1Streamlines_params(3NCARG) NCAR GRAPHICS Streamlines_params(3NCARG)
2
6 Streamlines_params - This document briefly describes all Streamlines
7 internal parameters.
8
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 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 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 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 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 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 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 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 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 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 · use of STRMLN input parameters;
126 · use of variables contained in the common blocks STR02 and
128 STR03;
129 · use of the old coordinate mapping routines, FX and FY.
131 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 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 Here is a table of the nine settings of CPM and their effect on
152 the operation of the Streamlines utility:
153 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 (*) 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 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 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 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 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 Value Mapping transformation
230 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 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 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 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 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 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 Value Effect
281 <= 0 (default) No streamline masking.
283 >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 See the man page, stumsl, for further information on the user-
290 definable masked drawing subroutine.
291 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 Value Meaning
302 0 (default) U and V arrays contain data in cartesian
304 component form.
305 1 U array contains vector magnitudes; V array
307 contains vector angles in degrees.
308 2 U array contain vector magnitudes; V array
310 contains vector angles in radians.
311 You must initialize Streamlines with a call to STINIT after
313 modifying this parameter.
314 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 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 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 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 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 STREAM Statistics
380 Streamlines plotted: 119
381 Total differential step count: 2903
382 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 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 Value Effect
399 0 (default) Neither the U nor the V array is examined for
401 special values
402 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 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 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 Value Interpolation Method
425 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 non 0 Use 4-point bi-linear interpolation at all
432 points.
433 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 TRT - Transformation Type - Integer
439 The transformation type parameter, TRT, qualifies the mapping
440 transformation specified by the MAP parameters, as follows:
441 Value Effect
443 -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 0 Only location is transformed
450 1 (default) Direction and location are transformed
452 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 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 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 x_out = x_offset + scale_constant * x_in
488 y_out = y_offset + scale_constant * y_in
489 If scale_constant is not the same for both equations then the
491 mapping is non-uniform.
492 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 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 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 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 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 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 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 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 Value Effect
586 <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 0.0 The viewport completely fills the area defined by
592 the boundaries specifiers, VPL, VPR, VPB, VPT
593 >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 >= 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 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 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 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 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 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 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 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 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 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 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 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 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 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 Mode Justification
723 -4 The lower left corner of the text block is
725 positioned at ZFX, ZFY.
726 -3 The center of the bottom edge is positioned at
728 ZFX, ZFY.
729 -2 The lower right corner is positioned at ZFX, ZFY.
731 -1 The center of the left edge is positioned at ZFX,
733 ZFY.
734 0 (default) The text block is centered along both axes at
736 ZFX, ZFY.
737 1 The center of the right edge is positioned at
739 ZFX, ZFY.
740 2 The top left corner is positioned at ZFX, ZFY.
742 3 The center of the top edge is positioned at ZFX,
744 ZFY.
745 4 The top right corner is positioned at ZFX, ZFY.
747 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 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 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 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
781 Online: stgetc, stgeti, stgetr, stinit, stream, streamlines, strset,
782 stsetc, stseti, stsetr, stuixy, stumsl, stumta, stumxy, ncarg_cbind.
783 Hardcopy: NCAR Graphics Fundamentals, UNIX Version
785
787 Copyright (C) 1987-2009
788 University Corporation for Atmospheric Research
789 The use of this Software is governed by a License Agreement.
791UNIX March 1995 Streamlines_params(3NCARG)