- (REAL, input): The X coordinate of a point on the streamline in data coordinate space.
- (REAL, input): The Y coordinate of a point on the streamline in data coordinate space.
- (REAL, output): The X coordinate of the point in user coordinate space.
- (REAL, output): The Y coordinate of the point in user coordinate space.
- (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.
USAGESTUMXY 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.
ACCESSTo use STUMXY, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.
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University Corporation for Atmospheric Research
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