[daip] New Staff Reply - [!POR-156771]: World coordinates of CC components

[Eric Greisen]

New Staff Reply: World coordinates of CC components

The header shows both the "observed" coordinates - which are the coordinates
toward which the antennas pointed - and the header "coord" value which are
the coordinates of the phase stopping point.  CC components coordinates are
wrt to the latter.  They are in degrees and the RA term is corrected by the
cosine of the phase stopping declination.  Thus

RA = RA(phase center) + DeltaX/cos(DEC(phase center))
DEC = DEC(phase center) + DeltaY

When you do multi-facet imaging with DO3D TRUE, each facet has a different
phase stopping point.  DO3D false uses the same phase stopping point for
all facets, leading to very large offsets in some of the CC files on occasion.

The verb IMHEADER shows the phase stopping coords in the table of various
coordinates and, if the observed position differs from the phase stopping one, 
also shows the observed position.

Eric Greisen


Ticket Details
===================
Ticket ID: POR-156771
Department: AIPS Data Processing
Priority: Default
Status: Closed
Link:  https://help.nrao.edu/staff/index.php?_m=tickets&_a=viewticket&ticketid=1741