# ncl_streamlines_params - Man Page

This document briefly describes all Streamlines internal parameters.

## Description

Parameter descriptions follow, in alphabetical order. Each description begins with a line giving the three-character mnemonic name of the parameter, the phrase for which the mnemonic stands, and the intrinsic type of the parameter.

- AGD - Arrow Placement Grid Increment - Integer
This parameter allows you a degree of control over directional arrowhead spacing in the field flow plot. Streamlines allows a maximum of one directional arrowhead for each grid box, where a grid box is the space between adjacent integer grid coordinates in the grid coordinate system along both dimensions. However, Streamlines actually places an arrowhead only if both lower grid indices, modulo the value of AGD, are equal to 0. If AGD is set to 2, for instance, Streamlines places an arrowhead on the first streamline to enter each grid box with even-numbered lower grid indices.

If the transformation pipeline is everywhere linear from grid coordinate space to NDC space, then the spacing of the arrowheads should be more or less uniform over the field flow plot. However, if there is a non-linearity anywhere in the pipeline, the arrowheads will probably be more crowded in some areas than in others. The default value of AGD is 2.

- AMD - Arrow Head Minimum Distance - Real
AMD allows you to specify, as a fraction of the viewport width, a minimum distance between adjacent directional arrowheads along a single streamline. If the data grid is transformed in such a way that adjacent grid cells become very close in NDC space, as for instance in many map projections near the poles, you can use this parameter to help reduce the otherwise cluttered appearance of these regions of the plot. Note that currently, whenever AMD has a positive value, the first arrowhead that would otherwise be drawn for each streamline is always eliminated. If AMD is less than or equal to 0.0, then no arrowheads are eliminated. The default value of AMD is 0.0.

- ARL - Arrow Head Length - Real
ARL defines the length of each of the two lines used to create the directional arrow head. If the parameter GBS is set to 0, ARL has units "fraction of viewport width"; if GBS is set to 1, ARL has the units "fraction of grid box width". The default value of ARL is 0.012 when GBS has the value 0 and 0.33 when GBS has the value 1. Setting GBS causes ARL to be reset to its appropriate default value.

- CDS - Critical Displacement Multiplier - Real
CDS specifies the minimum amount the streamline must grow as a multiple of the basic differential step size each time the stream progress is checked in order for the streamline not to be terminated. The nominal differential step size is specified by DFM in NDC space, and the progress is checked each CKP iterations. Points of convergence or divergence typically cause stream growth to diminish and the streamline eventually to be terminated. The default value of CDS is 2.0, meaning that any time a streamline does not increase in length a minimum of 2.0*DFM in NDC over the previous check, it is discontinued and a new streamline is begun if possible.

- CKP - Check Progress Iteration Count - Integer
The parameter CKP specifies the number of iterations through the streamline building loop between each check of the streamline growth. If the distance between current position of the streamline and the position saved at the time of the previous check is less than a minimum amount, defined as the value of CDS times the value of DFM in NDC space, then the current streamline is terminated and a new one begun if possible. The default value of CKP is 35.

- CKX - Check Crossover Iteration Count - Integer
CKX specifies the number of iterations through the streamline building loop between checks for streamline crossover, that is, one streamline growing closer than a certain distance (as specified by the parameter SSP) to previously created streamline. A negative value of CKX causes Streamlines to check for crossover only when a new grid box is entered. At each crossover check, the current streamline position is compared with a sampling of previous streamline positions retained in an internal circular list. This list is currently fixed to a length of 750. Since up to this number of comparisons are performed at each crossover check, the frequency with which these checks are performed can have a noticeable impact on performance. By default, CKX has the value -99, causing Streamlines to check for crossover only on entrance to a new grid box.

- CYK - Cyclical Data Flag - Integer
Use this parameter to specify that the data in the vector field arrays is cyclical: that is, it repeats with a period of M-1 (M, the input parameter to STINIT) along the first dimensional axis. If the flag is set on, Streamlines checks to see if the field data meet certain criteria. If they do, an internal cyclical flag is set, causing the normalized vector interpolation routines to consider data from the opposite ends of the dataset when interpolating near the first dimensional dataset boundaries. If the criteria are not met, Streamlines sets an error flag, retrievable by the user through the parameter ERR. Processing, however, continues without interruption, except that Streamlines now interpolates (as it would ordinarily) near the first dimensional end points without consideration of data at the opposite end. The data must pass the following test in order to be deemed cyclical: for each subscript value along the second dimensional axis, the first element and the last element along the first dimensional axis must be identical. A value of 0 for CYK means that the data is to be considered non-cyclical; any other value means that Streamlines should test for the cyclical condition. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of CYK is 0.

- CPM - Compatibility Mode - Integer
Controls the degree of compatibility between versions of the Streamlines utility prior to NCAR Graphics 3.2 and the current version. You can independently control three behaviors using the nine settings provided:

- use of STRMLN input parameters;
- use of variables contained in the common blocks STR02 and STR03;
- use of the old coordinate mapping routines, FX and FY.

Note, however, that when using the Version 3.2 entry points STINIT and STREAM, only the third behavior option has any meaning.

When CPM is set to 0, its default value, the Streamlines utility´s behavior varies depending on whether you access it through one of the pre-Version 3.2 entry points (STRMLN and EZSTRM), or through the STINIT/STREAM interface. Otherwise, positive values result in invocation of the older coordinate mapping routines (FX and FY). Negative values cause the Version 3.2 mapping routines to be used instead. When using the pre-Version 3.2 interface only, odd values of CPM cause the data values in the common blocks, STR02 and STR03, to override corresponding values initialized in the Version 3.2 STDATA block data subroutine, or set by the user calling STSETx routines. Values of CPM with absolute value less than or equal to two cause the NSET argument to STRMLN to take precedence over the SET parameter.

Here is a table of the nine settings of CPM and their effect on the operation of the Streamlines utility:

Value Use FX and FY Use STR02,STR03 Use NSET ----- ------------- --------------- -------- -4 no no no -3 no yes no -2 no no yes -1 no yes yes 0 old - yes;new - no (*) yes yes 1 yes yes yes 2 yes no yes 3 yes yes no 4 yes no no (*) Old means EZSTRM or STRMLN entry point; new, STINIT/STREAM. Only the first column is applicable to the behavior of the STINIT/STREAM interface. See the strmln man page for more detailed emulation information.

- DFM - Streamline Differential Magnitude
DFM specifies the length of the differential magnitude step size used by Streamlines. If the parameter GBS is set to 0 DFM has units "fraction of viewport width"; if GBS is set to 1, DFM has the units "fraction of grid box width". When the Version 3.2 mapping routines are used, DFM directly affects processing time and the resulting plot precision. In general, smaller values of DFM cause Streamlines to take more, smaller steps in the construction of a streamline, resulting, within the limits of the processor´s floating point resolution, in longer execution times and a more precise plot. Process memory requirements are not affected. If the compatibility mode parameter is set such that the older mapping routines, FX and FY, are invoked instead, DFM no longer has any effect on the plot, since in this case the step size is determined by the setting of the parameter VNL as a fraction of the grid box width. The default value of DFM is 0.02 when GBS has the value 0 and 0.33 when GBS has the value 1. Setting GBS causes DFM to be reset to its appropriate default value.

- GBS - Grid-Based Spacing - Real
The parameter GBS controls the interpretation of several parameters that play a critical role in the appearance of the streamline plot. These parameters are DFM, SSP, and ARL. When GBS has the value 0, the values of these parameters are treated as having units of "fraction of viewport width". If GBS has the value 1, the values are treated as having the units of "fraction of grid box width". Whenever you set GBS, the three affected parameters are reset to default values appropriate to the units; therefore you must set GBS prior to setting any non-default values for DFM, SSP, or ARL. You may find that using the grid-based spacing method causes Streamlines to adapt more gracefully to variations in the density of the data grid. Currently, the default value of GBS is 0; however, in the next release this may change.

- LWD - Streamline Linewidth - Real
LWD controls the linewidth used to draw the streamlines. Note that since the linewidth in NCAR Graphics is always calculated relative to a unit linewidth that is dependent on the output device, you may need to adjust the linewidth value depending on the output conditions to obtain a pleasing plot. LWD affects the linewidth of the directional arrowheads as well as the streamlines themselves. The arrowhead length also increases somewhat when the linewidth is greater than the default. However, the arrowhead length parameter still affects the length. The default is 1.0, specifying a device-dependent minimum linewidth.

- MAP - Map Transformation Code - Integer
MAP defines the mapping transformation between the data and user coordinate space. For more information on coordinate mapping transformations see the stuixy, stumxy, and stumta man pages, as well as the description of the transformation type parameter, TRT. Three MAP parameter codes are reserved for pre-defined transformations, as follows:

- Value
Mapping transformation

- 0 (default)
Identity transformation between data and user coordinates: array indices of U and V are linearly related to user coordinates. Note however that a non-linear transformation is still possible from user to NDC coordinates.

- 1
Ezmap transformation: first dimension indices of U and V are linearly related to longitude; second dimension indices are linearly related to latitude.

- 2
Polar to rectangular transformation: first dimension indices of U and V are linearly related to the radius; second dimension indices are linearly related to the angle in degrees.

If MAP has any other value, Streamlines invokes the user-modifiable subroutines, STUMXY, STUIXY, and STUMTA to perform the mapping. The default version of these routines simply performs an identity mapping. Note that, while the Streamlines utility does not actually prohibit the practice, you are advised not to use negative integers for user-defined mappings, since other utilities in the NCAR Graphics toolkit attach a special meaning to negative mapping codes.

For all the predefined mappings, the linear relationship between the grid array indices and the data coordinate system is established using the four parameters, XC1, XCM, YC1, and YCN. The X parameters define a mapping for the first and last indices of the first dimension of the data arrays, and the Y parameters do the same for the second dimension. If MAP is set to a value of one, you need to be careful to ensure that the SET parameter is given a value of zero, since the Ezmap routines require a specific user coordinate space for each projection type, and internally call the SET routine to define the user to NDC mapping. Otherwise, you may choose whether or not to issue a SET call prior to calling STINIT, modifying the value of SET as required. See the description of the parameter, TRT, and the man pages, stumxy, stuixy, and stumta for more information.

- MSK - Mask To Area Map Flag - Integer
Use this parameter to control masking of streamlines to an existing area map created by routines in the Areas utility. When MSK is greater than 0, masking is enabled and an area map must be set up before calling STREAM. The area map array and, in addition, the name of a user-definable masked drawing routine, must be passed as input parameters to STREAM. There are two states for the MSK parameter, as follows:

- Value
Effect

- <= 0 (default)
No streamline masking.

- >0
The subroutine ARDRLN is called internally to decompose the streamlines into segments contained entirely within a single area group. ARDRLN calls the user-definable masked drawing subroutine.

See the man page, stumsl, for further information on the user-definable masked drawing subroutine.

- PLR - Polar Input Mode - Integer
When PLR is greater than zero, the vector component arrays are considered to contain the field data in polar coordinate form: the U array is treated as containing the vector magnitude and the V array as containing the vector angle. Be careful not to confuse the PLR parameter with the MAP parameter polar coordinate mode. The MAP parameter relates to the location of the vector, not its value. Here is a table of values for PLR:

- Value
Meaning

- 0 (default)
U and V arrays contain data in cartesian component form.

- 1
U array contains vector magnitudes; V array contains vector angles in degrees.

- 2
U array contain vector magnitudes; V array contains vector angles in radians.

You must initialize Streamlines with a call to STINIT after modifying this parameter.

- SET - SET Call Flag - Integer
Give SET the value 0 to inhibit the SET call STINIT performs by default. Arguments 5-8 of a SET call made by the user must be consistent with the ranges of the user coordinates expected by Streamlines. This is determined by the mapping from grid to data coordinates as specified by the values of the parameters XC1, XCM, YC1, YCN, and also by the mapping from data to user coordinates established by the MAP parameter. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of SET is 1.

- SGD - Stream Starting Grid Increment - Integer
This parameter gives you a degree of control over the number and density of streamlines in the field flow plot. The Streamlines utility never begins a streamline in any grid box that has previously had a streamline pass through it, where a grid box is defined as the space between adjacent integer grid coordinates in the grid coordinate system along both dimensions. By setting SGD to a value greater than 1, you can reduce the number of grid boxes initially eligible for starting a streamline. A grid box is considered initially eligible for starting a streamline only if both the lesser indices that establish the grid box, modulo the value of SGD, equal 0. If SGD is set to 2, for instance, every grid box with even-numbered lower grid indices would be initially eligible for starting a streamline. As the streamlines grow and pass through grid boxes that were initially eligible, these boxes too are marked ineligible, further reducing the boxes where a stream can be started.

If the transformation pipeline is everywhere linear from grid coordinate space to NDC space, then this scheme for starting streamlines usually produces a more or less uniform spacing of the streamlines over the field flow plot. However, if there are non-linear transforms anywhere in the pipeline, the streamlines will probably be more crowded in some areas than in others. Future enhancements to the Streamlines utility are expected to address this issue, and also perhaps to provide options for intentional non-uniform spacing based on flow intensity. The default value of SGD is 2.

- SSP - Streamline Spacing Value - Real
The streamline spacing parameter establishes the minimum distance a streamline in progress is allowed to approach existing streamlines before being terminated. If the parameter GBS is set to 0, SSP has units "fraction of viewport width"; if GBS is set to 1, SSP has the units "fraction of grid box width". In general, within either system of units, larger values of SSP increase the distance between streamlines, and have a tendency to create more, but shorter stream lines. The spacing is only checked at intervals, so streamlines sometimes approach closer than the specified distance. The checking frequency is adjustable using the streamline crossover checking parameter, CKX. The streamline starting grid increment parameter, SGD, also affects the overall streamline density. The default value of SSP is 0.015 when GBS has the value 0 and 0.5 when GBS has the value 1. Setting GBS causes SSP to be reset to its appropriate default value.

- SST - Streamline Statistics Output Flag - Integer
If SST is set to one, STREAM writes a summary of its operations to the default logical output unit, including the number of streamlines plotted and the total differential step count. Here is a sample of the output:

STREAM Statistics Streamlines plotted: 119 Total differential step count: 2903

The differential step count actually counts the number of iterations through the main streamline construction loop, and can be used to help gauge the trade-offs between the increased processing time required for smaller differential step sizes and the resulting differences in plot quality.

- SVF - Special Value Flag - Integer
The special value flag controls special value processing for the U and V vector component data arrays. Special values may appear in either the U or V array or in both of them. When any of the four points surrounding the current streamline end contain a special value, the streamline is terminated, and a new one started, if possible. Streamlines allows special value processing to be turned on or off, as follows:

- Value
Effect

- 0 (default)
Neither the U nor the V array is examined for special values

- non 0
Whenever the streamline under construction enters a new grid box, the U and V array values at each corner of the box are examined for special values. The interpolation method parameter, TRP, is overridden, causing Streamlines to use bi-linear interpolation only.

The U and V special values are defined by setting parameters USV and VSV. Streamlines only uses bi-linear interpolation when special value processing is in effect, because the Bessel interpolation method quadruples the requirement for good data points (from 4 to 16) surrounding the current stream end point. You must initialize Streamlines with a call to STINIT after modifying this parameter.

- TRP - Interpolation Method - Integer
Use TRP to control which of two interpolation methods Streamlines should use in determining the normalized flow components for each point in the streamline. The choices are as follows:

- Value
Interpolation Method

- 0 (default)
Use the 16-point Bessel interpolation method where possible; otherwise, near the data set boundaries use 12, 9 or 4 point interpolation methods, depending on the situation.

- non 0
Use 4-point bi-linear interpolation at all points.

Note that Streamlines forces use of the 4-point bi-linear interpolation method if the SVF parameter is set to turn on special value processing.

- TRT - Transformation Type - Integer
The transformation type parameter, TRT, qualifies the mapping transformation specified by the MAP parameters, as follows:

- Value
Effect

- -1
Direction, magnitude, and location are all transformed. This option is not currently supported by any of the pre-defined coordinate system mappings.

- 0
Only location is transformed

- 1 (default)
Direction and location are transformed

This parameter allows you to distinguish between a system that provides a mapping of location only into an essentially cartesian space, and one in which the space itself mapped. To understand the difference, using polar coordinates as an example, imagine a set of wind speed monitoring units located on a radial grid around some central point such as an airport control tower. Each unit´s position is defined in terms of its distance from the tower and its angular direction from due east. However, the data collected by each monitoring unit is represented as conventional eastward and northward wind components. Assuming the towers´s location is at a moderate latitude, and the monitoring units are reasonably ´local´, this is an example of mapping a radially defined location into a nearly cartesian space (i.e. if the northward components were all set to 0.0, the streamlines defined by the eastward components would all be parallel straight lines. One would set MAP to two (for the polar transformation) and TRT to zero to model this data on a plot generated by the Streamlines utility.

On the other hand, picture a set of wind data, again given as eastward and northward wind components, but this time the center of the polar map is actually one of the earth´s poles. In this case, the eastward components do not point in a single direction; instead they outline a series of concentric circles around the pole. This is a space mapping transformation: one would again set MAP to two, but TRT would be set to one to transform both direction and location.

Changing the setting of this parameter affects the end results only when a non-uniform non-linear mapping occurs at some point in the transformation pipeline. For this discussion a uniform linear transformation is defined as one which satisfies the following equations:

x_out = x_offset + scale_constant * x_in

y_out = y_offset + scale_constant * y_inIf scale_constant is not the same for both equations then the mapping is non-uniform.

This option is currently implemented only for the pre-defined MAP parameter codes, 0 and 2, the identity mapping and the polar coordinate mapping. However, it operates on a different stage of the transformation pipeline in each case. The polar mapping is non-linear from data to user coordinates. The identity mapping, even though necessarily linear over the data to user space mapping, can have a non-uniform mapping from user to NDC space, depending on the values given to the input parameters of the SET call. This will be the case whenever the LL input parameter specifies a logarithmic scaling or the viewport and the user coordinate boundaries do not have the same aspect ratio. Thus for a MAP value of 2, TRT affects the mapping between data and user space, whereas for MAP set to 0, TRT influences the mapping between user and NDC space.

- USV - U Array Special Value - Real
USV is the U vector component array special value. It is a value outside the range of the normal data used to indicate that there is no valid data for this grid location. When the special value flag parameter, SVF, is non-zero, each time a streamline enters a new cell Streamlines will check for this special value in the U array at each of the four corners of the grid box. Anytime the special value is discovered, the current streamline is terminated and a new one started if possible. The default value given to USV is 1.0 * 10**12.

- VNL - Vector Normalization Value - Real
The parameter, VNL, determines the value Streamlines uses to normalize the vector flow field, before beginning the streamline construction loop. When Streamlines is used with the pre-Version 3.2 mapping routines, FX and FY, the value of VNL determines the step size in the grid coordinate system used to construct the streamlines, as a fraction of the grid box size. When using FX and FY, smaller values of VNL result in smaller steps, more processing time and, within the limits of the processor´s floating point accuracy, a higher precision plot. However, if the mapping has non-linearities, the grid size does not remain constant over the transformation and the step size can vary greatly, resulting in discontinuities in certain areas of the plot.

Streamline´s new mapping routines define the streamline differential magnitude in NDC space, ensuring a constant step size over the whole plot, notwithstanding any non-linearity in the transformation. When using the new mapping routines, the parameter DFM controls the step size in NDC space, and VNL is not adjustable by the user. (See the discussion of the compatibility mode parameter, CPM, for a discussion of how to switch between the old and new mapping routines.) The default value of VNL is 0.33.

- VPB - Viewport Bottom - Real
The parameter VPB has an effect only when SET is non-zero, specifying that Streamlines should do the call to SET. It defines a minimum boundary value for the bottom edge of the viewport in NDC space, and is constrained to a value between 0.0 and 1.0. It must be less than the value of the Viewport Top parameter, VPT. The actual value of the viewport bottom edge used in the plot may be greater than the value of VPB, depending on the setting of the Viewport Shape parameter, VPS. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of VPB is 0.05.

- VPL - Viewport Left - Real
The parameter VPL has an effect only when SET is non-zero, specifying that Streamlines should do the call to SET. It defines a minimum boundary value for the left edge of the viewport in NDC space, and is constrained to a value between 0.0 and 1.0. It must be less than the value of the Viewport Right parameter, VPR. The actual value of the viewport left edge used in the plot may be greater than the value of VPL, depending on the setting of the Viewport Shape parameter, VPS. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of VPL is 0.05.

- VPR - Viewport Right - Real
The parameter VPR has an effect only when SET is non-zero, specifying that Streamlines should do the call to SET. It defines a maximum boundary value for the right edge of the viewport in NDC space, and is constrained to a value between 0.0 and 1.0. It must be greater than the value of the Viewport Left parameter, VPL. The actual value of the viewport right edge used in the plot may be less than the value of VPR, depending on the setting of the Viewport Shape parameter, VPS. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of VPR is 0.95.

- VPS - Viewport Shape - Real
The parameter VPS has an effect only when SET is non-zero, specifying that Streamlines should do the call to SET; it defines the desired viewport shape, as follows:

- Value
Effect

- <0.0
The absolute value of VPS specifies the shape to use for the viewport, as the ratio of the viewport width to its height,

- 0.0
The viewport completely fills the area defined by the boundaries specifiers, VPL, VPR, VPB, VPT

- >0.0,<1.0 (0.25,default)
Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape if MIN(R, 1.0/R) is greater than VPS. Otherwise determine the shape as when VPS is equal to 0.0.

- >= 1.0
Use R = (XCM-XC1)/(YCN-YC1) as the viewport shape if MAX(R, 1.0/R) is less than VPS. Otherwise make the viewport a square.

The viewport, whatever its final shape, is centered in, and made as large as possible in, the area specified by the parameters VPB, VPL, VPR, and VPT. You must initialize Streamlines with a call to STINIT after modifying this parameter.

- VPT - Viewport Top - Real
The parameter VPT has an effect only when SET is non-zero, specifying that Streamlines should do the call to SET. It defines a maximum boundary value for the top edge of the viewport in NDC space, and is constrained to a value between 0.0 and 1.0. It must be greater than the value of the Viewport Bottom parameter, VPB. The actual value of the viewport top edge used in the plot may be less than the value of VPT, depending on the setting of the Viewport Shape parameter, VPS. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of VPT is 0.95.

- VSV - V Array Special Value - Real
VSV is the V vector component array special value. It is a value outside the range of the normal data used to indicate that there is no valid data for this grid location. When the special value flag parameter, SVF, is non-zero, each time a streamline enters a new cell Streamlines will check for this special value in the V array at each of the four corners of the grid box. Anytime the special value is discovered, the current streamline is terminated and a new one started if possible. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value given to VSV is 1.0 * 10**12.

- WDB - Window Bottom - Real
When STINIT does the call to SET, the parameter WDB is used to determine argument number 7, the user Y coordinate at the bottom of the window. If WDB is not equal to WDT, WDB is used. If WDB is equal to WDT, but YC1 is not equal to YCN, then YC1 is used. Otherwise, the value 1.0 is used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of WDB is 0.0.

- WDL - Window Left - Real
When STINIT the call to SET, the parameter WDL is used to determine argument number 5, the user X coordinate at the left edge of the window. If WDL is not equal to WDR, WDL is used. If WDL is equal to WDR, but XC1 is not equal to XCM, then XC1 is used. Otherwise, the value 1.0 is used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of WDL is 0.0.

- WDR - Window Right - Real
When STINIT does the call to SET, the parameter WDR is used to determine argument number 6, the user X coordinate at the right edge of the window. If WDR is not equal to WDL, WDR is used. If WDR is equal to WDL, but XCM is not equal to XC1, then XCM is used. Otherwise, the value of the STINIT input parameter, M, converted to a real, is used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of WDR is 0.0.

- WDT - Window Top - Real
When STINIT does the call to SET, the parameter WDB is used to determine argument number 8, the user Y coordinate at the top of the window. If WDT is not equal to WDB, WDT is used. If WDT is equal to WDB, but YCN is not equal to YC1 then YCN is used. Otherwise, the value of the STINIT input parameter, N, converted to a real, is used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of WDT is 0.0.

- XC1 - X Coordinate at Index 1 - Real
The parameter XC1 specifies the X coordinate value that corresponds to a value of 1 for the first subscript of the U and V, vector field component arrays. Together with XCM, YC1, and YCN it establishes the mapping from grid coordinate space to data coordinate space. If XC1 is equal to XCM, 1.0 will be used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of XC1 is 0.0.

- XCM - X Coordinate at Index M - Real
The parameter XCM specifies the X coordinate value that corresponds to the value of the STINIT input parameter, M, for the first subscript of the U and V vector component arrays. Together with XC1, YC1, and YCN it establishes the mapping from grid coordinate space to data coordinate space. If XC1 is equal to XCM, the value of M, converted to a real, will be used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of XCM is 0.0

- YC1 - Y Coordinate at Index 1 - Real
The parameter YC1 specifies the Y coordinate value that corresponds to a value of 1 for the first subscript of the U, V, vector component arrays as well as for the P scalar data array, if used. Together with YCN, XC1, and XCM it establishes the mapping from grid coordinate space to data coordinate space. If YC1 is equal to YCN, 1.0 will be used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of YC1 is 0.0

- YCN - Y Coordinate at Index N - Real
The parameter YCN specifies the Y coordinate value that corresponds to the value of the STINIT input parameter, N, for the second subscript of the U and V vector component arrays as well as the P scalar data array, if used. Together with YC1, XC1, and XCM it establishes the mapping from grid coordinate space to data coordinate space. If YC1 is equal to YCN, the value of N, converted to a real, will be used. You must initialize Streamlines with a call to STINIT after modifying this parameter. The default value of YCN is 0.0

- ZFC - Zero Field Text Block Color - Integer
If ZFC is greater or equal to zero, it specifies the GKS color index to use to color the Zero Field text block. Otherwise the Zero Field text block is colored using the current GKS text color index. The default value of ZFC is -1.

- ZFP - Zero Field Text Block Positioning Mode - Integer
The ZFP parameter allows you to justify, using any of the 9 standard justification modes, the Zero Field text block unit with respect to the position established by the parameters, ZFX and ZFY The position modes are supported as follows:

- Mode
Justification

- -4
The lower left corner of the text block is positioned at ZFX, ZFY.

- -3
The center of the bottom edge is positioned at ZFX, ZFY.

- -2
The lower right corner is positioned at ZFX, ZFY.

- -1
The center of the left edge is positioned at ZFX, ZFY.

- 0 (default)
The text block is centered along both axes at ZFX, ZFY.

- 1
The center of the right edge is positioned at ZFX, ZFY.

- 2
The top left corner is positioned at ZFX, ZFY.

- 3
The center of the top edge is positioned at ZFX, ZFY.

- 4
The top right corner is positioned at ZFX, ZFY.

- ZFS - Zero Field Text Block Character Size - Real
ZFS specifies the size of the characters used in the Zero Field graphics text block as a fraction of the viewport width. The default value is 0.033.

- ZFT - Zero Field Text String - Character* 36
Use ZFT to modify the text of the Zero Field text block. The Zero Field text block may appear whenever the U and V vector component arrays contain data such that all the grid points otherwise eligible for plotting contain zero magnitude vectors. Currently the string length is limited to 36 characters. Set ZFT to a single space (´ ´) to prevent the text from being displayed. The default value for the text is ´Zero Field´.

- ZFX - Zero Field Text Block X Coordinate - Real
ZFX establishes the X coordinate of the Zero Field graphics text block as a fraction of the viewport width. Values less than 0.0 or greater than 1.0 are permissible and respectively represent regions to the left or right of the viewport. The actual position of the block relative to ZFX depends on the value assigned to the Zero Field Positioning Mode parameter, ZFP. The default value is 0.5.

- ZFY - Zero Field Text Block Y Coordinate - Real
ZFY establishes the Y coordinate of the minimum vector graphics text block as a fraction of the viewport height. Values less than 0.0 or greater than 1.0 are permissible and respectively represent regions below and above the viewport. The actual position of the block relative to ZFY depends on the value assigned to the Zero Field Positioning Mode parameter, ZFP. The default value is 0.5.

## See Also

Online: stgetc, stgeti, stgetr, stinit, stream, streamlines, strset, stsetc, stseti, stsetr, stuixy, stumsl, stumta, stumxy, ncarg_cbind.

Hardcopy: NCAR Graphics Fundamentals, UNIX Version

## Copyright

Copyright (C) 1987-2009

University Corporation for Atmospheric Research

The use of this Software is governed by a License Agreement.