How can I convert Euler to Local and Local to Euler?
Before convert : // Euler
[ x: -54.9770929, y: -39.3148223, z: -21.0580199 ]
After Convert : // Local
[ -45, -45, 0 ]
I’m afraid this question does not make sense. Euler angles can be used in order to describe the orientation of a 3D object with respect to a fixed coordinate system. Alternatives for Euler angles are quaternions or rotation matrices.
The term Local refers to a coordinate space. You use transformation matrices in order to convert from one space to an other. For example local coordinates (object space) are transformed with the modelView matrix to eye coordinates (eye space).
More information about transformations in OpenGL/WebGL: http://www.songho.ca/opengl/gl_transform.html