direct comparison of the output of a series of
1006              plots, you would set VHC to a negative number, the absolute
1007              value of which is greater than any expected vector magnitude in
1008              the series. You can turn on Vectors statistics reporting using
1009              the parameter VST in order to see if any vectors in the datasets
1010              do exceed the maximum magnitude you have specified. See also the
1011              descriptions of the parameters VRM, VRL, DMX, VLC, and VFR.
1012
1013       VLC - Vector Low Cutoff Value - Real
1014              Use this parameter to prevent vectors smaller than the specified
1015              magnitude from appearing in the output plot. VLC also specifies
1016              the reference minimum magnitude that is rendered at the size
1017              specified by the product of VRL and VFR (as a fraction of the
1018              viewport width), when VFR is greater than 0.0. Note that the
1019              reference minimum magnitude may be smaller than the magnitude of
1020              any vector in the dataset. The effect of this parameter varies
1021              depending on its value, as follows:
1022
1023              Value          Effect
1024
1025              < 0.0          The absolute value of VLC unconditionally
1026                             determines the reference minimum magnitude.
1027                             Vectors in the dataset with magnitude less than
1028                             VLC do not appear.
1029
1030              0.0 (default)  The vector with the minimum magnitude in the
1031                             dataset determines the reference minimum
1032                             magnitude.
1033
1034              > 0.0          The maximum of VLC and the vector with the least
1035                             magnitude in the data set determines the
1036                             reference minimum magnitude. Vectors in the
1037                             dataset with magnitude less than VLC do not
1038                             appear.
1039
1040              The initialization subroutine, VVINIT, calculates the magnitude
1041              of all the vectors in the vector field, and stores the maximum
1042              and minimum values. You may access these values by retrieving
1043              the read-only parameters, VMX and VMN.  Thus it is possible to
1044              remove the small vectors without prior knowledge of the data
1045              domain. The following code fragment illustrates how the smallest
1046              10% of the vectors could be removed:
1047
1048               CALL VVINIT(...
1049               CALL VVGETR(´VMX - Vector Maximum Magnitude´, VMX)
1050               CALL VVGETR(´VMN - Vector Minimum Magnitude´, VMN)
1051               CALL VVSETR(´VLC - Vector Low Cutoff Value´,
1052              +     VMN+0.1*(VMX-VMN))
1053               CALL VVECTR(...
1054
1055
1056              On the other hand, when creating a series of plots that you
1057              would like to compare directly and you are using VFR to set a
1058              minimum realized size for the vectors, you can ensure that all
1059              vectors of a particular length represent the same magnitude on
1060              all the plots by setting both VHC and VLC to negative values. If
1061              you do not actually want to remove any vectors from the plot,
1062              make VLC smaller in absolute value than any expected magnitude.
1063              You can turn on Vectors statistics reporting using the parameter
1064              VST in order to see if any vectors in the datasets are less the
1065              minimum magnitude you have specified. See also the descriptions
1066              of parameters VFR, VRL, VHC, DMN, and VRM.
1067
1068       VMD - Vector Minimum Distance - Real
1069              If VMD is set to a value greater than 0.0, it specifies, as a
1070              fraction of the viewport width, a minimum distance between
1071              adjacent vectors arrows in the plot. The distribution of vectors
1072              is analyzed and then vectors are selectively removed in order to
1073              ensure that the remaining vectors are separated by at least the
1074              specified distance. The thinning algorithm requires that you
1075              supply Vectors with a work array twice the size of the VVINIT
1076              arguments N and M multiplied together. Use of this capability
1077              adds some processing time to the execution of Vectors. If VMD is
1078              set to a value greater than 0.0 and no work array is provided,
1079              an error condition results.
1080
1081              If the data grid is transformed in such a way that adjacent grid
1082              cells become very close in NDC space, as for instance in many
1083              map projections near the poles, you can use this parameter to
1084              reduce the otherwise cluttered appearance of these regions of
1085              the plot. The default value of VMD is 0.0.
1086
1087       VMN - Minimum Vector Magnitude - Real, Read-Only
1088              After a call to VVINIT, VMN contains the value of the minimum
1089              vector magnitude in the U and V vector component arrays. Later,
1090              after VVECTR is called, it is modified to contain the magnitude
1091              of the smallest vector actually displayed in the plot. This is
1092              the vector with the smallest magnitude greater than or equal to
1093              the value specified by VLC, the vector low cutoff parameter,
1094              (0.0 if VLC has its default value) that falls within the user
1095              coordinate window boundaries. The value contained in VMN is the
1096              same as that reported as the 'Minimum plotted vector magnitude'
1097              when Vectors statistics reporting is enabled. It may be larger
1098              than the reference minimum magnitude reported by the minimum
1099              vector text block if you specify the VLC parameter as a negative
1100              value. VMN is initially set to a value of 0.0.
1101
1102       VMX - Maximum Vector Magnitude - Real, Read-Only
1103              After a call to VVINIT, VMX contains the value of the maximum
1104              vector magnitude in the U and V vector component arrays. Later,
1105              after VVECTR is called, it is modified to contain the magnitude
1106              of the largest vector actually displayed in the plot. This is
1107              the vector with the largest magnitude less than or equal to the
1108              value specified by VHC, the vector high cutoff parameter, (the
1109              largest floating point value available on the machine if VHC has
1110              its default value, 0.0) that falls within the user coordinate
1111              window boundaries. The value contained in VMX is the same as
1112              that reported as the 'Maximum plotted vector magnitude' when
1113              Vectors statistics reporting is enabled. It may be smaller than
1114              the reference maximum magnitude reported by the maximum vector
1115              text block if you specify the VHC parameter as a negative value.
1116              VMX is initially set to a value of 0.0.
1117
1118       VPB - Viewport Bottom - Real
1119              The parameter VPB has an effect only when SET is non-zero,
1120              specifying that Vectors should do the call to SET. It specifies
1121              a minimum boundary value for the bottom edge of the viewport in
1122              NDC space, and is constrained to a value between 0.0 and 1.0. It
1123              must be less than the value of the Viewport Top parameter, VPT.
1124              The actual value of the viewport bottom edge used in the plot
1125              may be greater than the value of VPB, depending on the setting
1126              of the Viewport Shape parameter, VPS.  You must initialize
1127              Vectors with a call to VVINIT after modifying this parameter.
1128              The default value of VPB is 0.05.
1129
1130       VPL - Viewport Left - Real
1131              The parameter VPL has an effect only when SET is non-zero,
1132              specifying that Vectors should do the call to SET. It specifies
1133              a minimum boundary value for the left edge of the viewport in
1134              NDC space, and is constrained to a value between 0.0 and 1.0. It
1135              must be less than the value of the Viewport Right parameter,
1136              VPR. The actual value of the viewport left edge used in the plot
1137              may be greater than the value of VPL, depending on the setting
1138              of the Viewport Shape parameter, VPS.  You must initialize
1139              Vectors with a call to VVINIT after modifying this parameter.
1140              The default value of VPL is 0.05.
1141
1142       VPO - Vector Positioning Mode - Integer
1143              VPO specifies the position of the vector arrow in relation to
1144              the grid point location of the vector component data.  Three
1145              settings are available, as follows:
1146
1147              Value          Effect
1148
1149              <0             The head of the vector arrow is placed at the
1150                             grid point location
1151
1152              0 (default)    The center of the vector arrow is placed at the
1153                             grid point location
1154
1155              >0             The tail of the vector arrow is placed at the
1156                             grid point location
1157
1158       VPR - Viewport Right - Real
1159              The parameter VPR has an effect only when SET is non-zero,
1160              specifying that Vectors should do the call to SET. It specifies
1161              a maximum boundary value for the right edge of the viewport in
1162              NDC space, and is constrained to a value between 0.0 and 1.0. It
1163              must be greater than the value of the Viewport Left parameter,
1164              VPL. The actual value of the viewport right edge used in the
1165              plot may be less than the value of VPR, depending on the setting
1166              of the Viewport Shape parameter, VPS.  You must initialize
1167              Vectors with a call to VVINIT after modifying this parameter.
1168              The default value of VPR is 0.95.
1169
1170       VPS - Viewport Shape - Real
1171              The parameter VPS has an effect only when SET is non-zero,
1172              specifying that Vectors should do the call to SET; it specifies
1173              the desired viewport shape, as follows:
1174
1175              Value          Effect
1176
1177              <0.0           The absolute value of VPS specifies the shape to
1178                             use for the viewport., as the ratio of the
1179                             viewport width to its height,
1180
1181              0.0            The viewport completely fills the area defined by
1182                             the boundaries specifiers, VPL, VPR, VPB, VPT
1183
1184              >0.0,<1.0 (0.25, default)
1185                             Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape
1186                             if MIN(R, 1.0/R) is greater than VPS. Otherwise
1187                             determine the shape as when VPS is equal to 0.0.
1188
1189              >= 1.0         Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape
1190                             if MAX(R, 1.0/R) is less than VPS. Otherwise make
1191                             the viewport a square.
1192
1193              The viewport, whatever its final shape, is centered in, and made
1194              as large as possible in, the area specified by the parameters
1195              VPB, VPL, VPR, and VPT. You must initialize Vectors with a call
1196              to VVINIT after modifying this parameter. The default value of
1197              VPS is 25.
1198
1199       VPT - Viewport Top - Real
1200              The parameter VPT has an effect only when SET is non-zero,
1201              specifying that Vectors should do the call to SET. It specifies
1202              a maximum boundary value for the top edge of the viewport in NDC
1203              space, and is constrained to a value between 0.0 and 1.0. It
1204              must be greater than the value of the Viewport Bottom parameter,
1205              VPB. The actual value of the viewport top edge used in the plot
1206              may be less than the value of VPT, depending on the setting of
1207              the Viewport Shape parameter, VPS.  You must initialize Vectors
1208              with a call to VVINIT after modifying this parameter. The
1209              default value of VPT is 0.95.
1210
1211       VRL - Vector Reference Length - Real
1212              Use this parameter to specify the realized length of the
1213              reference magnitude vector as a fraction of the viewport width.
1214              Based on this value a reference length in NDC units is
1215              established, from which the length of all vectors in the plot is
1216              derived. The relationship between magnitude and length also
1217              depends on the setting of the minimum vector magnitude fraction
1218              parameter, VFR, but, given the default value of VFR (0.0), the
1219              length of each vector is simply proportional to its relative
1220              magnitude. Note that the arrow size parameters, AMN and AMX,
1221              allow independent control over the minimum and maximum size of
1222              the vector arrowheads.
1223
1224              Given a reference length, Vectors calculates a maximum length
1225              based on the ratio of the reference magnitude to the larger of
1226              the maximum magnitude in the data set and the reference
1227              magnitude itself. This length is accessible in units of NDC via
1228              the read-only parameter, DMX. If VRL is set less than or equal
1229              to 0.0, VVINIT calculates a default value for DMX, based on the
1230              size of a grid box assuming a linear mapping from grid
1231              coordinates to NDC space. The value chosen is one half the
1232              diagonal length of a grid box. By retrieving the value of DMX
1233              and calling GETSET to retrieve the viewport boundaries after the
1234              call to VVINIT, you can make relative adjustments to the vector
1235              length, as shown by the following example, where the maximum
1236              vector length is set to 1.5 times its default value:
1237
1238               CALL VVINIT(...
1239               CALL VVGETR(´DMX - NDC Maximum Vector Size´, DMX)
1240               CALL GETSET(VL,VR,VB,VT,UL,UR,UB,UT,LL)
1241               VRL = 1.5 * DMX / (VR - VL)
1242               CALL VVSETR(´VRL - Vector Realized Length´, VRL)
1243               CALL VVECTR(...
1244
1245              When VVECTR sees that VRL is greater than 0.0, it will calculate
1246              a new value for DMX. If VRL is never set, the initially
1247              calculated value of DMX is used as the reference length. Do not
1248              rely on the internal parameters used for setting the viewport,
1249              VPL, VPR, VPB and VPT to retrieve information about viewport in
1250              lieu of using the GETSET call. These values are ignored entirely
1251              if the SET parameter is zero, and even if used, the viewport may
1252              be adjusted from the specified values depending on the setting
1253              of the viewport shape parameter, VPS. See also the descriptions
1254              of VFR, VRM, and VHC. The default value of VRL is 0.0.
1255
1256       VRM - Vector Reference Magnitude - Real
1257              The introduction of the parameter VRM means that it is now
1258              possible to specify an arbitrary vector magnitude as the
1259              reference magnitude appearing in the "Maximum Vector Text Block"
1260              annotation. The reference magnitude no longer needs to be
1261              greater or equal to the largest magnitude in the data set.  When
1262              VRM has a value greater than 0.0, it specifies the magnitude of
1263              the vector arrow drawn at the reference length. See VRL for an
1264              explanation of how the reference length is determined. If VRM is
1265              less than or equal to 0.0, the reference magnitude is determined
1266              by the value of VHC, the vector high cutoff value. If, in turn,
1267              VHC is equal to 0.0 the maximum magnitude in the vector field
1268              data set becomes the reference magnitude. The default value of
1269              VRM is 0.0.
1270
1271       VST - Vector Statistics Output Flag - Integer
1272              If VST is set to one, VVECTR writes a summary of its operation
1273              to the default logical output unit, including the number of
1274              vectors plotted, number of vectors rejected, minimum and maximum
1275              vector magnitudes, and if coloring the vectors according to data
1276              in the scalar array, the maximum and minimum scalar array values
1277              encountered. Here is a sample of the output:
1278
1279               VVECTR Statistics
1280                                   Vectors plotted:  906
1281               Vectors rejected by mapping routine:  0
1282                   Vectors under minimum magnitude:  121
1283                    Vectors over maximum magnitude:  0
1284                         Other zero length vectors:  0
1285                           Rejected special values:  62
1286                  Minimum plotted vector magnitude:  9.94109E-02
1287                  Maximum plotted vector magnitude:      1.96367
1288                              Minimum scalar value:     -1.00000
1289                              Maximum scalar value:      1.00000
1290
1291       VSV - V Array Special Value - Real
1292              VSV is the V vector component array special value. It is a value
1293              outside the range of the normal data used to indicate that there
1294              is no valid data for this grid location. When SVF is set to 2 or
1295              3, Vectors will not draw a vector whose V component has the
1296              special value. You must initialize Vectors with a call to VVINIT
1297              after modifying this parameter. It has a default value of 1.0
1298              E12.
1299
1300
1301       WBA - Wind Barb Angle - Real
1302
1303              WBA sets the angle of the wind barb ticks in degrees as measured
1304              clockwise from the vector direction. It also sets the angle
1305              between the hypotenuse of the triangle defining the pennant
1306              polygon and the vector direction. You can render southern
1307              hemisphere wind barbs, which by convention, have their ticks and
1308              pennants on the other side of the shaft, by setting WBA to a
1309              negative value. WBA has an effect only when AST has the value 2.
1310
1311
1312       WBC - Wind Barb Calm Circle Size - Real
1313
1314              WBC sets the diameter of the circle used to represent small
1315              vector magnitudes (less than 2.5) as a fraction of the overall
1316              wind barb length (the value of the VRL parameter). WBC has an
1317              effect only when AST has the value 2.
1318
1319
1320       WBD - Wind Barb Distance Between Ticks - Real
1321
1322              WBD sets the distance between adjacent wind barbs ticks along
1323              the wind barb shaft as a fraction of the overall wind barb
1324              length (the value of the VRL parameter). Half this distance is
1325              used as the spacing between adjacent wind barb pennants. Note
1326              that there is nothing to to prevent ticks and/or pennants from
1327              continuing off the end of the shaft if a vector of high enough
1328              magnitude is encountered. You are responsible for adjusting the
1329              parameters appropriately for the range of magnitudes you need to
1330              handle. WBD has an effect only when AST has the value 2.
1331
1332
1333       WBS - Wind Barb Scale Factor - Real
1334
1335              WBS specifies a factor by which magnitudes passed to the wind
1336              barb drawing routines are to be scaled. It can be used to
1337              convert vector data given in other units into the conventional
1338              units used with wind barbs, which is knots. For instance, if the
1339              data are in meters per second, you could set WBS to 1.8974 to
1340              create a plot with conventional knot-based wind barbs. Note that
1341              setting WBS does not currently have any effect on the magnitude
1342              values written into the maximum or minimum vector legends.  WBS
1343              has an effect only when AST has the value 2.
1344
1345
1346       WBT - Wind Barb Tick Size - Real
1347
1348              WBT the length of the wind barb ticks as a fraction of the
1349              overall length of a wind barb (the value of the VRL parameter).
1350              The wind barb length is defined as the length of the wind barb
1351              shaft plus the projection of a full wind barb tick along the
1352              axis of the shaft. Therefore, increasing the value of WBT, for a
1353              given value of VRL has the effect of reducing the length of the
1354              shaft itself somewhat. You may need to increase VRL itself to
1355              compensate. WBT also sets the hypotenuse length of the triangle
1356              defining the pennant polygon. WBT has an effect only when AST
1357              has the value 2.
1358
1359
1360       WDB - Window Bottom - Real
1361              When VVINIT does the call to SET, the parameter WDB is used to
1362              determine argument number 7, the user Y coordinate at the bottom
1363              of the window. If WDB is not equal to WDT, WDB is used. If WDB
1364              is equal to WDT, but YC1 is not equal to YCN, then YC1 is used.
1365              Otherwise, the value 1.0 is used. You must initialize Vectors
1366              with a call to VVINIT after modifying this parameter. The
1367              default value of WDB is 0.0.
1368
1369       WDL - Window Left - Real
1370              When VVINIT the call to SET, the parameter WDL is used to
1371              determine argument number 5, the user X coordinate at the left
1372              edge of the window. If WDL is not equal to WDR, WDL is used. If
1373              WDL is equal to WDR, but XC1 is not equal to XCM, then XC1 is
1374              used. Otherwise, the value 1.0 is used. You must initialize
1375              Vectors with a call to VVINIT after modifying this parameter.
1376              The default value of WDL is 0.0.
1377
1378       WDR - Window Right - Real
1379              When VVINIT does the call to SET, the parameter WDR is used to
1380              determine argument number 6, the user X coordinate at the right
1381              edge of the window. If WDR is not equal to WDL, WDR is used. If
1382              WDR is equal to WDL, but XCM is not equal to XC1, then XCM is
1383              used.  Otherwise, the value of the VVINIT input parameter, M,
1384              converted to a real, is used. You must initialize Vectors with a
1385              call to VVINIT after modifying this parameter. The default value
1386              of WDR is 0.0.
1387
1388       WDT - Window Top - Real
1389              When VVINIT does the call to SET, the parameter WDB is used to
1390              determine argument number 8, the user Y coordinate at the top of
1391              the window. If WDT is not equal to WDB, WDT is used. If WDT is
1392              equal to WDB, but YCN is not equal to YC1 then YCN is used.
1393              Otherwise, the value of the VVINIT input parameter, N, converted
1394              to a real, is used.  You must initialize Vectors with a call to
1395              VVINIT after modifying this parameter. The default value of WDT
1396              is 0.0.
1397
1398       XC1 - X Coordinate at Index 1 - Real
1399              The parameter XC1 specifies the X coordinate value that
1400              corresponds to a value of 1 for the first subscript of the U, V,
1401              vector component arrays as well as for the P scalar data array,
1402              if used. Together with XCM, YC1, and YCN it establishes the
1403              mapping from grid coordinate space to data coordinate space. If
1404              XC1 is equal to XCM, 1.0 will be used. You must initialize
1405              Vectors with a call to VVINIT after modifying this parameter.
1406              The default value of XC1 is 0.0.
1407
1408       XCM - X Coordinate at Index M - Real
1409              The parameter XCM specifies the X coordinate value that
1410              corresponds to the value of the VVINIT input parameter, M, for
1411              the first subscript of the U and V vector component arrays as
1412              well as for the P scalar data array, if used.  Together with
1413              XC1, YC1, and YCN it establishes the mapping from grid
1414              coordinate space to data coordinate space. If XC1 is equal to
1415              XCM, the value of M, converted to a real, will be used. You must
1416              initialize Vectors with a call to VVINIT after modifying this
1417              parameter. The default value of XCM is 0.0.
1418
1419       XIN - X Axis Array Increment (Grid) - Integer
1420              XIN controls the step size through first dimensional subscripts
1421              of the U,V vector component arrays and also through the P scalar
1422              data array if it is used. For dense arrays plotted at a small
1423              scale, you could set this parameter to a value greater than one
1424              to reduce the crowding of the vectors and hopefully improve the
1425              intelligibility of the plot. The grid point with subscripts
1426              (1,1) is always included in the plot, so if XIN has a value of
1427              three, for example, only grid points with first dimension
1428              subscripts 1, 4, 7... (and so on) will be plotted. See also YIN.
1429              You must initialize Vectors with a call to VVINIT after
1430              modifying this parameter. The default value of XIN is 1.
1431
1432       YC1 - Y Coordinate at Index 1 - Real
1433              The parameter YC1 specifies the Y coordinate value that
1434              corresponds to a value of 1 for the first subscript of the U, V,
1435              vector component arrays as well as for the P scalar data array,
1436              if used. Together with YCN, XC1, and XCM it establishes the
1437              mapping from grid coordinate space to data coordinate space. If
1438              YC1 is equal to YCN, 1.0 will be used. You must initialize
1439              Vectors with a call to VVINIT after modifying this parameter.
1440              The default value of YC1 is 0.0.
1441
1442       YCN - Y Coordinate at Index N - Real
1443              The parameter YCN specifies the Y coordinate value that
1444              corresponds to the value of the VVINIT input parameter, N, for
1445              the second subscript of the U and V vector component arrays as
1446              well as the P scalar data array, if used.  Together with YC1,
1447              XC1, and XCM it establishes the mapping from grid coordinate
1448              space to data coordinate space. If YC1 is equal to YCN, the
1449              value of N, converted to a real, will be used. You must
1450              initialize Vectors with a call to VVINIT after modifying this
1451              parameter. The default value of YCN is 0.0.
1452
1453       YIN - Y Axis Array Increment (Grid) - Integer
1454              YIN controls the step size through the second dimension
1455              subscripts of the U and V vector component arrays and also
1456              through the P scalar data array if it is used. For dense arrays
1457              plotted at a small scale, you could set this parameter to a
1458              value greater than one to reduce the crowding of the vectors and
1459              hopefully improve the intelligibility of the plot. The grid
1460              point with subscripts (1,1) is always included in the plot, so
1461              if YIN has a value of three, for example, only grid points with
1462              second dimension subscripts 1, 4, 7... (and so on) will be
1463              plotted. See also XIN. You must initialize Vectors with a call
1464              to VVINIT after modifying this parameter. The default value of
1465              YIN is 1.
1466
1467       ZFC - Zero Field Text Block Color - Integer
1468              If ZFC is greater or equal to zero, it specifies the GKS color
1469              index to use to color the Zero Field text block.  Otherwise the
1470              Zero Field text block is colored using the current GKS text
1471              color index. The default value of ZFC is -1.
1472
1473       ZFP - Zero Field Text Block Positioning Mode - Integer
1474              The ZFP parameter allows you to justify, using any of the 9
1475              standard justification modes, the Zero Field text block unit
1476              with respect to the position established by the parameters, ZFX
1477              and ZFY The position modes are supported as follows:
1478
1479              Mode           Justification
1480
1481              -4             The lower left corner of the text block is
1482                             positioned at ZFX, ZFY.
1483
1484              -3             The center of the bottom edge is positioned at
1485                             ZFX, ZFY.
1486
1487              -2             The lower right corner is positioned at ZFX, ZFY.
1488
1489              -1             The center of the left edge is positioned at ZFX,
1490                             ZFY.
1491
1492              0 (default)    The text block is centered along both axes at
1493                             ZFX, ZFY.
1494
1495              1              The center of the right edge is positioned at
1496                             ZFX, ZFY.
1497
1498              2              The top left corner is positioned at ZFX, ZFY.
1499
1500              3              The center of the top edge is positioned at ZFX,
1501                             ZFY.
1502
1503              4              The top right corner is positioned at ZFX, ZFY.
1504
1505       ZFS - Zero Field Text Block Character Size - Real
1506              ZFS specifies the size of the characters used in the Zero Field
1507              graphics text block as a fraction of the viewport width. The
1508              default value is 0.033.
1509
1510       ZFT - Zero Field Text String - Character* 36
1511              Use ZFT to modify the text of the Zero Field text block.  The
1512              Zero Field text block may appear whenever the U and V vector
1513              component arrays contain data such that all the grid points
1514              otherwise eligible for plotting contain zero magnitude vectors.
1515              Currently the string length is limited to 36 characters. Set ZFT
1516              to a single space (´ ´) to prevent the text from being
1517              displayed. The default value for the text is ´Zero Field´.
1518
1519       ZFX - Zero Field Text Block X Coordinate - Real
1520              ZFX establishes the X coordinate of the Zero Field graphics text
1521              block as a fraction of the viewport width. Values less than 0.0
1522              or greater than 1.0 are permissible and respectively represent
1523              regions to the left or right of the viewport. The actual
1524              position of the block relative to ZFX depends on the value
1525              assigned to the Zero Field Positioning Mode parameter, ZFP. The
1526              default value is 0.5.
1527
1528       ZFY - Zero Field Text Block Y Coordinate - Real
1529              ZFY establishes the Y coordinate of the minimum vector graphics
1530              text block as a fraction of the viewport height.  Values less
1531              than 0.0 or greater than 1.0 are permissible and respectively
1532              represent regions below and above the viewport. The actual
1533              position of the block relative to ZFY depends on the value
1534              assigned to the Zero Field Positioning Mode parameter, ZFP. The
1535              default value is 0.5.
1536

SEE ALSO

1538       Online: vectors, vvectr, vvgetc, vvgeti, vvgetr, vvinit, vvrset,
1539       vvsetc, vvseti, vvsetr.  vvudmv, vvumxy, ncarg_cbind.
1540
1541       Hardcopy: NCAR Graphics Fundamentals, UNIX Version
1542
1544       Copyright (C) 1987-2009
1545       University Corporation for Atmospheric Research
1546       The use of this Software is governed by a License Agreement.
1547
1548
1549
1550UNIX                              April 1993            Vectors_params(3NCARG)
Impressum