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Re: IDLanROI Confusion [message #24557]

Wed, 04 April 2001 20:20

davidf
Messages: 2866
Registered: September 1996

Senior Member

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. :-)

Cheers,

David

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

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[Message index]

		Re: IDLanROI Confusion By: davidf on Wed, 04 April 2001 20:20
		Re: IDLanROI Confusion By: Mark Hadfield on Wed, 04 April 2001 16:55
		Re: IDLanROI Confusion By: Craig Markwardt on Wed, 04 April 2001 14:47
		Re: IDLanROI Confusion By: davidf on Thu, 05 April 2001 11:18

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