# Closest poing on Ray to Frustum?

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Hi Everyone, Does anyone know a good closest point on ray to frustum test? I looked through my handy "Real time collision detection" book and was unable to find anything immediately helpful. I'm really looking to find 2 things... #1) Does a ray intersect the frustum. #2) If not, how close does it get Thanks (:

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I done a google search and this topic has come up on this forum before:

Ray Frustrum Intersection

Hope this helps [smile]

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Heya Render,

I saw that post too, which talks about whether a ray intersects or not but there is no "closest point" calculation talked about there unfortunately.

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In chapter 3, section 10 of Real-Time Collision Detection, Ericson describes the concept of Voronoi regions. Basically, each feature of the frustum (vertexes, edges, faces) has a region of space associated with it such that all points in this space are closer to that particular feature than any other feature.

What you can do is calculate these Voronoi regions and then analyze the ray as it passes through each one, finding the shortest distance between the ray and the feature associate with that region. Once you find the closest feature, you can find the closest point on that feature (if you didn't already in the previous step). What's nice is that this process also handles the collision case, since in such cases the closest distance will be zero and the closest point will be the point of collision.

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Zipster thank you so much!

I never understood what the Voronoi regions were about but that clarifies it quite a bit.

Thanks man

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i was about to say, Christer is normally pretty thorough.

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Yeah definitely. At the 2 studios I've worked at, it's the "go to" book for the good solutions to collision detection type issues.

Really great book

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