Computer Program GALS

Abstract

GALS, an acronym for Geographic Adjustment by Least Squares, is a comprehensive electronic computer program for adjusting horizontal control survey networks of triangulation, trilateration, traverse or any combination thereof. Adjustment is by variation of geographic coordinates using observation equations. Input includes coordinates, fixed or preliminary, for all points, and observed lengths, azimuths, and directions appropriately weighted; it may also include correlated position equations thus enabling the user to carry out adjustment by sections. Output includes adjusted coordinates for all points, residuals for all observations, and covariance factors for points selected by the user. Standard error ellipse data for a point or points relative to datum (fixed points) or to any other point may be printed out on request. The program can be used for network design as well as for adjustment; with the program in simulation mode a proposed survey network can be entered and standard error ellipses to analyze the configuration can be called for. As the program is in basic Fortran IV it is relatively machine independent. Space requirements in computer core storage is reduced by banding the matrix of normal coefficients into a diagonal band, a vertical band and a unit matrix band.