stumxy(3NCARG)
NAME
STUMXY - Maps a single point on the streamline from data to user coordinate space.
SYNOPSIS
CALL STUMXY(XDA,YDA,XUS,YUS,IST)
DESCRIPTION
XDA (REAL, input): The X coordinate of a point on the
streamline in data coordinate space.
YDA (REAL, input): The Y coordinate of a point on the
streamline in data coordinate space.
XUS (REAL, output): The X coordinate of the point in user
coordinate space.
YUS (REAL, output): The Y coordinate of the point in user
coordinate space.
IST (REAL, output) Status of the mapping operation: 0 indicates
success, negative values indicate that the mapping failed;
positive values are reserved and should not be used by the
implementor of a mapping routine.
USAGE
STUMXY is a user-modifiable routine provided to support custom mappings
of the data coordinate space. The user does not invoke it directly.
Instead, whenever the parameter MAP specifies a mapping not handled by
Streamlines internally (i.e., when MAP is set to a value other than 0,
1, or 2), Streamlines calls STUMXY as needed during the process of
creating a streamline. The default version of STUMXY simply performs an
identity mapping. In order to implement a custom mapping, you must pick
a unique mapping code (a positive integer greater than 2), and then
modify each of the three routines, STUMXY, STUIXY, and STUMTA to
recognize and respond consistently to the chosen code. In the standard
distribution of NCAR Graphics, these three routines reside in a single
file, stumxy.f. STUMXY maps a point from data to user coordinate
space, STUIXY inversely maps a point from user to data coordinate
space, and STUMTA, which is likely to be the most difficult to
implement, finds the tangent angle of the streamline at a point in NDC
space.
STUMXY has access to a common block called STMAP that contains a number
of variables used to record the current transformation state. In order
to accommodate a variety of mapping implementations, STMAP provides
more information than normally required. Consider the values stored in
STMAP as strictly read-only. One essential member of this common block
is IMAP, which contains the value currently assigned to the MAP
parameter.
In STUMXY, the implementor of a custom mapping needs to add code of the
form:
IF (IMAP .EQ. <chosen_map_code>) THEN
...map XDA to XUS
...map YDA to YUS
...if error, set IST to a negative value
RETURN
ENDIF
Note that after the return from STUMXY, Streamlines checks to ensure
that XUS and YUS are within the current boundaries of the user
coordinate system.
When implementing a custom mapping, you may wish to look at the coding
of the pre-defined mappings (0, identity mapping; 1, Ezmap projections;
and 2, polar coordinate mapping) in the file stmpxy.f. For these
mappings, the subroutine STMPXY is the equivalent of STUMXY; it has an
identical interface and may serve as a model for your implementation.
ACCESS
To use STUMXY, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.
SEE ALSO
Online: stgetc, stgeti, stgetr, stinit, stream, streamlines, streamlines_params, 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.
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