SALSA: An Open Source Geodetic Least Squares Adjustment Software Suite

Applied Research Laboratories, The University of Texas at Austin (ARL:UT) has developed the Surveyor's Applications for Least Squares Adjustment (SALSA), a geodetic least squares adjustment application suite which optimally combines dissimilar spatial measurements to minimize a survey network's measurement residuals and yield optimal estimates of surveyed point locations.

SALSA is a rigorous 3-D weighted least squares suite built in C++ and leverages several well-established open source libraries, including ARL:UT's GPS Toolkit for geodetic transforms, the Eigen linear algebra library for high performance matrix equation solutions, the Marble library for interactive mapping, and others. The SALSA user interface is built on the Qt application framework and currently supports Microsoft Windows and Linux platforms.

SALSA accepts all common geodetic survey measurement types, including distances, horizontal and vertical angles, direction sets, height differences, and GNSS-derived measurements including 3-D vectors and absolute position estimates. The least squares observation equation system is formulated in an earth-centered, earth-fixed Cartesian reference frame for rigorous 3-D adjustment. Adjustments account for geoid undulations using global or user-specified geoid models.

The National Geospatial-Intelligence Agency (NGA), which has funded ARL:UT's development of SALSA, fulfills a broad range of extraordinary geodetic survey requirements for the U.S. Department of Defense and other entities. Thus, NGA demands a high degree of performance from the SALSA application suite and values transparency of the software source code to support inspection of underlying algorithms and implementation. ARL:UT and NGA are making SALSA available as free and open source software under the GNU General Public License (GPLv3) as a benefit to the geodetic survey community.

Approved for Public Release #19-875