GS Kernel size & opacity compensation

[CedricGuillemet]

kernel Size to simulate point spread function (default 0.3).

BABYLON.GaussianSplattingMaterial.KernelSize = 0.1;

autonomousvision/mip-splatting#18 (comment)

Compensation

BABYLON.GaussianSplattingMaterial.Compensation = true;

nerfstudio-project/gsplat#117

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