The Projection Engine is a developer's library that provides map projection and datum transformation support. The data model is derived from a modified version of the original European Petroleum Survey Group's (EPSG) coordinate system model.
The Projection Engine was first incorporated into ArcSDE 3. It has since been used in MapObjects 2, the ArcView Projection Utility, ArcPad, and ArcGIS 8 and later versions.
EPSG also publishes a database of coordinate system information plus related documents on map projections and datums.