[daip] FLATN help

[Eric Greisen]

Julie Grant wrote:
> Hi,
> 
> I am trying to create a mosaic using several individual pointings.  Each 
> pointing is made up of several facets and then joined together using 
> flatn.  For the large mosaic I want to include all pointings with data 
> only out to 15 arc-minutes in radius of the L band primary beam.  What 
> is the best way to approach this?
> 
> I have tried using FLATN and the edgskp parameter.  However, I cannot 
> seem to get this to work properly.  Each pointing is 4096x4096 pixels 
> and each pixel is 1 arcsecond.  So I have placed edgskp = (4092/2)-900 = 
> 1148 where 900 is 15 arcminutes in pixels.
> 
> Am I on the right track or is there another AIPS task that would work 
> for this problem?

I would have said that you are on the right track - EDGSKP is designed 
to drop the weight abruptly to 0.0001 outside a circle of radius nx/2 - 
edgskp which sounds like what you want.  Note that the outer pointings 
will have image values all the way the the edge since they are the only 
image at those locations and the weight no longer matters.  The primary 
beam parameters may also be used to cut off the images - set e.g. PBPARM 
= 0.1, 0 to use the VLA beam but stopping if its value is less than 0.1.

Eric Greisen