Category Archives: Mathematics

Exact Bounding Boxes for Spheres/Ellipsoids

Finding the tightest axis-aligned bounding box for a sphere is trivial: the box extends from the center by the radius in all dimensions. But once the sphere is transformed, finding the minimal bounding box becomes trickier. Rotating a sphere, for example, shouldn't change its bounding box, but naïvely rotating the bounding box will expand it unnecessarily. Luckily there's a trick to computing minimal bounding boxes by representing the transformed sphere as a quadric surface.

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A Beautiful Ray/Mesh Intersection Algorithm

In my last post, I talked about a beautiful method for computing ray/triangle intersections. In this post, I will extend it to computing intersections with triangle fans. Since meshes are often stored in a corner table, which is simply an array of triangle fans, this gives an efficient algorithm for ray tracing triangle meshes.

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Solving Polynomials

A well known (if not by name) theorem is the Abel–Ruffini theorem, which states that there is no algebraic expression for the roots of polynomials with degree higher than 4.

A not-so-well-known fact is that for any polynomial \(P(x)\), it is possible to find (with exact arithmetic) a set of ranges each containing exactly one root of \(P(x)\). One such algorithm is due to James Victor Uspensky in 1948. Continue reading Solving Polynomials