External tilesets

[bertt]

Add support for external tilesets. Spec: https://github.com/CesiumGS/3d-tiles/tree/master/specification#external-tilesets

[bertt]

sample: https://github.com/CesiumGS/3d-tiles-samples/blob/master/tilesets/TilesetWithRequestVolume/tileset.json

[bertt]

Plan:

• Create/find 3d tiles for 2 cities for Cesium;
• Create tileset.json file referencing the 2 tilesets;
• Test in Cesium;
• When working, add external tilesets logic to MapBox - 3DTiles extension.

[bertt]

reduced Cesium sample of external tiles: https://bertt.github.io/cesium_external_tilesets/index_request_volume.html

In this sample, https://bertt.github.io/cesium_external_tilesets/TilesetWithRequestVolume/tileset.json references https://bertt.github.io/cesium_external_tilesets/TilesetWithRequestVolume/city/tileset.json

[bertt]

External tilesets are working in Cesium see https://bertt.github.io/cesium_external_tilesets/index.html

In MapBox-3dtiles extension some work has to be done, follow it at https://github.com/Geodan/mapbox-3dtiles/issues/22

Closing this issue.