Ask HN: How does choice of coordinate system affect 3D transformation?

2 shivajikobardan 2 8/26/2025, 7:30:35 AM
I am going through rotation about an arbitrary axis in three dimensions, rotation about x, y and z-axes in three dimensions etc.

And there are coordinate system that are called as:

- left handed coordinate system

- right handed coordinate system

For some reasons I have observed ambiguousness in various rotation matrices.

Example: Rotation about y-axis by t could be written as:

    $$
    \begin{bmatrix}
    cost & 0 & -sint & 0 \\
    0 & 1 & 0 & 0 \\
    sint & 0 & cost & 0 \\
    0 & 0 & 0 & 1
    \end{bmatrix}
    $$
    
I have seen someone interchanging the sin of sint in some textbooks/authors/videos(like this: https://www.youtube.com/watch?v=ZEXpxIwpGbY)

Check 25:28 of the video and step numbered (3).

This is frying my brain since few days. I know getting free assistance in this huge topic is not possible. But even if you could display a small support, small guidance, that would be greatly push me through this phase.

References:

https://stackoverflow.com/questions/19747082/how-does-coordinate-system-handedness-relate-to-rotation-direction-and-vertices

Comments (2)

shivajikobardan · 4h ago
My question about sign swapping is explained by this blog

https://www.cairographics.org/cookbook/matrix_conventions/

The reason behind this is called pre-multiplication vs post-multiplication technique of matrix transformation.

Post-multiplication

- transformation matrix appears after the position vector matrix

- position vector matrix in homogenous coordinates is represented as a row matrix.

Pre-multiplication

- transformation matrix appears before the position vector matrix

- here the position vectors in homogenous coordinates are represented in column matrix.

Textbook reference: Mathematical elements for computer graphics Rogers/Adams

shivajikobardan · 3h ago
About finding angles, found some good information(I have not yet understood).

https://www.math.umd.edu/~wmg/Marsh.pdf