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0 pointsLegionMammal9781y ago0 comments

Does leaving them unnormalized affect their numerical accuracy? A few sources [0] [1] suggest renormalizing often, but I'm not sure whether it's just dogmatic or if it's actually necessary. It definitely seems less involved than re-orthogonalizing matrices, in any case.

(Luckily, for my project, I'm not particularly worried about error, since the only thing being rotated frequently is the camera, and microscopic scaling and shearing won't affect the result much. I measured the error in the basis vectors over time to make sure, and it just seems to be O(sqrt(t)) random-walk noise, not anything that compounds on itself.)

[0] https://www.tobynorris.com/work/prog/csharp/quatview/help/or...

[1] https://stackoverflow.com/a/12934750

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xeonmc1y ago

As I mentioned, unnormalized quaternions just adds an extra uniform scaling, so it’s just a matter of dividing the final vertex by qq* to remove the scaling.

EDIT: I guess if you use a shitty overzealously reduced version of the quaternion formula then you absolutely need to normalize it constantly, because the reduced formula assumed three degrees of freedom (completely defeating the purpose of using quats in the first place), normalization is then to solve a problem that you caused. But if you use a proper formula then my recommendation is actually that you never normalize your quats, instead only un-scale your vertex at the end.

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