The astrometry is determined either by you supplying explicit values for certain projection parameters, or by you providing the sky and corresponding image co-ordinates for a set of positions (see Parameter POSITIONS). In the latter case, the projection parameters are determined automatically by searching through parameter space in order to minimise the sum of the squared residuals between the supplied pixel co-ordinates and the transformed sky co-ordinates. You may force particular projection parameters to take certain values by assigning an explicit value to the corresponding application parameter listed below. The individual residuals at each position can be written out to a logfile so that you can identify any aberrant points. The RMS residual (in pixels) implied by the best-fitting parameters is displayed.
If a FALSE value is supplied, then the WCS information will be stored in the form of a standard NDF WCS component which will be recognized, used and updated correctly by most other Starlink software.
If a null value (!) is supplied, then a TRUE value will be used if the supplied NDF already has an IRAS90 extension. Otherwise a FALSE value will be used. [!]
The following synonyms are also recognised: "All_sky" -- Aitoff, "Cylindrical" -- Lambert, "Tangent_plane" -- Gnomonic.
See SUN/163 for descriptions of these projections. A null value causes the projection to be determined automatically from the data supplied for Parameter POSITIONS. [!]
KAPPA --- Kernel Application Package