## COV: Covariance Matrix Header

The COV record is used in coordinate and coordinate difference observation groups (2DC, 2DD, 3DC, and 3DD) for specifying that covariance matrix data follows.

The UPPR matrix form specifies that upper-triangular elements are input, and the DIAG form specifies that only diagonal elements are input.

The coordinate system types are:

Note that the addition constants and factors are applied to the covariance matrix. All additive values (for entire matrix, for diagonal elements, and PPM) are applied to the matrix first, then the factors are applied. Addition constants are added directly to the covariance matrix (no squaring takes place). The PPM value is used to compute a standard deviation which is then squared before adding it to the diagonal elements of the covariance matrix.

**The format of the COV record is as follows:****Columns 002-005**: COV**Columns 007-008**: Coordinate system of matrix (LG or CT)**Columns 010-013**: Matrix form (UPPR or DIAG, see below)**Columns 015-024**: Addition constant for entire matrix**Columns 026-035**: Scale factor for entire matrix**Columns 037-046**: Addition constant for diagonal elements**Columns 048-057**: Scale for diagonal elements**Columns 059-068**: PPM for diagonal elements**Columns 070-079**: Addition constant for height/Z**Columns 081-090**: Scale for height/Z**Columns 092-093**: Linear unit nameThe UPPR matrix form specifies that upper-triangular elements are input, and the DIAG form specifies that only diagonal elements are input.

The coordinate system types are:

**LG**: Local geodetic (North, East, Up)**CT**: Conventional Terrestrial (Geocentric X, Y, Z)Note that the addition constants and factors are applied to the covariance matrix. All additive values (for entire matrix, for diagonal elements, and PPM) are applied to the matrix first, then the factors are applied. Addition constants are added directly to the covariance matrix (no squaring takes place). The PPM value is used to compute a standard deviation which is then squared before adding it to the diagonal elements of the covariance matrix.