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CesiumGS / gltf-pipeline

Content pipeline tools for optimizing glTF assets. :globe_with_meridians:

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Output glb contains more vertex (+48%) with draco compression.

ketourneau opened this issue · comments

commented

Hi,

We convert this glb file with gltf-pipeline -i file.glb -o output.glb -b -d
And we got problem, output glb contains more vertex (+48%) than input glb.

Input glb => 7 932 745 vertex
Output glb => 11 744 221 vertex

Does anyone have an explanation ?

commented

We found answer: google/draco#71

Another explanation (p15) : https://tuprints.ulb.tu-darmstadt.de/14189/1/vonBuelow-2017-BA.pdf

Draco supports compressing vertex positions, colors, normals and texture coordinates but cannot encode non-manifold meshes without losing adjacency information. The loss of adjacency information is due to the inability of the used Edgebreaker algorithm to encode non-manifold meshes. To fix this issue, Draco copies vertices and its attributes on every non-manifold edge or vertex to ensure a 2-manifold mesh.