Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
map_set, contour, path_filename norm to lon,lat coord
After using MAP_SET and then CONTOUR to draw contour lines on a map projection, I am trying to find a reasonable way to obtain lists of longitude and latitude coordinates along the contours that were drawn. Calling CONTOUR a second time with the PATH_FILENAME options gives normalized coordinates along all contour lines. (The PATH_INFO and PATH_XY options to CONTOUR do not seem to work well, because they apparently only return info about closed contours. Using the /CLOSED option to CONTOUR makes things worse with stray contour lines crossing the center of the plot from the extreme boundaries.) ) So the less efficient PATH_FILENAME option to CONTOUR generates an unformatted file with all the normal coodinates, and I can then input this info. But how do I then convert these lists of normalized coordinates to longitude and latitude for the projection as specified in the most recent call to MAP_SET? The CONVERT_COORD routine does not seem to do the job, as a request to convert from normalized TO_DATA results in normalized coordinates. There are hints in various idl documentation that the !MAP system variable may be involved, but I have been unable to locate any details about how to use !MAP to convert normal coord back to lon lat in a general way for any projection. Does a NORMAL_TO_LON_LAT routine exist for use after a call to MAP_SET? I'm hoping to use this with !P.MULTI for multiple maps on each frame, so I am guessing it needs to handle normalized coordinates relative to the entire frame, and not relative to the frame subset for each map. Thanks Bill McKie Sterling Software NASA Ames Research Center mckie@sky.arc.nasa.gov