velvct(3NCARG)
NAME
VELVCT - Plots a vector field, given two 2-dimensional vector component arrays, U and V. You may control certain characteristics of the plot by adjusting the values given to the input arguments. Other less frequently changed characteristics may be affected by modifying VELDAT, the BLOCK DATA routine that initializes members of the common blocks VEC1 and VEC2. In addition, depending on the value given to the compatibility parameter, CPM, you may set other options by calling VVSETC, VVSETI, or VVSETR to modify internal parameters.
SYNOPSIS
CALL VELVCT (U,LU,V,LV,M,N,FLO,HI,NSET,LENGTH,ISPV,SPV)
STATUS
VELVCT is obsolete, and is supported only to provide compatibility with old NCAR Graphics codes. However, the compatibility mode parameter, CPM, offers a number of options to help ease the the transition to the new version of the utility. When writing new code you are encouraged not to use this entry point, since it provides less capability than the standard Vectors interface, and may eventually be phased out.
C-BINDING SYNOPSIS
#include <ncarg/ncargC.h>
void c_velvct(float *u, int lu, float *v, int lv, int m,
int n, float flo, float hi, int nset,
int length, int ispv, float *spv)
DESCRIPTION
U (REAL 2-dimensional array, dimensioned LU x n: n >= N,
input): By default, assumed to contain the first
dimensional Cartesian components of the vector field.
However, if PLR is non-zero, it is treated as containing
the vector magnitudes.
LU (INTEGER, input): Actual value of the first dimension of
array U.
V (REAL 2-dimensional array, dimensioned LV x n: n >= N,
input): By default, assumed to contain the second
dimensional Cartesian components of the vector field.
However, if PLR is non-zero, it is treated as containing
the vector angles.
LV LV (INTEGER, input): Actual value of the first dimension of
array V.
M (INTEGER, input): Number of contiguous elements along the
first dimensional axis containing data to be processed in
each of the arrays, U and V.
N (INTEGER, input): Number of contiguous elements along the
second dimensional axis containing data to be processed in
each of the arrays, U and V.
FLO (REAL, input): Minimum vector magnitude allowed to be
displayed in the plot.
HI (REAL, input): Maximum vector magnitude allowed to be
displayed in the plot. If set to 0.0 there is no upper
limit imposed.
NSET (INTEGER, input): Flag that controls how and when the SET
call is invoked. If NSET is 0, VELVCT makes a SET call to
establish a standard viewport and window boundaries
coincident with the array coordinate boundaries. PERIM is
called to draw a border. If NSET is greater than zero,
VELVCT does not call SET or PERIM. If NSET is less than
zero, VELVCT calls SET to establish window boundaries
coincident with the array grid coordinate boundaries but
does not modify the viewport or call PERIM. Unlike the
VVINIT/VVECTR interface, when VELVCT does a SET call, it
always restores the original coordinate system state before
returning.
LENGTH (INTEGER, input): The length in plotter address units
(PAUs) used to render the vector with the greatest
magnitude that is eligible for plotting. A vector is
eligible for plotting if it is less than or equal to the
value of HI, unless HI is 0.0 in which case all vectors are
eligible. If LENGTH is set to 0.0, the length selected is
one half the diagonal length of a grid cell assuming a
linear mapping of the grid coordinate space into the
viewport.
ISPV (INTEGER, input): Flag to control the special value
feature. 0 means that the feature is not in use. 1 means
that if the value of U(I,J)=SPV(1) the vector will not be
plotted. 2 means that if the value of V(I,J)=SPV(2) the
vector will not be plotted. 3 means that if either
U(I,J)=SPV(1) or V(I,J)=SPV(2) then the vector will not be
plotted. 4 means that if U(I,J)=SPV(1) and V(I,J)=SPV(2),
the vector will not be plotted.
SPV (REAL array, dimensioned 2, input): An array of length 2
which gives the value in the U array and the value in the V
array which denote special values. This argument is ignored
if ISPV=0. The default values are 1.0E12.
C-BINDING DESCRIPTION
The C-binding argument descriptions are the same as the FORTRAN
argument descriptions with the following exceptions:
lu The second dimension of u in the calling program.
lv The second dimension of v in the calling program.
m Number of contiguous elements along the second dimensional
axis containing data to be processed in each of the arrays,
u and v.
n Number of contiguous elements along the first dimensional
axis containing data to be processed in each of the arrays,
u and v.
USAGE
Beginning with version 3.2 of NCAR Graphics, the VELVCT entry point has
been recoded as a front end to the VVINIT/VVECTR interface to Vectors.
The compatibility mode parameter, CPM, controls the degree to which a
call to the Version 3.2 VELVCT emulates the older call. Appropriate
settings of CPM can separately address each of the following three
questions regarding the level of emulation:
* Should FX, FY, MXF, and MYF rather than the Version 3.2 mapping
routines perform the mapping to user coordinates?
* Should the input arguments FLO, HI, NSET, LENGTH, ISPV, SPV
override the current values of the corresponding Vectors'
internal parameters?
* Should the values contained in the common blocks VEC1 and VEC2
override the current values of corresponding Vectors' internal
parameters?
Given the default value of CPM, all these questions are answered in the
affirmative, and a call to VELVCT gives a reasonably faithful emulation
of the older version's behavior.
However, even in this case, it is possible to use the parameter setting
routines to control the behavior of features that have no counterpart
in the older version of VELVCT, as long as the feature is accessible
without calling the new interface. For instance, you could control the
vector linewidth by setting the LWD parameter, although you could not
draw vectors masked to an area map because doing so requires direct
invocation of VVECTR
The following two tables show how the VELVCT input arguments and
VEC1/VEC2 common block members map into internal parameters currently
supported by Vectors. (Consult the vectors_params man page for
descriptions of the internal parameters.)
Input Argument Internal Parameter
FLO VLC (VLC is set to -FLO if FLO is
positive, 0.0 otherwise)
HI VHC (VHC is set to -HI if HI is positive,
0.0 otherwise)
NSET SET (NSET = 0 is approximately equivalent
to SET = 1)
LENGTH VRL (LENGTH in Plotter Address Units is
converted to VRL as a fraction of the
viewport width)
ISPV SVF
SPV(1) USV
SPV(2) VSV
Common Block Member Internal Parameter
EXT VPS
ICTRFG VPO
ILAB LBL
IOFFD DPF
RMN AMN (RMN in metacode coordinates is
converted to AMN as a fraction of the
viewport width)
RMX AMX (RMX in metacode coordinates is
converted to AMX as a fraction of the
viewport width)
SIZE LBS (Character size in metacode
coordinates is converted to LBS as a
fraction of viewport width)
INCX XIN
INCY YIN
- MNT (When common blocks VEC1 and VEC2
override parameter settings, MNT is always
set to " ", indicating that the minimum
vector text block is not to be displayed.)
IOFFM MXT (If IOFFM is non-zero, MXT is set to "
", indicating that the maximum text block
is not to be displayed. Otherwise MXT is
set to the string "MAXIMUM VECTOR")
IOFFM MXX (If IOFFM is 0, MXX is set to a
computed value that, as a fraction of the
viewport width, specifies a point 0.05 in
NDC left of the right hand edge of the
plotter frame.)
IOFFM MXY (If IOFFM is 0, MXY is set to a
computed value that, as a fraction of the
viewport height, specifies a point 0.005
in NDC up from the bottom edge of the
plotter frame.)
IOFFM MXP (If IOFFM is 0, MXP is set to -2,
indicating that the text block should be
lower-right justified.
Note that the emulation of the maximum vector text block differs from
the older implementation in that it now uses high-quality text.
EXAMPLES
Use the ncargex command to see the following relevant example: stex02, tvelvc.
ACCESS
To use VELVCT or c_velvct, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.
SEE ALSO
Online: vectors, vectors_params, fx, vvectr, vvgetc, vvgeti, vvgetr, vvinit, vvrset, vvsetc, vvseti, vvsetr, vvudmv, vvumxy, ncarg_cbind.
COPYRIGHT
Copyright (C) 1987-2009 University Corporation for Atmospheric Research The use of this Software is governed by a License Agreement.
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