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*Subject*: Re: IDLanROI Confusion*From*: davidf(at)dfanning.com (David Fanning)*Date*: Wed, 4 Apr 2001 21:20:44 -0600*Newsgroups*: comp.lang.idl-pvwave*Organization*: Fanning Software Consulting*References*: <MPG.153532f5334705a5989dc6@news.frii.com> <onitkkcp6b.fsf@cow.physics.wisc.edu> <986428514.198656@clam-ext>*Xref*: news.doit.wisc.edu comp.lang.idl-pvwave:24365

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

**References**:**IDLanROI Confusion***From:*David Fanning

**Re: IDLanROI Confusion***From:*Craig Markwardt

**Re: IDLanROI Confusion***From:*Mark Hadfield

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