Exact camera rotation matrix and rotation order used by RealityCapture

Development Pipeline & Plugins
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1

Hi everyone,

I’m trying to visualize RealityCapture camera poses in my own tool (Three.js) and I’d like to match RealityCapture’s camera orientation exactly.

For that, I need to know the exact form of the rotation matrix that RealityCapture uses, expressed explicitly with cos/sin of the three angles, and also the rotation order (which axis is rotated first, second, third).

Concretely, my questions are:

  1. Which rotation order does RealityCapture use for its three angles?

  2. What is the explicit 3×3 rotation matrix in terms of the three angles?
    For example, in the style:

    R = [ r11 r12 r13
      r21 r22 r23
      r31 r32 r33 ]

r11 = cos(φ)*cos(κ) + ...
r12 = ...
...

    I’d like to know the exact formulas RealityCapture uses internally (with sin/cos of the angles), so I can reproduce them 1:1.

  3. Are these angles interpreted as rotations that map:

    • from world to camera coordinates, or

    • from camera to world coordinates?

    (i.e. is the exported rotation matrix R such that X_cam = R * X_world or the other way around?)

I’m not looking for a general Euler-angles explanation, but specifically for the RealityCapture definition: rotation order and the precise matrix entries.

If someone from the RC team or anyone who has already reverse-engineered/verified this could post the exact formulas, that would be super helpful.

Thanks in advance!

2

You can check this post about it: Importing camera alignment in THREE.JS

It looks like there is some answer in the link from the first comment.

There you can find also some additional information: Camera Parameters in the output XMP file