1Streamlines_params(3NCARG)       NCAR GRAPHICS      Streamlines_params(3NCARG)
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NAME

6       Streamlines_params - This document briefly describes all Streamlines
7       internal parameters.
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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, and the intrinsic
13       type of the parameter.
14
15       AGD - Arrow Placement Grid Increment - Integer
16              This parameter allows you a degree of control over directional
17              arrowhead spacing in the field flow plot.  Streamlines allows a
18              maximum of one directional arrowhead for each grid box, where a
19              grid box is the space between adjacent integer grid coordinates
20              in the grid coordinate system along both dimensions. However,
21              Streamlines actually places an arrowhead only if both lower grid
22              indices, modulo the value of AGD, are equal to 0. If AGD is set
23              to 2, for instance, Streamlines places an arrowhead on the first
24              streamline to enter each grid box with even-numbered lower grid
25              indices.
26
27              If the transformation pipeline is everywhere linear from grid
28              coordinate space to NDC space, then the spacing of the
29              arrowheads should be more or less uniform over the field flow
30              plot. However, if there is a non-linearity anywhere in the
31              pipeline, the arrowheads will probably be more crowded in some
32              areas than in others. The default value of AGD is 2.
33
34       AMD - Arrow Head Minimum Distance - Real
35              AMD allows you to specify, as a fraction of the viewport width,
36              a minimum distance between adjacent directional arrowheads along
37              a single streamline. If the data grid is transformed in such a
38              way that adjacent grid cells become very close in NDC space, as
39              for instance in many map projections near the poles, you can use
40              this parameter to help reduce the otherwise cluttered appearance
41              of these regions of the plot. Note that currently, whenever AMD
42              has a positive value, the first arrowhead that would otherwise
43              be drawn for each streamline is always eliminated. If AMD is
44              less than or equal to 0.0, then no arrowheads are eliminated.
45              The default value of AMD is 0.0.
46
47       ARL - Arrow Head Length - Real
48              ARL defines the length of each of the two lines used to create
49              the directional arrow head. If the parameter GBS is set to 0,
50              ARL has units "fraction of viewport width"; if GBS is set to 1,
51              ARL has the units "fraction of grid box width".  The default
52              value of ARL is 0.012 when GBS has the value 0 and 0.33 when GBS
53              has the value 1. Setting GBS causes ARL to be reset to its
54              appropriate default value.
55
56       CDS - Critical Displacement Multiplier - Real
57              CDS specifies the minimum amount the streamline must grow as a
58              multiple of the basic differential step size each time the
59              stream progress is checked in order for the streamline not to be
60              terminated. The nominal differential step size is specified by
61              DFM in NDC space, and the progress is checked each CKP
62              iterations. Points of convergence or divergence typically cause
63              stream growth to diminish and the streamline eventually to be
64              terminated. The default value of CDS is 2.0, meaning that any
65              time a streamline does not increase in length a minimum of
66              2.0*DFM in NDC over the previous check, it is discontinued and a
67              new streamline is begun if possible.
68
69       CKP - Check Progress Iteration Count - Integer
70              The parameter CKP specifies the number of iterations through the
71              streamline building loop between each check of the streamline
72              growth. If the distance between current position of the
73              streamline and the position saved at the time of the previous
74              check is less than a minimum amount, defined as the value of CDS
75              times the value of DFM in NDC space, then the current streamline
76              is terminated and a new one begun if possible. The default value
77              of CKP is 35.
78
79       CKX - Check Crossover Iteration Count - Integer
80              CKX specifies the number of iterations through the streamline
81              building loop between checks for streamline crossover, that is,
82              one streamline growing closer than a certain distance (as
83              specified by the parameter SSP) to previously created
84              streamline. A negative value of CKX causes Streamlines to check
85              for crossover only when a new grid box is entered. At each
86              crossover check, the current streamline position is compared
87              with a sampling of previous streamline positions retained in an
88              internal circular list. This list is currently fixed to a length
89              of 750. Since up to this number of comparisons are performed at
90              each crossover check, the frequency with which these checks are
91              performed can have a noticeable impact on performance. By
92              default, CKX has the value -99, causing Streamlines to check for
93              crossover only on entrance to a new grid box.
94
95       CYK - Cyclical Data Flag - Integer
96              Use this parameter to specify that the data in the vector field
97              arrays is cyclical: that is, it repeats with a period of M-1 (M,
98              the input parameter to STINIT) along the first dimensional axis.
99              If the flag is set on, Streamlines checks to see if the field
100              data meet certain criteria. If they do, an internal cyclical
101              flag is set, causing the normalized vector interpolation
102              routines to consider data from the opposite ends of the dataset
103              when interpolating near the first dimensional dataset
104              boundaries. If the criteria are not met, Streamlines sets an
105              error flag, retrievable by the user through the parameter ERR.
106              Processing, however, continues without interruption, except that
107              Streamlines now interpolates (as it would ordinarily) near the
108              first dimensional end points without consideration of data at
109              the opposite end. The data must pass the following test in order
110              to be deemed cyclical: for each subscript value along the second
111              dimensional axis, the first element and the last element along
112              the first dimensional axis must be identical. A value of 0 for
113              CYK means that the data is to be considered non-cyclical; any
114              other value means that Streamlines should test for the cyclical
115              condition.  You must initialize Streamlines with a call to
116              STINIT after modifying this parameter. The default value of CYK
117              is 0.
118
119       CPM - Compatibility Mode - Integer
120              Controls the degree of compatibility between versions of the
121              Streamlines utility prior to NCAR Graphics 3.2 and the current
122              version. You can independently control three behaviors using the
123              nine settings provided:
124
125              ·      use of STRMLN input parameters;
126
127              ·      use of variables contained in the common blocks STR02 and
128                     STR03;
129
130              ·      use of the old coordinate mapping routines, FX and FY.
131
132              Note, however, that when using the Version 3.2 entry points
133              STINIT and STREAM, only the third behavior option has any
134              meaning.
135
136              When CPM is set to 0, its default value, the Streamlines
137              utility´s behavior varies depending on whether you access it
138              through one of the pre-Version 3.2 entry points (STRMLN and
139              EZSTRM), or through the STINIT/STREAM interface. Otherwise,
140              positive values result in invocation of the older coordinate
141              mapping routines (FX and FY). Negative values cause the Version
142              3.2 mapping routines to be used instead.  When using the pre-
143              Version 3.2 interface only, odd values of CPM cause the data
144              values in the common blocks, STR02 and STR03, to override
145              corresponding values initialized in the Version 3.2 STDATA block
146              data subroutine, or set by the user calling STSETx routines.
147              Values of CPM with absolute value less than or equal to two
148              cause the NSET argument to STRMLN to take precedence over the
149              SET parameter.
150
151              Here is a table of the nine settings of CPM and their effect on
152              the operation of the Streamlines utility:
153
154
155              Value   Use FX and FY            Use STR02,STR03   Use NSET
156              -----   -------------            ---------------   --------
157              -4      no                       no                no
158              -3      no                       yes               no
159              -2      no                       no                yes
160              -1      no                       yes               yes
161              0       old - yes;new - no (*)   yes               yes
162              1       yes                      yes               yes
163              2       yes                      no                yes
164              3       yes                      yes               no
165              4       yes                      no                no
166
167              (*) Old means EZSTRM or STRMLN entry point; new, STINIT/STREAM.
168              Only the first column is applicable to the behavior of the
169              STINIT/STREAM interface. See the strmln man page for more
170              detailed emulation information.
171
172       DFM - Streamline Differential Magnitude
173              DFM specifies the length of the differential magnitude step size
174              used by Streamlines. If the parameter GBS is set to 0 DFM has
175              units "fraction of viewport width"; if GBS is set to 1, DFM has
176              the units "fraction of grid box width". When the Version 3.2
177              mapping routines are used, DFM directly affects processing time
178              and the resulting plot precision. In general, smaller values of
179              DFM cause Streamlines to take more, smaller steps in the
180              construction of a streamline, resulting, within the limits of
181              the processor´s floating point resolution, in longer execution
182              times and a more precise plot.  Process memory requirements are
183              not affected. If the compatibility mode parameter is set such
184              that the older mapping routines, FX and FY, are invoked instead,
185              DFM no longer has any effect on the plot, since in this case the
186              step size is determined by the setting of the parameter VNL as a
187              fraction of the grid box width. The default value of DFM is 0.02
188              when GBS has the value 0 and 0.33 when GBS has the value 1.
189              Setting GBS causes DFM to be reset to its appropriate default
190              value.
191
192       GBS - Grid-Based Spacing - Real
193              The parameter GBS controls the interpretation of several
194              parameters that play a critical role in the appearance of the
195              streamline plot. These parameters are DFM, SSP, and ARL. When
196              GBS has the value 0, the values of these parameters are treated
197              as having units of "fraction of viewport width". If GBS has the
198              value 1, the values are treated as having the units of "fraction
199              of grid box width". Whenever you set GBS, the three affected
200              parameters are reset to default values appropriate to the units;
201              therefore you must set GBS prior to setting any non-default
202              values for DFM, SSP, or ARL. You may find that using the grid-
203              based spacing method causes Streamlines to adapt more gracefully
204              to variations in the density of the data grid. Currently, the
205              default value of GBS is 0; however, in the next release this may
206              change.
207
208       LWD - Streamline Linewidth - Real
209              LWD controls the linewidth used to draw the streamlines.  Note
210              that since the linewidth in NCAR Graphics is always calculated
211              relative to a unit linewidth that is dependent on the output
212              device, you may need to adjust the linewidth value depending on
213              the output conditions to obtain a pleasing plot. LWD affects the
214              linewidth of the directional arrowheads as well as the
215              streamlines themselves. The arrowhead length also increases
216              somewhat when the linewidth is greater than the default.
217              However, the arrowhead length parameter still affects the
218              length. The default is 1.0, specifying a device-dependent
219              minimum linewidth.
220
221       MAP - Map Transformation Code - Integer
222              MAP defines the mapping transformation between the data and user
223              coordinate space. For more information on coordinate mapping
224              transformations see the stuixy, stumxy, and stumta man pages, as
225              well as the description of the transformation type parameter,
226              TRT.  Three MAP parameter codes are reserved for pre-defined
227              transformations, as follows:
228
229              Value          Mapping transformation
230
231              0 (default)    Identity transformation between data and user
232                             coordinates: array indices of U and V are
233                             linearly related to user coordinates.  Note
234                             however that a non-linear transformation is still
235                             possible from user to NDC coordinates.
236
237              1              Ezmap transformation: first dimension indices of
238                             U and V are linearly related to longitude; second
239                             dimension indices are linearly related to
240                             latitude.
241
242              2              Polar to rectangular transformation: first
243                             dimension indices of U and V are linearly related
244                             to the radius; second dimension indices are
245                             linearly related to the angle in degrees.
246
247              If MAP has any other value, Streamlines invokes the user-
248              modifiable subroutines, STUMXY, STUIXY, and STUMTA to perform
249              the mapping. The default version of these routines simply
250              performs an identity mapping.  Note that, while the Streamlines
251              utility does not actually prohibit the practice, you are advised
252              not to use negative integers for user-defined mappings, since
253              other utilities in the NCAR Graphics toolkit attach a special
254              meaning to negative mapping codes.
255
256              For all the predefined mappings, the linear relationship between
257              the grid array indices and the data coordinate system is
258              established using the four parameters, XC1, XCM, YC1, and YCN.
259              The X parameters define a mapping for the first and last indices
260              of the first dimension of the data arrays, and the Y parameters
261              do the same for the second dimension. If MAP is set to a value
262              of one, you need to be careful to ensure that the SET parameter
263              is given a value of zero, since the Ezmap routines require a
264              specific user coordinate space for each projection type, and
265              internally call the SET routine to define the user to NDC
266              mapping.  Otherwise, you may choose whether or not to issue a
267              SET call prior to calling STINIT, modifying the value of SET as
268              required. See the description of the parameter, TRT, and the man
269              pages, stumxy, stuixy, and stumta for more information.
270
271       MSK - Mask To Area Map Flag - Integer
272              Use this parameter to control masking of streamlines to an
273              existing area map created by routines in the Areas utility.
274              When MSK is greater than 0, masking is enabled and an area map
275              must be set up before calling STREAM. The area map array and, in
276              addition, the name of a user-definable masked drawing routine,
277              must be passed as input parameters to STREAM. There are two
278              states for the MSK parameter, as follows:
279
280              Value          Effect
281
282              <= 0 (default) No streamline masking.
283
284              >0             The subroutine ARDRLN is called internally to
285                             decompose the streamlines into segments contained
286                             entirely within a single area group. ARDRLN calls
287                             the user-definable masked drawing subroutine.
288
289              See the man page, stumsl, for further information on the user-
290              definable masked drawing subroutine.
291
292       PLR - Polar Input Mode - Integer
293              When PLR is greater than zero, the vector component arrays are
294              considered to contain the field data in polar coordinate form:
295              the U array is treated as containing the vector magnitude and
296              the V array as containing the vector angle. Be careful not to
297              confuse the PLR parameter with the MAP parameter polar
298              coordinate mode. The MAP parameter relates to the location of
299              the vector, not its value. Here is a table of values for PLR:
300
301              Value          Meaning
302
303              0 (default)    U and V arrays contain data in cartesian
304                             component form.
305
306              1              U array contains vector magnitudes; V array
307                             contains vector angles in degrees.
308
309              2              U array contain vector magnitudes; V array
310                             contains vector angles in radians.
311
312              You must initialize Streamlines with a call to STINIT after
313              modifying this parameter.
314
315       SET - SET Call Flag - Integer
316              Give SET the value 0 to inhibit the SET call STINIT performs by
317              default. Arguments 5-8 of a SET call made by the user must be
318              consistent with the ranges of the user coordinates expected by
319              Streamlines. This is determined by the mapping from grid to data
320              coordinates as specified by the values of the parameters XC1,
321              XCM, YC1, YCN, and also by the mapping from data to user
322              coordinates established by the MAP parameter. You must
323              initialize Streamlines with a call to STINIT after modifying
324              this parameter. The default value of SET is 1.
325
326       SGD - Stream Starting Grid Increment - Integer
327              This parameter gives you a degree of control over the number and
328              density of streamlines in the field flow plot.  The Streamlines
329              utility never begins a streamline in any grid box that has
330              previously had a streamline pass through it, where a grid box is
331              defined as the space between adjacent integer grid coordinates
332              in the grid coordinate system along both dimensions. By setting
333              SGD to a value greater than 1, you can reduce the number of grid
334              boxes initially eligible for starting a streamline. A grid box
335              is considered initially eligible for starting a streamline only
336              if both the lesser indices that establish the grid box, modulo
337              the value of SGD, equal 0. If SGD is set to 2, for instance,
338              every grid box with even-numbered lower grid indices would be
339              initially eligible for starting a streamline. As the streamlines
340              grow and pass through grid boxes that were initially eligible,
341              these boxes too are marked ineligible, further reducing the
342              boxes where a stream can be started.
343
344              If the transformation pipeline is everywhere linear from grid
345              coordinate space to NDC space, then this scheme for starting
346              streamlines usually produces a more or less uniform spacing of
347              the streamlines over the field flow plot. However, if there are
348              non-linear transforms anywhere in the pipeline, the streamlines
349              will probably be more crowded in some areas than in others.
350              Future enhancements to the Streamlines utility are expected to
351              address this issue, and also perhaps to provide options for
352              intentional non-uniform spacing based on flow intensity. The
353              default value of SGD is 2.
354
355       SSP - Streamline Spacing Value - Real
356              The streamline spacing parameter establishes the minimum
357              distance a streamline in progress is allowed to approach
358              existing streamlines before being terminated. If the parameter
359              GBS is set to 0, SSP has units "fraction of viewport width"; if
360              GBS is set to 1, SSP has the units "fraction of grid box width".
361              In general, within either system of units, larger values of SSP
362              increase the distance between streamlines, and have a tendency
363              to create more, but shorter stream lines. The spacing is only
364              checked at intervals, so streamlines sometimes approach closer
365              than the specified distance. The checking frequency is
366              adjustable using the streamline crossover checking parameter,
367              CKX. The streamline starting grid increment parameter, SGD, also
368              affects the overall streamline density. The default value of SSP
369              is 0.015 when GBS has the value 0 and 0.5 when GBS has the value
370              1. Setting GBS causes SSP to be reset to its appropriate default
371              value.
372
373       SST - Streamline Statistics Output Flag - Integer
374              If SST is set to one, STREAM writes a summary of its operations
375              to the default logical output unit, including the number of
376              streamlines plotted and the total differential step count. Here
377              is a sample of the output:
378
379                 STREAM Statistics
380                                 Streamlines plotted:  119
381                       Total differential step count:  2903
382
383              The differential step count actually counts the number of
384              iterations through the main streamline construction loop, and
385              can be used to help gauge the trade-offs between the increased
386              processing time required for smaller differential step sizes and
387              the resulting differences in plot quality.
388
389       SVF - Special Value Flag - Integer
390              The special value flag controls special value processing for the
391              U and V vector component data arrays. Special values may appear
392              in either the U or V array or in both of them. When any of the
393              four points surrounding the current streamline end contain a
394              special value, the streamline is terminated, and a new one
395              started, if possible. Streamlines allows special value
396              processing to be turned on or off, as follows:
397
398              Value          Effect
399
400              0 (default)    Neither the U nor the V array is examined for
401                             special values
402
403              non 0          Whenever the streamline under construction enters
404                             a new grid box, the U and V array values at each
405                             corner of the box are examined for special
406                             values. The interpolation method parameter, TRP,
407                             is overridden, causing Streamlines to use bi-
408                             linear interpolation only.
409
410              The U and V special values are defined by setting parameters USV
411              and VSV. Streamlines only uses bi-linear interpolation when
412              special value processing is in effect, because the Bessel
413              interpolation method quadruples the requirement for good data
414              points (from 4 to 16) surrounding the current stream end point.
415              You must initialize Streamlines with a call to STINIT after
416              modifying this parameter.
417
418       TRP - Interpolation Method - Integer
419              Use TRP to control which of two interpolation methods
420              Streamlines should use in determining the normalized flow
421              components for each point in the streamline. The choices are as
422              follows:
423
424              Value          Interpolation Method
425
426              0 (default)    Use the 16-point Bessel interpolation method
427                             where possible; otherwise, near the data set
428                             boundaries use 12, 9 or 4 point interpolation
429                             methods, depending on the situation.
430
431              non 0          Use 4-point bi-linear interpolation at all
432                             points.
433
434              Note that Streamlines forces use of the 4-point bi-linear
435              interpolation method if the SVF parameter is set to turn on
436              special value processing.
437
438       TRT - Transformation Type - Integer
439              The transformation type parameter, TRT, qualifies the mapping
440              transformation specified by the MAP parameters, as follows:
441
442              Value          Effect
443
444              -1             Direction, magnitude, and location are all
445                             transformed. This option is not currently
446                             supported by any of the pre-defined coordinate
447                             system mappings.
448
449              0              Only location is transformed
450
451              1 (default)    Direction and location are transformed
452
453              This parameter allows you to distinguish between a system that
454              provides a mapping of location only into an essentially
455              cartesian space, and one in which the space itself mapped. To
456              understand the difference, using polar coordinates as an
457              example, imagine a set of wind speed monitoring units located on
458              a radial grid around some central point such as an airport
459              control tower. Each unit´s position is defined in terms of its
460              distance from the tower and its angular direction from due east.
461              However, the data collected by each monitoring unit is
462              represented as conventional eastward and northward wind
463              components.  Assuming the towers´s location is at a moderate
464              latitude, and the monitoring units are reasonably ´local´, this
465              is an example of mapping a radially defined location into a
466              nearly cartesian space (i.e. if the northward components were
467              all set to 0.0, the streamlines defined by the eastward
468              components would all be parallel straight lines.  One would set
469              MAP to two (for the polar transformation) and TRT to zero to
470              model this data on a plot generated by the Streamlines utility.
471
472              On the other hand, picture a set of wind data, again given as
473              eastward and northward wind components, but this time the center
474              of the polar map is actually one of the earth´s poles. In this
475              case, the eastward components do not point in a single
476              direction; instead they outline a series of concentric circles
477              around the pole. This is a space mapping transformation: one
478              would again set MAP to two, but TRT would be set to one to
479              transform both direction and location.
480
481              Changing the setting of this parameter affects the end results
482              only when a non-uniform non-linear mapping occurs at some point
483              in the transformation pipeline. For this discussion a uniform
484              linear transformation is defined as one which satisfies the
485              following equations:
486
487                 x_out = x_offset + scale_constant * x_in
488                 y_out = y_offset + scale_constant * y_in
489
490              If scale_constant is not the same for both equations then the
491              mapping is non-uniform.
492
493              This option is currently implemented only for the pre-defined
494              MAP parameter codes, 0 and 2, the identity mapping and the polar
495              coordinate mapping. However, it operates on a different stage of
496              the transformation pipeline in each case. The polar mapping is
497              non-linear from data to user coordinates. The identity mapping,
498              even though necessarily linear over the data to user space
499              mapping, can have a non-uniform mapping from user to NDC space,
500              depending on the values given to the input parameters of the SET
501              call. This will be the case whenever the LL input parameter
502              specifies a logarithmic scaling or the viewport and the user
503              coordinate boundaries do not have the same aspect ratio. Thus
504              for a MAP value of 2, TRT affects the mapping between data and
505              user space, whereas for MAP set to 0, TRT influences the mapping
506              between user and NDC space.
507
508       USV - U Array Special Value - Real
509              USV is the U vector component array special value. It is a value
510              outside the range of the normal data used to indicate that there
511              is no valid data for this grid location. When the special value
512              flag parameter, SVF, is non-zero, each time a streamline enters
513              a new cell Streamlines will check for this special value in the
514              U array at each of the four corners of the grid box. Anytime the
515              special value is discovered, the current streamline is
516              terminated and a new one started if possible. The default value
517              given to USV is 1.0 * 10**12.
518
519       VNL - Vector Normalization Value - Real
520              The parameter, VNL, determines the value Streamlines uses to
521              normalize the vector flow field, before beginning the streamline
522              construction loop. When Streamlines is used with the pre-Version
523              3.2 mapping routines, FX and FY, the value of VNL determines the
524              step size in the grid coordinate system used to construct the
525              streamlines, as a fraction of the grid box size. When using FX
526              and FY, smaller values of VNL result in smaller steps, more
527              processing time and, within the limits of the processor´s
528              floating point accuracy, a higher precision plot. However, if
529              the mapping has non-linearities, the grid size does not remain
530              constant over the transformation and the step size can vary
531              greatly, resulting in discontinuities in certain areas of the
532              plot.
533
534              Streamline´s new mapping routines define the streamline
535              differential magnitude in NDC space, ensuring a constant step
536              size over the whole plot, notwithstanding any non-linearity in
537              the transformation. When using the new mapping routines, the
538              parameter DFM controls the step size in NDC space, and VNL is
539              not adjustable by the user. (See the discussion of the
540              compatibility mode parameter, CPM, for a discussion of how to
541              switch between the old and new mapping routines.) The default
542              value of VNL is 0.33.
543
544       VPB - Viewport Bottom - Real
545              The parameter VPB has an effect only when SET is non-zero,
546              specifying that Streamlines should do the call to SET. It
547              defines a minimum boundary value for the bottom edge of the
548              viewport in NDC space, and is constrained to a value between 0.0
549              and 1.0. It must be less than the value of the Viewport Top
550              parameter, VPT. The actual value of the viewport bottom edge
551              used in the plot may be greater than the value of VPB, depending
552              on the setting of the Viewport Shape parameter, VPS.  You must
553              initialize Streamlines with a call to STINIT after modifying
554              this parameter. The default value of VPB is 0.05.
555
556       VPL - Viewport Left - Real
557              The parameter VPL has an effect only when SET is non-zero,
558              specifying that Streamlines should do the call to SET. It
559              defines a minimum boundary value for the left edge of the
560              viewport in NDC space, and is constrained to a value between 0.0
561              and 1.0. It must be less than the value of the Viewport Right
562              parameter, VPR. The actual value of the viewport left edge used
563              in the plot may be greater than the value of VPL, depending on
564              the setting of the Viewport Shape parameter, VPS.  You must
565              initialize Streamlines with a call to STINIT after modifying
566              this parameter.  The default value of VPL is 0.05.
567
568       VPR - Viewport Right - Real
569              The parameter VPR has an effect only when SET is non-zero,
570              specifying that Streamlines should do the call to SET. It
571              defines a maximum boundary value for the right edge of the
572              viewport in NDC space, and is constrained to a value between 0.0
573              and 1.0. It must be greater than the value of the Viewport Left
574              parameter, VPL. The actual value of the viewport right edge used
575              in the plot may be less than the value of VPR, depending on the
576              setting of the Viewport Shape parameter, VPS.  You must
577              initialize Streamlines with a call to STINIT after modifying
578              this parameter.  The default value of VPR is 0.95.
579
580       VPS - Viewport Shape - Real
581              The parameter VPS has an effect only when SET is non-zero,
582              specifying that Streamlines should do the call to SET; it
583              defines the desired viewport shape, as follows:
584
585              Value          Effect
586
587              <0.0           The absolute value of VPS specifies the shape to
588                             use for the viewport, as the ratio of the
589                             viewport width to its height,
590
591              0.0            The viewport completely fills the area defined by
592                             the boundaries specifiers, VPL, VPR, VPB, VPT
593
594              >0.0,<1.0 (0.25,default)
595                             Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape
596                             if MIN(R, 1.0/R) is greater than VPS. Otherwise
597                             determine the shape as when VPS is equal to 0.0.
598
599              >= 1.0         Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape
600                             if MAX(R, 1.0/R) is less than VPS. Otherwise make
601                             the viewport a square.
602
603              The viewport, whatever its final shape, is centered in, and made
604              as large as possible in, the area specified by the parameters
605              VPB, VPL, VPR, and VPT. You must initialize Streamlines with a
606              call to STINIT after modifying this parameter.
607
608       VPT - Viewport Top - Real
609              The parameter VPT has an effect only when SET is non-zero,
610              specifying that Streamlines should do the call to SET. It
611              defines a maximum boundary value for the top edge of the
612              viewport in NDC space, and is constrained to a value between 0.0
613              and 1.0. It must be greater than the value of the Viewport
614              Bottom parameter, VPB. The actual value of the viewport top edge
615              used in the plot may be less than the value of VPT, depending on
616              the setting of the Viewport Shape parameter, VPS.  You must
617              initialize Streamlines with a call to STINIT after modifying
618              this parameter.  The default value of VPT is 0.95.
619
620       VSV - V Array Special Value - Real
621              VSV is the V vector component array special value. It is a value
622              outside the range of the normal data used to indicate that there
623              is no valid data for this grid location. When the special value
624              flag parameter, SVF, is non-zero, each time a streamline enters
625              a new cell Streamlines will check for this special value in the
626              V array at each of the four corners of the grid box.  Anytime
627              the special value is discovered, the current streamline is
628              terminated and a new one started if possible.  You must
629              initialize Streamlines with a call to STINIT after modifying
630              this parameter.  The default value given to VSV is 1.0 * 10**12.
631
632       WDB - Window Bottom - Real
633              When STINIT does the call to SET, the parameter WDB is used to
634              determine argument number 7, the user Y coordinate at the bottom
635              of the window. If WDB is not equal to WDT, WDB is used. If WDB
636              is equal to WDT, but YC1 is not equal to YCN, then YC1 is used.
637              Otherwise, the value 1.0 is used.  You must initialize
638              Streamlines with a call to STINIT after modifying this
639              parameter.  The default value of WDB is 0.0.
640
641       WDL - Window Left - Real
642              When STINIT the call to SET, the parameter WDL is used to
643              determine argument number 5, the user X coordinate at the left
644              edge of the window. If WDL is not equal to WDR, WDL is used. If
645              WDL is equal to WDR, but XC1 is not equal to XCM, then XC1 is
646              used. Otherwise, the value 1.0 is used. You must initialize
647              Streamlines with a call to STINIT after modifying this
648              parameter.  The default value of WDL is 0.0.
649
650       WDR - Window Right - Real
651              When STINIT does the call to SET, the parameter WDR is used to
652              determine argument number 6, the user X coordinate at the right
653              edge of the window. If WDR is not equal to WDL, WDR is used. If
654              WDR is equal to WDL, but XCM is not equal to XC1, then XCM is
655              used.  Otherwise, the value of the STINIT input parameter, M,
656              converted to a real, is used.  You must initialize Streamlines
657              with a call to STINIT after modifying this parameter.  The
658              default value of WDR is 0.0.
659
660       WDT - Window Top - Real
661              When STINIT does the call to SET, the parameter WDB is used to
662              determine argument number 8, the user Y coordinate at the top of
663              the window. If WDT is not equal to WDB, WDT is used. If WDT is
664              equal to WDB, but YCN is not equal to YC1 then YCN is used.
665              Otherwise, the value of the STINIT input parameter, N, converted
666              to a real, is used.  You must initialize Streamlines with a call
667              to STINIT after modifying this parameter.  The default value of
668              WDT is 0.0.
669
670       XC1 - X Coordinate at Index 1 - Real
671              The parameter XC1 specifies the X coordinate value that
672              corresponds to a value of 1 for the first subscript of the U and
673              V, vector field component arrays. Together with XCM, YC1, and
674              YCN it establishes the mapping from grid coordinate space to
675              data coordinate space. If XC1 is equal to XCM, 1.0 will be used.
676              You must initialize Streamlines with a call to STINIT after
677              modifying this parameter.  The default value of XC1 is 0.0.
678
679       XCM - X Coordinate at Index M - Real
680              The parameter XCM specifies the X coordinate value that
681              corresponds to the value of the STINIT input parameter, M, for
682              the first subscript of the U and V vector component arrays.
683              Together with XC1, YC1, and YCN it establishes the mapping from
684              grid coordinate space to data coordinate space. If XC1 is equal
685              to XCM, the value of M, converted to a real, will be used. You
686              must initialize Streamlines with a call to STINIT after
687              modifying this parameter.  The default value of XCM is 0.0
688
689       YC1 - Y Coordinate at Index 1 - Real
690              The parameter YC1 specifies the Y coordinate value that
691              corresponds to a value of 1 for the first subscript of the U, V,
692              vector component arrays as well as for the P scalar data array,
693              if used. Together with YCN, XC1, and XCM it establishes the
694              mapping from grid coordinate space to data coordinate space. If
695              YC1 is equal to YCN, 1.0 will be used.  You must initialize
696              Streamlines with a call to STINIT after modifying this
697              parameter.  The default value of YC1 is 0.0
698
699       YCN - Y Coordinate at Index N - Real
700              The parameter YCN specifies the Y coordinate value that
701              corresponds to the value of the STINIT input parameter, N, for
702              the second subscript of the U and V vector component arrays as
703              well as the P scalar data array, if used.  Together with YC1,
704              XC1, and XCM it establishes the mapping from grid coordinate
705              space to data coordinate space. If YC1 is equal to YCN, the
706              value of N, converted to a real, will be used. You must
707              initialize Streamlines with a call to STINIT after modifying
708              this parameter.  The default value of YCN is 0.0
709
710       ZFC - Zero Field Text Block Color - Integer
711              If ZFC is greater or equal to zero, it specifies the GKS color
712              index to use to color the Zero Field text block.  Otherwise the
713              Zero Field text block is colored using the current GKS text
714              color index. The default value of ZFC is -1.
715
716       ZFP - Zero Field Text Block Positioning Mode - Integer
717              The ZFP parameter allows you to justify, using any of the 9
718              standard justification modes, the Zero Field text block unit
719              with respect to the position established by the parameters, ZFX
720              and ZFY The position modes are supported as follows:
721
722              Mode           Justification
723
724              -4             The lower left corner of the text block is
725                             positioned at ZFX, ZFY.
726
727              -3             The center of the bottom edge is positioned at
728                             ZFX, ZFY.
729
730              -2             The lower right corner is positioned at ZFX, ZFY.
731
732              -1             The center of the left edge is positioned at ZFX,
733                             ZFY.
734
735              0 (default)    The text block is centered along both axes at
736                             ZFX, ZFY.
737
738              1              The center of the right edge is positioned at
739                             ZFX, ZFY.
740
741              2              The top left corner is positioned at ZFX, ZFY.
742
743              3              The center of the top edge is positioned at ZFX,
744                             ZFY.
745
746              4              The top right corner is positioned at ZFX, ZFY.
747
748       ZFS - Zero Field Text Block Character Size - Real
749              ZFS specifies the size of the characters used in the Zero Field
750              graphics text block as a fraction of the viewport width. The
751              default value is 0.033.
752
753       ZFT - Zero Field Text String - Character* 36
754              Use ZFT to modify the text of the Zero Field text block.  The
755              Zero Field text block may appear whenever the U and V vector
756              component arrays contain data such that all the grid points
757              otherwise eligible for plotting contain zero magnitude vectors.
758              Currently the string length is limited to 36 characters. Set ZFT
759              to a single space (´ ´) to prevent the text from being
760              displayed. The default value for the text is ´Zero Field´.
761
762       ZFX - Zero Field Text Block X Coordinate - Real
763              ZFX establishes the X coordinate of the Zero Field graphics text
764              block as a fraction of the viewport width. Values less than 0.0
765              or greater than 1.0 are permissible and respectively represent
766              regions to the left or right of the viewport. The actual
767              position of the block relative to ZFX depends on the value
768              assigned to the Zero Field Positioning Mode parameter, ZFP. The
769              default value is 0.5.
770
771       ZFY - Zero Field Text Block Y Coordinate - Real
772              ZFY establishes the Y coordinate of the minimum vector graphics
773              text block as a fraction of the viewport height.  Values less
774              than 0.0 or greater than 1.0 are permissible and respectively
775              represent regions below and above the viewport. The actual
776              position of the block relative to ZFY depends on the value
777              assigned to the Zero Field Positioning Mode parameter, ZFP. The
778              default value is 0.5.
779

SEE ALSO

781       Online: stgetc, stgeti, stgetr, stinit, stream, streamlines, strset,
782       stsetc, stseti, stsetr, stuixy, stumsl, stumta, stumxy, ncarg_cbind.
783
784       Hardcopy: NCAR Graphics Fundamentals, UNIX Version
785
787       Copyright (C) 1987-2009
788       University Corporation for Atmospheric Research
789
790       The use of this Software is governed by a License Agreement.
791
792
793
794UNIX                              March 1995        Streamlines_params(3NCARG)
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