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Re: data inside a circle [message #44533 is a reply to message #44357]

Tue, 21 June 2005 05:01

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

Ben Tupper wrote:
...
> I guess I am a bit late with this but the following is from the online
> help to IDL 6.1
>
> " The IDLanROI::ContainsPoints function method determines whether the
> given data coordinates are contained within the closed polygon region."
>
> So, you could define the circle boundary as the ROI and pass the points
> to the object method.

A circle is not a closed polygon. It can be approximated with arbitrary
accuracy by a closed polygon with a sufficiently large number of sides.
However, as long as you use a finite number of sides, there will always
be a certain amount of inaccuracy in that approximation. The more sides
you use, the slower the comparison; at some desired level of accuracy,
it's quicker to perform the correct test for being inside a circle,
than it is to test for being inside a polygon approximation to a
circle.

In any event, the key problem in this particular problem is not the
test for being inside a single cirle; the problem is that the test is
against a very large number of circles. Doing that efficiently in IDL
is tricky; and it's not clear to me that IDLanROI::ContainsPoints helps
address that problem.

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[Message index]

		data inside a circle By: angela on Fri, 10 June 2005 14:01
		Re: data inside a circle By: Michael Wallace on Mon, 13 June 2005 17:10
		Re: data inside a circle By: btt on Mon, 20 June 2005 06:18
		Re: data inside a circle By: Michael Wallace on Mon, 13 June 2005 09:20
		Re: data inside a circle By: btt on Tue, 21 June 2005 13:09
		Re: data inside a circle By: James Kuyper on Tue, 21 June 2005 05:01

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