Propagation of WCS Information

KAPPA applications that create an output NDF on the basis of a given input NDF usually copy the contents of the WCS component  from the input to the output, modifying it as appropriate to take account of any linear mapping of pixel co-ordinates introducing by the application. The following are exceptions to this rule:

• Applications in which positions in the output NDF are not straight-forwardly related to corresponding positions in the input NDF (e.g. ELPROF, CHAIN, RESHAPE).

• Applications in which the output NDF is not a direct representation of the input NDF (e.g. FOURIER).

The output NDFs produced by such applications will contain no WCS component  (but they will still have the four standard Frames--GRID, FRACTION, PIXEL and AXIS--albeit the AXIS Frame will probably just describe pixel co-ordinates since these applications will not usually copy the AXIS structures either).

The application WCSCOPY can be used to copy the WCS component from one NDF to another, optionally introducing a linear transformation of pixel co-ordinates in the process. This can be used to add WCS information back into an NDF that has been stripped of WCS information by one of the above applications.