This document describes a variant of the frustum grid that uses spherical depth shells instead of planar depth slices, while retaining the standard perspective lateral coordinates.
The planar frustum grid uses a piecewise depth distribution. Key parameters:
- κ = 2·tan(θ/2)/N — pixel cone slope (θ = FOV, N = pixels along one axis)
- s — voxel size (world-space units)
