# test if point is inside tetrahedron

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say you have a tetrahedron made out of points a, b, c and d. What's a quick way to test if a 3D point p is inside this figure? Thanks. P.S. It's also fine if the sides ab, ac and ad are made infinitely long so that you get an infinitely large tetrahedron.

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You have four planes defined by the four cominations of three points. Take each plane equation defined by the normals, and if p lies on the side opposite of the normal for each plan then it's inside the tetrahedron.

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Given your PS, another thing to do would be to convert the point to barycentric coordinates. If any of the last 3 coordinates is negative, the point is outside the infinitely extended tetrahedron. Additionally, if the first coordinate is negative, the point is outside the original tetrahedron.

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