CORR: Correlation Matrix Header

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

The format of the CORR record is as follows:

Columns 002-005: CORR
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 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 corresponding covariance matrix (after computing it from the given correlation 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.