Re: WCS alignment

Posted by karenacollins on Feb 05, 2013; 1:03am
URL: http://astroimagej.170.s1.nabble.com/WCS-alignment-tp19p24.html

Hi Russ,
    I was able to retrieve the 3 images just fine. The headers on these images do have WCS data (RA---TAN and DEC--TAN) and work properly in both AIJ and DS9. I loaded all three and made a composite image with no problem (all 3 are aligned fairly well to start with), so you are set for the first part of your project. If you haven't worked out the steps to build a color composite from 3 separate images, I could write up a quick list of steps for you.
   To make your multi-wavelength project work, I think it is a matter of AIJ ignoring AXES 3 and 4 in the radio data and providing a feature to align/scale/rotate based on WCS. The current AIJ alignment routine relies on centroids of stars for alignment and only works when images are of the same scale and rotation, and when they are aligned within the radius of a specified aperture (which can be arbitrarily large as long as the field is sparse around the alignment stars selected). I hadn't considered dealing with the the scaling and rotation part when using WCS, so I will need to look into how difficult those will be to implement.  I am currently working in the WCS area of the code, so I will try to get back to you in a couple of weeks with the likelihood of being able to implement WCS alignment in time for your class.

Karen

On 2/4/2013 7:11 PM, rkohrs [via AstroImageJ] wrote:

"karenacollins [via AstroImageJ]" <[hidden email]>
writes:

>    Thanks for the information. The radio image uses SIN projection
>for RA and DEC (see CTYPE1 and CTYPE2 in the header) so we are good
>there. However, the it has 4 axes (RA, DEC, FREQ, STOKES) and AIJ can
>currently only deal with 2 axes (RA and DEC). The best possibility here
>is that I might be able (not sure) to ignore the FREQ and STOKES axes if
>you are not using those.
>    I don't see any WCS info in the header for the optical image
>header you sent. It looks like the image was written by MaximDL, and I
>don't see the usual headers that MaximDL adds after a "plate solve" has
>been ran on the image. I believe Maxim uses a program called pinpoint to
>do do the plate solve work.
>    Do you have an installation of DS9 available to you? If so, when
>you open the optical image in DS9, do you see RA and DEC displayed in the
>"alpha" and "delta" boxes above the image? If so, that means I am missing
>something in the header. If you do see RA and DEC in DS9 (or don't have
>access to DS9), I would like to get a copy of this image for testing if
>possible.
>    By the way, what is your end goal after alignment? Do you intend
>to build an RGB color image from 3 different images?

On the radio end, I think that the RA and DEC are sufficient.  FREQ just
refers to the frequency of the observation and I'm not certain about
STOKES.  

I'm attaching the actual optical images for you to look at. Unfortunately,
I don't have a working version of DS9...I did at one time, but not now, so
I have no way of looking at the alpha and delta boxes myself.  Would you
be able to?

In terms of the end result, I'd like for students to create their own
composite optical image first.  Then, I'd like for them to be able to
overlay the radio on top of that.  With M42, they would then be able to
pick out the location of the HII region that is so strong in
X-Band...among other things.

My background is actually in geology, but I worked at Green Bank this past
summer as an RET for eight weeks.  We recommissioned the USNO 20m radio
telescope there and brought its operation online via SKYNET.  While I
wrote a number of lesson plans for the 20m, along with manuals, etc....I
wanted to write an investigation that required students to learn some
basic optical image processing as well as allow them the opportunity to
see regions in optical and radio at the same time.  They're not paying me
for this anymore, but I just can't let it go :)...

Let me know if the attachments make it through okay.

Dum spiro spero,

Russ Kohrs

A Husband and Father
Who teaches Geology and Astronomy...
Who insists that every rock can tell a story...
Who is transfixed by seemingly esoteric astrophysical concepts...
Who thinks of white-washed buildings and gold mosaics when he eats any
olive...
Who loves chili, particularly with pasta, hot sauce, onions, and copious
amounts of cheese...
And who would be happy to play bagpipes for your event!
http://www.wix.com/rkohrs/shenandoahpiper

You will certainly not doubt the necessity of studying astronomy and
physics, if you are desirous of comprehending the relation between the
world and Providence as it is in reality, and not according to imagination.

-- Maimonides

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