[daip] Coordinate system of antenna table in FITS file produced by FITTP

[Eric Greisen]

Bojan Nikolic writes:

 > Thanks again for the swift reply.  Sorry to go on about this but it is
 > quite important for what I'm doing at the moment and I appreciate your
 > help with this.  

   I am off on vacation following today - so now or much later.

 > 
 > I do not understand precisely what you mean when you say "Bx, By, Bz
 > are local to the array center" (let's concentrate on the case of the
 > VLA and ignore VLBI now).  Bx, By, Bz can not I think be with
 > reference to the tangent plane at the array centre since I can see a
 > large dispersion in Bz in the file I mentioned.

There are both earth curvature and local topography.  The earth is so
curved that the entire antenna disappears when it is well out an arm.

If you want to know more about this you will have to consult experts
which I am not.  AIPS uses in UVFIX the antenna coordinates and you
could consult that code.  AIPS does not change the coordinates in any
way other than to offer the option to make minor delta Bx, etc changes
to station position and phases.

There are folks at GMRT and ATCA probably who understand this and
ksowinsk at nrao.edu is perhaps the most knowledgable about this at the
VLA.  Ken is pretty knowledgable but his job is the real-time control
system not astrometry.  lkogan at nrao.edu is the programmer of UVFIX.

Eric Greisen