Re: [APML] Giant Scorpius Tail Montage

[Ray Butler <ray.butler@nuigalway.ie>]

Chris,

That's an excellent mosaic. I don't see any seams resulting from 
intensity scaling issues, which is impresssive! However, along the 
junction between the top and middle panels, there is a curious geometric 
distortion - everything looks slightly stretched. Since I don't see the 
same thing on the other junction, it can't be related to the schmidt 
camera optics - I think it must be in the processing.

This distortion reminds me of what I used get if I screwed up a 
high-order geometric transformation (registration) between two images in 
IRAF. E.g. if one of the tie-points I entered - supposedly the same star 
on the 2 images - was actually 2 completely different stars, due to a 
mixup on my part. The software does its best to fit the transformation, 
but since it is based on flawed positional input, it ends up causing 
distortion like that. I used have to go back through the list of 
tie-points to track down my star mismatch. (Later on, I realised that I 
could ask to software to use automatic statistical rejection of dodgy 
tiepoints...which weeded out any error on my part! (;0)).

I wonder if you had a similar problem with your mosaicing software? Did 
you have to tell it which stars were in common on the two images, or 
does it do some automatic pattern recognition to register the images? 
Even in the latter case, things can go wrong...

Ray "who believes that humans still beat computers at visual pattern 
recognition - but also that we are a tad more prone to mental fatigue" 
Butler

-- 
Dr. Ray Butler
Lecturer, Physics Department & Computational Astrophysics Laboratory,
National University of Ireland - Galway, 
University Road, Galway, Ireland. 
Web: www.nuigalway.ie/physics/ 	Email: ray.butler-AT-nuigalway.ie 
Tel: +353-91-493788 		FAX: +353-91-494584

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