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Re: IDLanROI Confusion

Mark Hadfield (m.hadfield@niwa.cri.nz) writes:

> > What happens if you make the circle much much bigger?  I think then
> > the answers will converge to what you expect.
> I don't.
> Consider a pixelated diagonal line segment. The length along the pixel edges
> will exceed the true (along-diagonal) length by sqrt(2), however fine you
> pixelate it.

Well, I've done the experiment (easy with IDL :-)
and I find that the area seems to converge, but
the perimeter seems to remain about 15-17% larger
than I expect it to be. I am now trying to 
figure out a clever way to add up the straight
line distance between points without using a loop.
(And without resorting to JD.) I'll let you know
what I find. :-)



P.S. Let's just say that 15% is probably right at the
border of the other, unavoidable, errors in my analysis,
but it is big enough to worry me.

David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155