Equation for the intersection of a ray and a sphere is backwards #1191
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hollasch
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Aug 20, 2023
Trevor observed that the equation for the ray-sphere intersection was backwards in that it used (P - C) [center to ray origin] instead of (C - P) [ray origin to sphere center]. That's all well and good, but it ends up rippling all the way back to the fundamental sphere equations presented in the text. Sigh. And I couldn't resist. In flipping everything so it flows without an odd inversion in the middle, I also discovered some annoying minus signs that could be eliminated, plus some bits that needed a tiny bit more explanation. Quite a bit more work than it originally appeared, but I'm pleased with the results. Resolves #1191
hollasch
added a commit
that referenced
this issue
Aug 30, 2023
Trevor observed that the equation for the ray-sphere intersection was backwards in that it used (P - C) [center to ray origin] instead of (C - P) [ray origin to sphere center]. That's all well and good, but it ends up rippling all the way back to the fundamental sphere equations presented in the text. Sigh. And I couldn't resist. In flipping everything so it flows without an odd inversion in the middle, I also discovered some annoying minus signs that could be eliminated, plus some bits that needed a tiny bit more explanation. Quite a bit more work than it originally appeared, but I'm pleased with the results. Resolves #1191
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It's written as
(P - C)
It should be
(C - P)
The math and everything is still correct but that (-1) gets squared out, but all of the ray intersections are from the center to the ray origin. Not the other way around
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