Geoida Help

Least squares adjustment is 'Rank Deficient'

Question: While processing a least squares adjustment a message appears to say that the network is “rank-deficient”.

Answer: A 'rank-deficient' network is one in which there are fewer than the necessary constraints present to adequately define the network 'datum', i.e., the position, orientation and scale. For example, a 1D vertical network requires at least one height to be held fixed for position and scale to be applied by either the height-difference observations or a second fixed height, while a 2D network requires at least one fixed coordinate pair (easting and northing) for position, an azimuth for orientation and a distance for scale, or two fixed coordinate pairs for position, orientation and scale. Since Geoida requires ordinary minimum constraints to adjust the network, any shortfalls in the parameters above will result in a 'rank-deficient' network.

Ensure that sufficient control points or individual coordinate values are set 'Fixed' and that observations of the correct type are present or also set 'Fixed'.