**Next message:**Steve_Farentinos: "Re: Converting point cloud data to UG"**Previous message:**dickman@cinti.net: "Converting point cloud data to UG"**Maybe in reply to:**Atul Damani: "Polygon"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

*> From agd4@psu.edu Mon Mar 10 16:33:54 1997
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*> X-Sender: agd4@email.psu.edu
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*> X-Mailer: Windows Eudora Light Version 3.0.1 (32)
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*> Date: Mon, 10 Mar 1997 16:29:56 -0500
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*> To: rp-ml@bart.lpt.fi
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*> From: Atul Damani <agd4@psu.edu>
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*> Subject: Polygon
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*> Mime-Version: 1.0
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*> Sender: owner-rp-ml@bart.lpt.fi
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*>
*

*> Hi EveryBody
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*> I need some help for a project I am working on. The problem is as follows
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*> Given two simple polygons A & B of any shape with or without holes how do
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*> we compute the union , intersection and A-B or B-A . If anybody could point
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*> me towards some good literature or better still some source codeI would
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*> really appreciate it.
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*> Thanks a lot
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*> Atul Damani
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*>
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*>
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*>
*

The problem is described in the computer graphics books.

If you think about it in two dimensions, you can use the illustration below:

-----

| A |

| |

----+-----+----

| | | |

| ----- |

| B |

---------------

consider the two objects A and B. To get the union, you start on one

border of A that does not belong to B. Move along the border in one direction

until you reach the intersection with B. At this intersection, continue

on the border of B in the same direction (normal pointing to the outside on

either right or left) until you reach again the intersection with A. Jump onto

A, and continue until you end up back at your starting point.

For intersection, you do the same thing, but start at a point common to both

objects.

For difference, you start on A for instance, move in a certain direction,

and at the intersection point, change direction on the next object.

If you have holes, the same type logic can be used. For 3D objects, you

can extend this logic to polygons, take their intersection, and decide which

to keep, and which to discard.

Hope this helps.

--- Georges M. Fadel Associate Professor Mechanical Engineering Department Tel: (864) 656-5620 Clemson University Fax: (864) 656-4435 Clemson SC 29634-0921 USA e-mail: gfadel@eng.clemson.edu www: http://design.eng.clemson.edu/dmg/people/faculty/fadel.html

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