MeqParAngle

A MeqParAngle node computes the Parallactic Angle for a source at a given Right Ascension and Declination (first child) as seen for a telescope at a particular location (second child). You must provide this mode with a location. This can be done in two ways. If you instantiate the node with the name of an observatory known to aips++, then the location of the observatory, in ITRF coordinates, is used for the transformation. If you do not supply the node with an observatory name, then you must supply the ITRF X,Y,Z cooordinates of the station location (second child - normally a MeqComposer with the ITRF X Y and Z coordinates as children. Since modern synthesis telescopes may consist of stations hundreds of kilometres apart, you will (at least theoretically) improve your analysis by computing the parallactic angle on a station by station basis rather than using a single 'observatory' position.