Unity Quaternion - get Euler angles of a component B relative to component A

Question

I cannot get my head around Quaternions, and have tried many combination of operators on this (after reading / viewing tutorials). No success - just shows my lack of understanding. Even tried it with angles and atan2() - but all that really showed me was what gimbal lock was. The problem I am trying to solve is:

I have a component (say A, a cube) with some rotation in the world frame of reference (doesn't actually matter what that rotation is, could be orientated any direction).

Then I have another component (say B, another cube) elsewhere in the world space. Doesn't matter what that component's rotation is, either.

What I want to get to in the end are the (Euler) angles of B relative to A, BUT relative to A's frame of reference, not world space. The reason is I want to add forces to A based on B's direction from A, which I can then do with A.rigidbody.addRelativeForce(x, y, z); .

Stuck.

Can you use something like A.transform.InverseTransformDirection or A.transform.InverseTransformVector? — Dave, Jun 06 '20 at 09:07

nmw01223 · Accepted Answer · 2020-06-10T16:43:14.680

With thanks for the comments, I think I have it.

For reference, considering a vector and rotation within the same (world frame) coordinates, a new vector representing the original, but viewed from the perspective of local frame coordinates, being those of the original world rotation, can be calculated as:

static Vector3 createVectorForLocalRotationFrame(Vector3 worldVector, Quaternion worldRotation, bool normalise)
{
    Vector3 localVector = Quaternion.Inverse(worldRotation) * worldVector;

    if (normalise)
        localVector.Normalize();

    return localVector;                                                             
}

The normalise option is just something I needed. Don't ask me how it works, but it appears to be right.

Unity Quaternion - get Euler angles of a component B relative to component A

1 Answers1