Vector data... in glTF?

[lilleyse]

This is an idea I've been playing around with for a while. Can we use glTF for vector data? Specifically, large amounts of 3D cartesian vector data. Here are some initial ideas.

Points

• Use primitive mode: 0 (POINTS)
• Use EXT_mesh_features and EXT_structural_metadata to associate points with metadata
  • Feature ID by Index + property tables
• Styling is applied separately, e.g. with 3D Tiles Declarative Styling
  • This would include label rendering, anchor lines, etc.

Note

• How does this relate to KHR_billboard?

Lines

• Use primitive mode: 1 (LINES), mode: 2 (LINE_LOOP) or mode: 3 (LINE_STRIP)
  • For the latter two, use EXT_mesh_primitive_restart to batch multiple lines into a single primitive
• Use EXT_mesh_features and EXT_structural_metadata to associate lines with metadata.
  • Feature ID by Vertex + property tables.
• Styling is applied separately, e.g. with 3D Tiles Declarative Styling
  • This would include mitering, line width, dashed patterns, etc.

Polygons

• Use primitive mode: 4 (TRIANGLES) - polygons are pre-triangulated for performance reasons
• Use EXT_mesh_features and EXT_structural_metadata to associate polygons with metadata.
  • Feature ID by Vertex + property tables.
• Indicate which edges form the outline
  • Evaluate EXT_mesh_primitive_edge_visibility
• Styling is applied separately, e.g. with 3D Tiles Declarative Styling
  • This would include outline, fill pattern, etc.

Styling

• Styling features would happen client side. Some examples:
  • Points: labels, anchor lines, etc
  • Lines: mitering, line width, dashed patterns, etc
  • Polygons: outline, fill pattern, etc
• Styling would also define layering, ordering, and draping behavior
• 3D Tiles Declarative Styling files could be provided alongside a tileset.json

Compression

• From previous experiments, glTF + meshopt + gzip file size was on par with the legacy .vctr format + gzip
• Haven't compared against other formats like Mapbox Vector Tiles, MapLibre Tiles, or Geobuf

Demo

Here's a demo of some vector data (provided by Maxar) converted from GeoJSON to 3D Tiles - includes line and polygon features and runtime styling. No new extensions and running in stock CesiumJS.

glTF files are using the following extensions:

• EXT_mesh_features
• EXT_structural_metadata
• EXT_meshopt_compression