GT_FILTA uses an index or roadmap structure to determine the setting of the A filter:
IDL> a = gt_filta(index)
The filter setting will be returned as an integer (1-6) where
The last two columns show what GT_FILTA returns when using the /string and /short
options. The routine GET_INFO uses the /string option.
It is possible to get a string type description of the filters used by
typing:
IDL> b = gt_filta(roadmap, /string)
You can get a listing of these at any time by typing the following:
IDL> print,gt_filta()