SYNOPSIS

CALL VVECTR (U,V,P,IAM,VVUDMV,WRK)

C-BINDING SYNOPSIS

#include <ncarg/ncargC.h>

void c_vvectr(float *u, float *v, float *p, int *iam,

              int (*vvudmv_)(float *xcs, float *ycs, 

              int *ncs, int *iai, int *iag, int *nai), 

              float *wrk)

DESCRIPTION

U

(REAL 2 dimensional array, dimensioned as specified in last call to VVINIT, input): By default, assumed to contain the first dimensional axis components of the vector field. However, if PLR is non-zero, it is treated as containing the vector magnitudes.

V

(REAL 2 dimensional array, dimensioned as specified in last call to VVINIT, input): By default, assumed to contain the second dimensional axis components of the vector field. However, if PLR is non-zero, it is treated as containing the vector angles.

P

(REAL 2 dimensional array, dimensioned as specified in last call to VVINIT, input): Array of scalar data that may be used to color the vectors. The grid points are assumed to coincide with the grid points of the U and V arrays. Required only if CTV has an absolute value of 2; otherwise this argument is ignored and may be assigned a dummy value.

IAM

(INTEGER array, unknown dimension, input): Area map array previously established by calls to routines in the Areas utility. It is not examined or modified by Vectors. Required only if MSK is set to a non-zero value; otherwise it is ignored and may be assigned a dummy value.

VVUDMV

(EXTERNAL subroutine, input): User-definable masked drawing subroutine. See the man page vvudmv for a discussion of the usage and argument list required for this subroutine. Required only if MSK is set to a non-zero value; otherwise it is ignored and may be assigned a dummy value.

WRK

(REAL array, dimensioned as specified in last call to VVINIT, input/output): Work array required only if the parameter VMD is set to a value greater than 0.0. Otherwise may be set to a dummy value.

C-BINDING DESCRIPTION

The C-binding argument descriptions are the same as the FORTRAN argument descriptions.

USAGE

A call to VVINIT must precede the first call to VVECTR, and is again required any time the vector or scalar array data changes, any of the coordinate control parameters are modified, or the number of color threshold levels is modified when Vectors is given the responsibility of setting up the color threshold value array. However, the user may modify text elements or any of the rendering control parameters, and if assuming responsibility for setting up the color threshold array, may also modify the color array parameters, in between multiple invocations of VVECTR.

Arguments to VVINIT establish the sizes of the two or three data arrays, as well as the possible work array. VVINIT places these values into common block variables where they become available to VVECTR. Therefore no size arguments need appear in the VVECTR argument list. When there is no scalar data array, area masking is not enabled, and VMD is less than or equal to 0.0, all but the first two arguments to VVECTR may have dummy values and the invocation would be something like:

CALL VVECTR(U,V,IDM,IDM,IDM,IDM)

where IDM is an arbitrary variable, INTEGER or REAL, that need not have been initialized. However, any time the color threshold control parameter, CTV has an absolute value of 2, the auxiliary scalar data array is expected, and the P scalar array variable needs to be specified.

The masking capability supported by Vectors allows the user to overlay vector fields on top of graphics produced by other utilities, such as Conpack contour plots, without encroaching on areas, like label boxes, that should appear in the foreground. Normally the area map should be generated and used in the normal way (as described in the Areas and Conpack documentation) before calling any routines in the Vectors utility. When the parameter MSK has a non-zero value, masking is enabled and a previously created area map must be passed to VVECTR. VVECTR examines the map, returning an error if it determines that it is an invalid map or contains more area maps that it can handle, currently 64. Otherwise its only use of the map is as a member of the argument list when invoking one of the Areas routines, ARDRLN or ARGTAI. The user must also pass in a user-definable masked drawing subroutine. A simple version of this subroutine, named VVUDMV, is supplied with the Vectors utility, and may suffice for basic masked drawing operations. See the vvudmv man page for more information.

The last argument in the calling sequence, WRK, is used only when the parameter VMD (Vector Minimum Distance) is given a value greater than 0.0. In this case, Vectors uses the array to keep track of the location of each vector in NDC space so that the distances between vectors can be compared. Based on these comparisons, Vectors eliminates some vectors such that the remaining vectors are separated by at least the specified distance. Otherwise the WRK argument is ignored, and may be passed a dummy argument value.

EXAMPLES

Use the ncargex command to see the following relevant examples: bnchmk, fcover, ffex00, ffex01, ffex02, ffex05, stex02, stex03, vvex01, vvex02.

ACCESS

To use VVECTR or c_vvectr, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

MESSAGES

See the vectors man page for a description of all Vectors error messages and/or informational messages.

COPYRIGHT

Copyright (C) 1987-2009
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.