Extensions allow the base 3D Tiles specification to be extended with new features. They may add new properties to a 3D Tiles JSON object, and may add functionality a tile format or the 3D Tiles Styling expression language.
Extensions may not remove existing properties or features, nor redefine existing properties or features to mean something else.
The optional extensions dictionary property may be added to a 3D Tiles JSON object, which contains the name of the extensions and the extension specific objects.
The following example shows a tile object with a hypothetical vendor extension which specifies a separate collision volume.
{
"transform": [
4.843178171884396, 1.2424271388626869, 0, 0,
-0.7993325488216595, 3.1159251367235608, 3.8278032889280675, 0,
0.9511533376784163, -3.7077466670407433, 3.2168186118075526, 0,
1215001.7612985559, -4736269.697480114, 4081650.708604793, 1
],
"boundingVolume": {
"box": [
0, 0, 6.701,
3.738, 0, 0,
0, 3.72, 0,
0, 0, 13.402
]
},
"geometricError": 32,
"content": {
"uri": "building.b3dm"
},
"extensions": {
"VENDOR_collision_volume": {
"box": [
0, 0, 6.8,
3.8, 0, 0,
0, 3.8, 0,
0, 0, 13.5
]
}
}
}All extensions used in a tileset or any descendant external tilesets must be listed in the tileset JSON in the top-level extensionsUsed array property, e.g.,
{
"extensionsUsed": [
"VENDOR_collision_volume"
]
}All extensions required to load and render a tileset or any descendant external tilesets must also be listed in the tileset JSON in the top-level extensionsRequired array property, such that extensionsRequired is a subset of extensionsUsed. All values in extensionsRequired must also exist in extensionsUsed.