## 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.

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 this record is as follows (from column - to column: description):**- 002-005: COV
- 007-008: Coordinate system of matrix (LG or CT)
- 010-013: Matrix form (UPPR or DIAG, see below)
- 015-024: Addition constant for entire matrix
- 026-035: Scale factor for entire matrix
- 037-046: Addition constant for diagonal elements
- 048-057: Scale for diagonal elements
- 059-068: PPM for diagonal elements
- 070-079: Addition constant for height/Z
- 081-090: Scale for height/Z
- 092-093: Linear unit name

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:**- 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.