Development of a three-dimensional least squares adjustment program
Gerald W Johnson
Report no. Mn/DOT 1995-09
Topics: Traffic Modeling and Data
In the past horizontal position (X and Y coordinates) and vertical position (elevation) have been measured and computed in separate surveying operations. In order to take full advantage of the three-dimensional measurement capability of their "total station" surveying instruments, Mn/DOT wanted a user friendly least squares adjustment program that would simultaneously incorporate all three measurements - distance, horizontal angle and vertical angle in a common adjustment procedure. The only practical way to do this is to use a least squares adjustment program that can determine both horizontal and vertical components in the same adjustment procedure. There are commercial and government adjustment programs available that will do a three dimensional least squares adjustment, and the new program is not unique in that sense. It is unique, however, in that it satisfies special Mn/DOT requirements, particularly with respect to input and output format which is the SDMS (Survey Data Management System) format. In addition the program incorporates a simplified weighting procedure which allows the user to alter the weighting parameters if that should be necessary.
Although not a part of the original agreement, it became apparent during program testing that a field test facility would benefit the project and also provide a site for on-going equipment testing and performance checking. Thus the idea for a permanent three-dimension test site came into being.