How to randomly draw Quaternions within a specific range of Euler angles for rotation?

Question

I am pretty new to Quaternions so please bear with me. I want to draw random Quaternion samples so that their Euler angle equivalent would range within [-30, +30] degrees on each axis. Currently, I know how to sample Quaternions from the full range ([-180, +180]) using the code below but I don't know how to modify the code so that I can get samples within the range [-30, +30]. Can anyone help me with that?

I'm not sure if this is helpful to answer this question but here's a piece of information: I eventually want to convert the sampled Quaternion to Euler angles an apply the Euler rotation in some 3D shapes. The order of rotation in the software I'm using to do this is XYZ meaning that it first rotates the 3D shape along the X axis, then Y axis and then Z axis.

import numpy as np
def sample_Quaternion():
    r = np.random.uniform(0, 1 - 0.001, 3)
    while np.linalg.norm(r) > 1:
        r = np.random.uniform(0, 1 - 0.001, 3) # Just to keep the L2 norm within [0, 1.0)
    w = [np.sqrt(1 - (r[0]*r[0] + r[1]*r[1] + r[2]*r[2]))]
    r = np.concatenate(r, w) # the output of this would represent (x, y, z, w)
    return r

Answer 1

The simplest way to do this would be to generate the Euler angles randomly, then use them to create the quaternion. Most existing quaternion implementations in game engines and 3D math libraries will have a FromEuler ( Vector3 ) function.

Since you seem to be rolling your own quaternions rather than using a library, here's the conversion formula.

As a small optimization, since quaternions use half-angles, you could generate random values in the range ±15 degrees (pi/12) and feed these to the sin and cos functions directly.