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Alle Oberthemen / Informatik / Computergrafik / Schwerpunktkolloquium: Basic Techniques, Geometry Processing, Global Illumination
27
How are Progressive Meshes generated, stored and reconstructed? How can we do Selective Refinement?
Original mesh:
Incremental Decimation applies a series of decimation operators:

By reversing these operators, we can reconstruct from the decimated mesh


In order to make a Halfedge Collapse operator reversible, we need to store:
  • Position of the source vertex which was collapsed:
  • A pointer to the target vertex towards which was collapsed:
  • Pointers to the two boundary vertices which were adjacent to both and before the collapse:

Thus, each operator is stored as


Selective Refinement
If we want to undo an operator

the problem might be that one of the opposite vertices or does not exist:
  • / might not exist yet if it is still not expanded
  • / might not exist anymore if it has previously been split

In order to solve this problem, we store the refined mesh as a binary forest where the leaf nodes are the unrefined vertices and each inner node corresponds to a decimation operator.

During decimation, we remember from which original vertices our mesh started out. Initially, we store at every triangle corner a pointer to the incident vertex. As we decimate the mesh, these triangle corner labels remain intact. When we store an operator, instead of storing , as the vertices in the decimated mesh, we store the values stored in the respective triangle corners.

If we want to refine at a vertex , we find the two opposite vertices , in the currently refined mesh by walking up the binary forest of operators until we find vertices that have already been instantiated.
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Karteninfo:
Autor: janisborn
Oberthema: Informatik
Thema: Computergrafik
Schule / Uni: RWTH Aachen
Ort: Aachen
Veröffentlicht: 18.05.2022

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