[evlatests] Problems with Shadowing

[Bryan Butler]

if you tell FILLM not to use the flag in the archive record, but to 
rather calculate its own shadowing, do you see exactly this same effect?

	-bryan


Rick Perley wrote:
>     I reported at the Monday meeting that there appear to be troubles 
> with the identification of shadowed antennas, in that some antennas, 
> when clearly in a shadowed geometry, were not being flagged as such.
> 
>     I have now a much clearer picture of the problem.  I filled the data 
> with all shadow flags off, and selected a time at which the source 3C138 
> was setting at an elevation of 20 degrees -- the azimuth is very close 
> to 275 degrees. 
>     Antenna 1 is at W1, antenna 22 is at W2, antenna 11 is at E3, 
> antenna 21 is at E2, and antenna 20 is at N1. 
> 
>     By looking at the (u,v) coordinates, it is easy to see that:
> 
>     Antenna 1 is shadowed by antenna 22
>     Antenna 11 is shadowed by antenna 21
>     Antenna 21 is shadowed by antenna 20.
>    
>     So, antennas 1, 11, and 21 should be flagged, and antennas 20 and 22 
> should not.
> 
>     But in the database, the situation is exactly reversed!  Antennas 
> 20, 21 and 22 are flagged, and antennas 1 and 11 are not.   It seems 
> clear that the shadow algorithm has the direction of the baseline -- at 
> least in some cases -- backwards.    I suspect that in cases where the 
> lower-numbered antenna is the one that is being shadowed, the shadow 
> flags are attached to the higher numbered antenna instead. 
> 
>     Rick
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