I For colision purposes, the 3 dimensional shape which comes nearest to a human form is a 3D elipsoid. Right? Well... it's quite easy to perform colision detection with polygons whose normal's are perpendicular or paralel to the elipsoide. The problem is when the normal of the polygons isn't in none of this 2 cases. The easiest way is to check if every point of the polygon is inside the elipsoid, but what if some part of the polygon touches or is inside the elipsoid, but none of the points which define the polygon aren't? Anyone knows hot to perform this type of colision? I'd also like to know, which exact points or area of the polygon interesected with the elipsoid. thanks Edited by - wolverine on 9/22/00 9:24:50 AM

Hmmm...interresting...but this might not be so easy...

You need 2 equations to start with:
A- Elipsoid equation...sorry can''t remember this one...
B- Plane equation: Ax + By + Cz + D = 0

Next combine those 2 equations, and you end up with an equation. Fill this one in, and voila. The exact collision can be:
- None - the equation can not be resolved - no collision
- Point - the side of the elipsiod touches the plane.
- Elipse - and elipse on the plane and on the elipsoid. Perfect collision intersection found

Next is to find out if this elipse is on the polygon. Best is to project the polygon to 2D space...
Then I''m lost...
? Maybe approximate by using some triangles instead of the elipse... ?
? Maybe you could test the upper-lower-left-right side of the elipse as points in polygon, and also test the polygon vertices if they''re inside the elipse - but this is going way over my head...

Can someone please take over...

I can''t help personally but there was an article on flipcode.com awhile back that deals with using ellipsoids for collision detection.

Check it out:

http://www.flipcode.com/tutorials/tut_coll-ellipsoids.shtml

That should be what you want.

baskuenen : i had thought in projecting both the elipse and the polygon in a 2D space and then seing if some points of the polygon were inside the elipse. but i had to do this projection in 3 planes ( xy, yz, xz ) and then joining all the info and take conclusions. i thought there might be a better way.

Promiscuous Robot : nice tutorial. i need to take a better look at it and see what i can use.

thanks for the help guys.