GeographicLib is a small set of C++ classes for performing conversions
between geographic, UTM, UPS, MGRS, geocentric, and local cartesian
coordinates, for gravity (e.g., EGM2008), geoid height, and geomagnetic
field (e.g., WMM2020) calculations, and for solving geodesic problems.

It is a suitable replacement for the core functionality provided by geotrans.

WWW: https://geographiclib.sourceforge.io/