Ubuntu Manpage: STUMXY - Maps a single point on the streamline from data to user coordinate space.

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.

COPYRIGHT