Cartographic projection filter and library (datum package) Proj and invproj perform respective forward and inverse transformation of cartographic data to or from Cartesian data with a wide range of selectable projection functions (over 100 projections). Geod and invgeod perform geodesic (Great Circle) computations for determining latitude, longitude and back azimuth of a terminus point given a initial point latitude, longitude, azimuth and distance (direct) or the forward and back azimuths and distance between an initial and terminus point latitudes and longitudes (inverse). This package contains auxiliary projection datum grids used by the library and tools.