Transformations

The TRANSFORM facility stores the information which it requires for conversion between different coordinate systems in HDS structures called transformations. They have an HDS type of TRN_TRANSFORM¹and the purpose of each of these structures is to describe the relationship which exists between two different coordinate systems. The two systems in question are termed the input and output coordinate systems and the HDS transformation structure serves to ``link'' them together as a pair. In this role, the transformation may be regarded simply as a ``black box'', thus:

Positions (or points) in each coordinate system will be specified by appropriate sets of coordinates, and the purpose of the transformation is to define an ``association'' between corresponding points in each system. Thus, given the coordinates of a point in one system, the coordinates of the associated point in the other system may be derived by using the information stored in the transformation structure.