Determining circularity

[Todd Clements <mole6e23(at)hotmail.com>]

Hi all...

I was wondering if anyone knew of routines to determine the circularity 
of an image. We have images from our detector and for optimal 
calibration, they need to be as circular as possible, and it's difficult 
to tell by eye when it's close but not quite there.

Generally these images have fairly well defined edges, although there is 
definitely some gray area as to what consistutes the edge, which makes 
it difficult to determine by eye sometimes.

Basically, I guess it comes down to fitting the edge of the image to an 
ellipse, but there has to be some determination of what the edge is as 
well.

Any pointers to what might already exist would be most helpful... this 
qualifies as one of those it would be nice to have but we've lived 
without it this long type of things. I glanced through the libraries 
referenced by David's home page, but couldn't find anything.

Thanks!
Todd