Convert rotation in Unity Euler angles (in degrees) into 3D rotation matrix

Source: R/maths_functions.R

Converts Unity's specific (improper) Euler angles into a 3D rotation matrix for further computations.

eulunity2rot(rot_x, rot_y, rot_z)

Arguments

rot_x

Euler x angle in degrees

rot_y

Euler y angle in degrees

rot_z

Euler z angle in degrees

Value

A 3D rotation matrix in left-handed coordinates

Details

1. Unity uses (improper) Euler angles to output their internal quaternion representation. (https://docs.unity3d.com/2018.4/Documentation/Manual/QuaternionAndEulerRotationsInUnity.html)

2. These angles describe extrinsic rotations around the Z - X - Y coordinate axis (https://docs.unity3d.com/ScriptReference/Transform-eulerAngles.html)

(also verified from Unity editor and by comparing Unity output to videos)

3. The angles are given as clockwise when the axis is pointing towards the observer as the coordinate system is left-handed (verified from Unity editor)

4. The function uses basic rotation matrices and composition of rotations (e.g. https://en.wikipedia.org/wiki/Rotation_matrix#Basic_rotations, the matrices given there are for counterclockwise rotation for right-handed system; the same rotations produce clockwise rotation in left-handed system