= Known processing problems =

== CASI data missing GPS sync ==

If you're seeing azgcorr failing with `** read error on SCO input` and, earlier in the output, azcaschk2 is reporting:
{{{
GPS message time to CASI clock time difference(s)...
  del_t : 
  freq  : 
  most frequent gap is: 0  secs

** NO (or insufficient) GPS messages or sync pulses
**    ... no sync saved
}}}

This means the CASI data files are missing the GPS sync markers (or azcaschk2 can't find them).  As a consequence, scans can't be tied to navigation and azgcorr has nothing to work with.  Typically, you'll be able to get the file to level 1 without problems, but level 3 can't be done.

To work around the lack of GPS sync, azcaschk2 allows you to use "frame headers" for sync instead.  You need to add `-FRsync` to the azcaschk2 command line.  In the normal batch files, amend the CSYNC line to read: `CSYNC="-FRsync"`.

This should then process through to level 3, though you may need to correct for navigation timing.