J. McDowell
SAO
The high spatial resolution and complex nature of the AXAF observatory requires greater care in the handling of coordinate systems than was done in earlier high energy astrophysics missions. In particular, the concept of `detector coordinates' has been used to mean several quite different things. However, it is important to formalize our coordinate handling in a mission independent way so that it can be generalized for use by other projects. In this paper I describe the different logical coordinate systems (chip, tiled detector, instrument bench, focal plane, tangent plane, sky plane) and their applications. A complementary paper by H. He discusses the software which has been implemented to use these coordinate systems.