From the Carlson SurvNet Help:

The following is a typical vector record in the StarNet ASCII format. GPS vectors typically consist of the 'from' and 'to' point number, the delta X, delta Y, delta Z values from the 'from' and 'to' point, with the XYZ deltas being in the geocentric coordinate system. Additionally the variance/covariance values of the delta XYZ's are included in the vector file.

.GPS WEIGHT COVARIANCE

C PRS34452 1305780.345005 -4667085.299019 4132689.544939 0.005000 0.005000 0.005000 --MON

C UCNJ 1305780.345005 -4667085.299019 4132689.544939 0.00000100 0.00000100 0.00000100 --MON

G1 UCNJ-1000 8399.71318061 -4742.15645068 -8036.07224424 --MNS

G2 3.939428e-006 2.474560e-005 1.160301e-005

G3 3.924536e-006 -3.360765e-006 -1.028503e-006

G1 UCNJ-1001 8328.15569476 -4796.59445569 -8072.25948922 --MNS

G2 9.596618e-007 1.687749e-005 1.936038e-006

G3 1.176891e-007 -8.668020e-009 -4.798408e-006

The first line defines what values are in the G2 and G3 records. It can be either GPS WEIGHT COVARIANCE (G2 is Variance, G3 is Covariance), or GPS WEIGHT STDERRCORRELATION (G2 is standard error, G3 is standard error correlation). This line is optional; the default is COVARIANCE.

The next two lines are coordinate control records. These records are also optional. If used, they must be Geocentric Coordinates (XYZ) in metric units. The format is as follows:

C PointName X Y Z StdErrX StdErrY StdErrZ --PointDescription

The standard errors and point description are optional.

The GO record is a comment.

The G1 record includes the 'from' and 'to' points and the delta X, delta Y, and delta Z in the geocentric coordinate system and an optional description of the rover point.

The G2 record is the variance (or standard error) of X,Y, and Z. The G3 record contains the covariance (or standard error correlation) of XY, ZX, and ZY. Most all GPS vector files contain the same data fields in different formats.