Basic Principles Using the PE API PE Entity Reln Diagram

The Projection Engine (PE) defines and transforms coordinate systems for ArcSDE. It supports predefined and application-defined coordinate systems and isolates map projection and datum-handling code into a compact, easily integrated program for managing coordinate systems through a well-defined, open API.

Thus, the ArcSDE Projection Engine has two purposes:

1. Defining coordinate systems
2. Transforming data between coordinate systems

All spatial data has a coordinate system and comes from many different sources, which means you may have to change the coordinate system to combine data for display or storage in a database. Towards this end, the PE includes predefined coordinate systems and transformation methods that allow you to create your own coordinate systems and implement your own transformation functions. In ArcSDE, predefined coordinate systems are accessed with integer codes and are listed in the pef.h file in the include directory under the ArcSDE home directory.