Write linear-space SCALE in GLB export to follow KHR_gaussian_splatting spec#268
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…ng spec The KHR_gaussian_splatting spec requires KHR_gaussian_splatting:SCALE to be linear and non-negative, but the GLB writer stored the raw log-space scale values (the internal/PLY convention). Spec-conformant viewers therefore failed to visualize the exported splats. Apply Math.exp() to the scale components on export, mirroring the sigmoid activation already applied to opacity. exp() is always positive, so the non-negative requirement holds by construction. This matches how scale is interpreted elsewhere (the AABB/renderer path exponentiates the stored log-space scale). Add a regression test that parses the exported GLB and asserts SCALE equals exp(input) and OPACITY equals sigmoid(input). Fixes #267. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
GLB export wrote
KHR_gaussian_splatting:SCALEin log-space, but the KHR_gaussian_splatting spec requires scale to be linear and non-negative:As a result, viewers that conform to the spec fail to visualize the exported splats. Opacity was already handled correctly (sigmoid activation); scale was simply missing its
exp()activation.Fix
Apply
Math.exp()to each scale component in the GLB writer, mirroring the sigmoid already applied to opacity.exp()is always positive, so the non-negative requirement is satisfied by construction.This matches how scale is interpreted elsewhere in the codebase — e.g. the AABB/renderer path exponentiates the stored log-space scale (
Math.exp(...)), and the coordinate-space transform addsMath.log(s)for a uniform scale.Test
Adds
test/write-glb.test.mjs, which writes a GLB from a table with known log-space scales and logit opacities, parses the binary back, and asserts:KHR_gaussian_splatting:SCALEequalsexp(input)and is non-negativeKHR_gaussian_splatting:OPACITYequalssigmoid(input)and lies in[0, 1]Fixes #267.