PROJ

PROJ is the coordinate transformation software underneath most free GIS programs. It converts coordinates between reference systems, including datum transformations, and supports more than a hundred map projections. Alongside the library come command-line tools: cs2cs to convert between any two coordinate systems, cct for 4D transformations, projinfo to query definitions and transformation pipelines, geod for geodesic distance calculations and projsync to download correction grid files. Suited to surveyors and engineers who need to convert point files accurately or check which transformation is being applied. Limitations: there is no graphical interface, and the project distributes source code only – ready-made binaries come through OSGeo4W, conda, Homebrew or Linux package managers.