Cross field singularity index violates Poincaré-Hopf theorem #2526
Description
Describe the bug
The singularity index computed via igl::find_cross_field_singularities is always positive, which leads to the violation of Poincaré-Hopf theorem (section 3.2 of [1]).
The original discussion and unit tests is from libigl/libigl-python-bindings#295
Platform
- Windows
- macOS
- Linux
[1] Vaxman, Amir, et al. "Directional field synthesis, design, and processing." Computer graphics forum. Vol. 35. No. 2. 2016.