General Layout of Observation Groups

All observation groups in GeoLab should begin with a GRP record, which effectively names the group of measurements (the next paragraph describes how names should be constructed). The group name has no effect on the network adjustment, but it simplifies the revisions to your IOB file when residuals are flagged in the output listing. The observations named by a GRP record are all of those measurements following that GRP record, up to the next GRP record encountered.

The name specified in a GRP record can be used to easily locate measurements in an IOB file that correspond to residuals listed in the output listing (*.LST) file. When residuals are listed, the GRP "name" (the text in a GRP record) is also output with those residuals. If the GRP record name contains: 1 - an indication of which IOB file the measurements are in (e.g. a file name, or a project name); and 2 - a sequence or other number that indicates where in the file to find the measurements in the group, then it is easy to find the measurements.

The general structure of observation groups is as follows (please note that we will use square brackets, [], to enclose a description of a group of one or more records):
GRP Observation Group 001
[Observations in Group 001]
GRP Observation Group 002
[Observations in Group 002]
etc...

The general layout of records for the 2DC, 2DD, 3DC, and 3DD observation groups is as follows:
[Header record (2DC, 2DD, 3DC, or 3DD)]
[Set of measurement value records]
[Covariance matrix header record]
[Matrix elements records]

The "Covariance matrix header record" and the "Matrix elements records" are formatted the same for all types of header records (2DC, 2DD, 3DC, and 3DD).