Dear Newsgroup:
In AutoLisp the inters statement (inters pt1 pt2 pt3 pt4)
can be use to find the intersection of two lines. Where pt1 pt2 are
the end points of the first line and Pt3 and pt4 are endpoints of the
second line.
Is there way to find the intersection of lines crossing other
entities. For example, a line crossing a circle, polyline or whatever
else? I want to do this using a lisp routine would allow picking
entities but not their intersecting points. I want the lisp routine to
calculate the intersecting points. Any suggestions on how to write a
routine that would do this?
·······@juno.com
From: Francis Leboutte
Subject: Re: Lisp Routine to find intersections without picking them
Date:
Message-ID: <34011e34.3585916@news.skynet.be>
····@evansville.net (Doug Hormuth) wrote:
> Is there way to find the intersection of lines crossing other
>entities. For example, a line crossing a circle, polyline or whatever
>else? I want to do this using a lisp routine would allow picking
>entities but not their intersecting points. I want the lisp routine to
>calculate the intersecting points. Any suggestions on how to write a
>routine that would do this?
I hope that someone 'll give us pointers to Lisp source about computational
geometry. Else you can have a look at the FAQ for comp.graphics.algorithms;
it seems that a lot of CG C code is available from the Internet.
Here is an extract from this FAQ:
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Subject 0.03: How can I get this FAQ?
Here are a few locations that have the FAQ:
ftp://rtfm.mit.edu/pub/faqs/graphics/algorithms-faq
ftp://ftp.seas.gwu.edu/pub/rtfm/comp/graphics/algorithms/comp.graphics.algorithms_Frequently_Asked_Questions
http://www.cis.ohio-state.edu/hypertext/faq/usenet/graphics/algorithms-faq/faq.html
The latest addition, an up-to-date HTML version:
http://www.exaflop.org/computing/faqs/cga.html
The (busy) rtfm.mit.edu site lists many alternative "mirror" sites.
The ohio-state site is sometimes out of date.
Also can reach the FAQ from http://www.geom.umn.edu/software/cglist/,
which is worth visiting in its own right.
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Francis Leboutte, Algorithme, Rue de la Charrette 141, 4130 Tilff, Belgium
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