Function:     irds_rd_skypos

Purpose:      To read skypositions for satcal ticks from an IRDS

Category:     IR

File:         irds_samples.c

Author:       P.R. Roelfsema

Use:          IRDS_RD_SKYPOS(  IRDS   ,    Input   character*(*)
                               SNIP   ,    Input   integer
                               TICK   ,    Input   integer
                               LON    ,    Output  double( >=NSATS )
                               LAT    ,    Output  double( >=NSATS )
                               TWIST  ,    Output  double( >=NSATS )
                               NSATS  ,    Input   integer
                               STATUS )    Output  integer
                                       
              IRDS        Name of IRDS to read from.
              SNIP        Sequential snip number to read.
              TICK        Sequential tick of first sample to read.
              LON         Array to receive LON coordinates
              LAT         Array to receive LAT coordinates
              TWIST       Array to receive TWIST angles (ccw w.r.t. +LAT)
              NSATS       Number of satcal ticks  to read.
              STATUS      Error return code:
                           0  - no error.
                          -1  - IRDS does not exist
                          -2  - IRDS is not a legal irds
                          -3  - SNIP not in IRDS
                          -5  - TICK or TICK + NSATS not in IRDS
                          -7  - no coordinate info in header

Updates:      Aug 20, 1990: PRR, Creation date