Sign in to follow this  

Concave Edge Detection

This topic is 3043 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

That's not a meaningful question. Two non-parallel planes intersect at a line.. if you take a half-plane from each, bordered by the intersection line, then the question of whether the edge is convex or concave comes down to which half-planes you pick.

Share this post


Link to post
Share on other sites
I had a similar problem with triangles a few weeks ago. I wanted to determined if the edge between two adjacent triangles was concave or convex. What I did, was to project the non-shared vertex of one triangle into the normal of the other triangle. This way I was able to determine if the other triangle was below or above the plane on which the other triangle lies. So what you could do is pick a point "x" on the edge and a point "p" on the first plane (on the side of the edge you want to evaluate). Then, get the normal "n" of the other plane. After that, all you have to do is:

dotp(p-x, n)

If the result is positive then it's concave and if the result is negative it's convex. I'm not sure if it's exactly what you wanted, but I hope it helped.

Frounk

Share this post


Link to post
Share on other sites
Frounk, that makes sense. I am working with polygons rather than triangles, but they are always guaranteed not to be coplanar (or else they would have been merged into one larger polygon) and to share an edge (or else I would not be checking them against each other).
So I can apply the same technique.

Thank you.


L. Spiro

Share this post


Link to post
Share on other sites

This topic is 3043 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this