| Re: Fractional Pixels Origin? [message #47634 is a reply to message #47583] |
Fri, 17 February 2006 07:24   |
CJCrockett
Messages: 3
Registered: February 2006
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Junior Member |
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Wow....thank you so much for all your replies, though I'm not quite
sure how to digest all of it.
The fractional pixels are the output of locating the centroid of a
comet in an image. The centroid then defines my center from which I
calculate aperture photometry. In the interest of getting the most
accurate results, I am using fractional pixel areas and hence need to
know where to start counting from "inside" the pixel.
Our images are in the FITS format, as a previous poster indicated. But
the centroiding algorithm knows nothing of FITS, it just receives a 2-d
image array and goes to town. If anyone has any familiarity with
astronomy libraries, I am using the CNTRD procedure in the Goddard
library which in turn uses DAOPHOT.
I understand now that there are several different conventions in use
(and my data set may actually be using two different conventions as
they are from two different sources)! I know that one source puts 0,0
at the center of the pixel. My data, using CNTRD, I don't know about.
Is there a test of some sort I can do to clear up the confusion?
Thanks again for the responses!
Regards,
Christopher Crockett
University of Maryland
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