Function estimate_plane_covariances_grid_gpu 

pub fn estimate_plane_covariances_grid_gpu(
    runtime: &WgpuRuntime,
    x: &[f32],
    y: &[f32],
    z: &[f32],
    radius: f32,
    epsilon: f32,
) -> SpatialResult<Vec<GpuCovariance>>

Estimates per-point plane-regularized covariances on the GPU via a uniform grid radius neighbor search.

Returns one GpuCovariance per point — the unique elements of a covariance matrix whose eigenvalues have been set to (epsilon, 1, 1) (the GICP plane-to-plane model). Grid construction (counting sort) runs on the CPU; the neighbor gather, covariance, and eigen-decomposition run on the GPU.