| Re: IdlGrPolygon - Intersection with planes and lines [message #32937 is a reply to message #32936] |
Tue, 19 November 2002 15:54  |
Rick Towler
Messages: 821
Registered: August 1998
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Senior Member |
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"Martin Downing" <martin.downing@ntlworld.com> wrote
> Hi all,
>
> Has anyone written code they wish to share which will give the
intersection
> of a polyon surface* with a 3D plane, and also the intersection of a
polygon
> surface with a line (3d ray)?
> One object graphics way to do the plane intersect could be to transform
the
> object to map the plane of intersection onto the z = 0, then use a very
> small zclip range and the result would be given in image form, however I
> would very much like the "exact" geometric solution, i.e the intersect as
a
> polyline for the plane and point(s) for the line (kind of graphics gems
type
> stuff)
Hi Martin,
Could you double mesh_clip the surface? The resultant mesh would still be a
polygon though. Or, could you mesh_clip, where() the verts that lie on the
clipping plane, and somehow reconstruct the polyline connectivity? That
last bit might be sticky.
I've been playing with some polyhedron/box intersection code. Not what you
are looking for, but in my search I have found a few resources which might
be helpful if you can't find an all IDL solution.
There is the magic software archive:
http://www.magic-software.com/Intersection3D.html
which is a large C++ archive of many 3d graphics routines. I know he has a
plane/ plane intersection test which returns the line of intersection which
you could use if your surface was meshed with quads. I played around with
some of the magic code in a dlm. You have to work a bit to get the data
into a form that works with his classes and buy the book if you want any
decent docs, there are few comments in the source.
Realtime Rendering:
http://www.realtimerendering.com/#isect
A section on intersection testing. Has some of the links I have provided.
Also links to this on the same site:
http://www.realtimerendering.com/int/
This web page has a table of static object intersection testing methods. It
lists a few sources for triangle/triangle tests which you could use if your
surface was meshed with tris.
There is also the Graphics Gems archive:
http://www.acm.org/tog/GraphicsGems/
This page might be helpful in tracking down which gem you'll need to get
from your local library. I can tell you that there is little on this in
Gems V. I also can tell you the Gems source code is where you'll probably
want to start. It is implemented in C and tends to be very straightforward.
Easier for us IDL'ers to chew on.
Hopefully this will get you started.
-Rick
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