UniVRM Coordinate Transformations
Mon, Apr 16, 2018
UniVRM automatically performs the coordinate transformation with GLTF during import / export.
VRM coordinate system
Since VRM is an extension of GLTF, it conforms to the coordinate system of GLTF. It is right-handed Y-UP (OpenGL standard) coordinate system.
- Right: X+
- Up: Y+
- In front: Z-
Unity coordinate system
Left-handed Y-UP coordinate system。
- Right:X+
- Up:Y+
- In front:Z+ (+- is inverted)
Transformation matrix
Z-axis is inverted.
Vector3 (Position, Normal, etc.)
public static Vector3 ReverseZ(this Vector3 v)
{
return new Vector3(v.x, v.y, -v.z);
}Quaternion (Rotation)
public static Quaternion ReverseZ(this Quaternion q)
{
float angle;
Vector3 axis;
q.ToAngleAxis(out angle, out axis);
return Quaternion.AngleAxis(-angle, ReverseZ(axis));
}Matrix (BindMatrices)
Not working well if a scale value is contained.
public static Matrix4x4 ReverseZ(this Matrix4x4 m)
{
#if UNITY_2017_1_OR_NEWER
m.SetTRS(m.GetColumn(3).ReverseZ(), m.rotation.ReverseZ(), Vector3.one);
#else
m.SetTRS(m.ExtractPosition().ReverseZ(), m.ExtractRotation().ReverseZ(), Vector3.one);
#endif
return m;
}