Function:      GDS___UNPACK

Purpose:       unpack a grid value from a coordinate word

Category:      GDS

File:          gds___unpack.c

Author:        W. Zwitser

Use:           INTEGER GDS___UNPACK( SET,             Input        character 
                                     COORD_WORD,      Input        integer
                                     IAX,             Input        integer
                                     ERR )            In/Out       integer

               GDS___UNPACK   grid value

               SET            name of set

               COORD_WORD     coordinate word from which grid is unpacked

               IAX            axis number of grid value 
                              ( 0 ... N-1 with N axes ) 

               ERR            error return code :
                              =  0 : successful
                               -11 : iax < 0 or iax >= number of set axes
                               -19 : axis undefined in coordinate word

Updates:       Dec  5, 1989: WZ,  migrated to C
               Oct 31, 1990: WZ, 'naxis', etc. from setsta -> dsc_file
               Mar 23, 1994: JPT, modified to cooperate with GDS server
               Apr 09, 2009: VOG, Changed definition of NINT to force correct
                                  processing of coordinates when CRPIX ends
                                  on .5 in all functions dealing with coordinates.