CODEWITHSUNDEEP
three.js
nickponline
nickponline

Reputation: 25914

How do you get the axis and angle representation of a quaternion in three.js?

I have a three.js quaternion and would like to get the axis and angle representation of it. Is this possible in three.js or do I have to do this:

export function getAxisAndAngelFromQuaternion(q: Quaternion) {
  const axis = [0, 0, 0];
  const angle = 2 * Math.acos(q.w);
  if (1 - q.w * q.w < 0.000001) {
    // test to avoid divide by zero, s is always positive due to sqrt
    // if s close to zero then direction of axis not important
    axis[0] = q.x;
    axis[1] = q.y;
    axis[2] = q.z;
  } else {
    // http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToAngle/
    const s = Math.sqrt(1 - q.w * q.w);
    axis[0] = q.x / s;
    axis[1] = q.y / s;
    axis[2] = q.z / s;
  }
  return { axis: new Vector3().fromArray(axis), angle };
}

Upvotes: 0

Views: 2349

Answers (1)

dcromley
dcromley

Reputation: 1410

Is this in a pre-javascript code -- "export"? "q: Quaternion"?
Anyway, it's a relatively simple algorithm. A simplifying suggestion:

function getAxisAndAngelFromQuaternion(q) {
  const angle = 2 * Math.acos(q.w);
  var s;
  if (1 - q.w * q.w < 0.000001) {
    // test to avoid divide by zero, s is always positive due to sqrt
    // if s close to zero then direction of axis not important
    // http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToAngle/
    s = 1;
  } else { 
    s = Math.sqrt(1 - q.w * q.w);
  }
  return { axis: new Vector3(q.x/s, q.y/s, q.z/s), angle };
}

Upvotes: 4

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