The docs specify that “3D Tiles uses a right-handed Cartesian coordinate system”, and tile transform matrices are affine. CRS is specified only as the global coordinate system at the tileset level. My question is whether saying the coordinates are cartesian specifically only refers to the local coordinates, rather than the global coordinates that would result when applying a CRS projection (which in general is going to be nonlinear). For example, in rendering, the global cartesian coordinates needed would be derived by taking the local gltf ones, multiplying by the hierarchy of parent tile transforms, and finally applying the CRS projection (which is not in general just an affine transform since it accounts for curvature)—is this correct?
3D Tiles doesn’t have CRS projections, it’s always cartesian, whether that’s a local cartesian coordinate system or a global cartesian coordinate system like EPSG:4978 (ECEF).
The tiling pipeline is responsible for converting the source data from its original projection to global cartesian coordinates.
There are some nuances when it comes to voxels since we support an ellipsoid shape type, where data is gridded in spherical coordinates.