[daip] [#4188]: blanking in GBT maps

[Trisha]

OK, so let me make sure I understand:

   - In SDGRD I do not need to add a fake RA and Dec (I can leave APARM
   blank), and therefor after SDGRD I do not need to change the header to
   change the reference coordinate to Glong and Glat because SDGRD will be
   able to handle the coordinate information.
   - Blanking the cube will help me get better moment maps (I usually use a
   channel range; will that be enough?)
   - In XMOM I should use OPTYPE 'MAX' with ICUT=0 and FLUX=-1000000.

Thank you so much for your help!-Trisha


On Tue, Dec 24, 2013 at 5:33 PM, Eric Greisen <egreisen at nrao.edu> wrote:

> Many thanks for the FITS file - it will help me test things.
>
> I ran SDGRD on your data and am shocked at how smart it is.  It sets the
> reference declination to 0 at a correct (way offset) pixel location and
> makes a proper image whether or not one specifies APARM.
>
> But XMOM cannot be run blindly - I tried it after TRANS and found that no
> spatial pixel has a legitimate moment if one allows all image values.  All
> of them find that the predominant velocity channel is either < 1 or > N
> (probably all the < 1).  Moment analysis assumes a real and positive signal
> - with a lot of channels at values < 0, it fails.  In fact, the times I
> have done moment analysis I have blanked the cube very carefully so that
> channels that are clearly noise are omitted.  The OPTYPE 'MAX' avoids some
> of these issues and makes useful images for you.
>
> With your imaging parameters 1543 of the 1600 image pixels have values -
> the corners are missing a bit.
>
> thanks
>
> Eric Greisen
>
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