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Re: Points in a rectangle with an angle [message #48229 is a reply to message #48228]

Wed, 05 April 2006 09:58

Rick Towler
Messages: 821
Registered: August 1998

Senior Member

This is the classic point in polygon test. There are two common
approaches, the crossing test and the winding test. You can google this
for the specifics but here are a few pages to get you started:

http://softsurfer.com/Archive/algorithm_0103/algorithm_0103. htm

I've used this in the past:

http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/p npoly.html

There are probably ways to IDLize this but I implemented this in a DLM
so I never gave it any thought.

I would suggest a 2 stage approach:

first do your rough cull using WHERE to get a subset of points that
*may* be in your polygon. Then do the fine cull with a point in polygon
test of your choosing. You have a pretty simple case (2d, 4 vertex
polygon) so you could get away with a pretty simple test.

-Rick

JJMeyers2@gmail.com wrote:
> Hello,
>
> I have a problem in IDL that I was wondering if anyone has any idea how
> it can be done.
> I have a set of coordinates and I am trying to figure out how many of
> the coordinates are inside a rectangle. I know the coordinates of the 4
> edges of the rectangle but the problem is that the rectangle is at an
> angle in the x,y axis ( I know the slope). I can not just say
> coords=where((x LE xmax) AND (x GT xmin) AND (y LE ymin) AND (y GT
> ymax))
> because that will give me coordinates of a rectangle without an angle
> (parallel to the y axis).
> Is there any function in IDL that might be doing that?
>
> Thank you,
> JJM.
>

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[Message index]

		Re: Points in a rectangle with an angle By: Maarten[1] on Thu, 06 April 2006 04:37
		Re: Points in a rectangle with an angle By: Craig Markwardt on Wed, 05 April 2006 09:53
		Re: Points in a rectangle with an angle By: JJMeyers2 on Wed, 05 April 2006 10:08
		Re: Points in a rectangle with an angle By: K. Bowman on Wed, 05 April 2006 09:43
		Re: Points in a rectangle with an angle By: Rick Towler on Wed, 05 April 2006 09:58
		Re: Points in a rectangle with an angle By: David Fanning on Wed, 05 April 2006 09:48

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