[evlatests] Image Rotations

[Rick Perley]

    It was learned some time ago that imaging with WIDAR data created 
maps that were, for some bands, reflected about the origin.  That is, 
the derived image is rotated 180 degrees about the phase center.  This 
was not true at all bands -- X-band showed the correct orientation.  The 
origin of the problem was quickly ascertained, and a correction put in.  
Data were taken yesterday to determine if this fix is right.   We 
observed Cyg A for an hour at X and C bands.  To ascertain the 
orientation, the phase center was placed on the southern hotspot of this 
(mostly symmetric) source. 

    Ken stated, yesterday:

I expect the correct orientation to be the reflected one.  I also
expect that it will be the same for C and X bands.  If all that is
borne out, then we ask Martin to coerce his phase convention.

    And Ken is correct.  The orientations are now the same at both X and 
C bands -- are are rotated by 180 degrees. 

    I will also point out that due to the issue discovered by Vivek 
yesterday (large sawtooths in the phase at X-band, getting worse with 
increasing subband number), imaging at X-band is very difficult -- the 
ragged phase could only be corrected for subband 1 -- all others are so 
violent that CALIB failed.  The origin of the problem is understood by 
Ken and Barry.