quaternions

I'm having trouble finding any good information on this topic. Basically I want to find the component of a quaternion rotation, that is around a given axis (not necessarily X, Y or Z - any arbitrary unit vector). Sort of like projecting a quaternion onto a vector. So if I was to ask for the rotation around some axis parallel to the quaternion's axis, I'd get the same quaternion back out. If I was to ask for the rotation around an axis orthogonal to the quaternion's axis, I'd get out an identity quaternion. And in-between... well, that's what I'd like to know how to work out :) sebf I spent the

I am trying to rotate a group of vectors I sampled to the normal of a triangle If this was correct, the randomly sampled hemisphere would line up with the triangle. Currently I generate it on the Z-axis and am attempting to rotate all the samples to the normal of the triangle. but it seems to be "just off" glm::quat getQuat(glm::vec3 v1, glm::vec3 v2) { glm::quat myQuat; float dot = glm::dot(v1, v2); if (dot != 1) { glm::vec3 aa = glm::normalize(glm::cross(v1, v2)); float w = sqrt(glm::length(v1)*glm::length(v1) * glm::length(v2)*glm::length(v2)) + dot; myQuat.x = aa.x; myQuat.y = aa.y; myQuat

I have two vectors u and v. Is there a way of finding a quaternion representing the rotation from u to v? Polaris878 Quaternion q; vector a = crossproduct(v1, v2); q.xyz = a; q.w = sqrt((v1.Length ^ 2) * (v2.Length ^ 2)) + dotproduct(v1, v2); Don't forget to normalize q. Richard is right about there not being a unique rotation, but the above should give the "shortest arc," which is probably what you need. Half-Way Vector Solution I came up with the solution that I believe Imbrondir was trying to present (albeit with a minor mistake, which was probably why sinisterchipmunk had trouble verifying