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This command converts the measured X, Y coordinates to RA and Dec. It uses the transformation parameters computed by the command ASTROMET/TRANSFORM. The input is a table containing the XY coordinates which must have been processed previously by ASTROMET/TRANSFORM in order to have the descriptors with the transformation parameters set.

The user can choose among various options for doing the coordinate transformation. The output table will contain the computed coordinates. This table can be used as standard stars table in case a multi step astrometric calibration is needed.

ASTROMET/COMPUTE computes the RA,Dec coordinates from X,Y coordinates directly from the transformation parameters, while it obtains X,Y from the RA,Dec ones in an iterative manner. Also note that the equinox of the computed coordinates is the same as the standard star catalogue (which is NOT necessarily the same as its epoch) and is 2000.0 in case the PPM catalogue is used.

Petra Nass