Media types

[cportele]

The current rules for media types have at least two problems:

• application/json+i3s and application/json+3dtiles are not registered media types and thus cannot be used. As an aside, if they would be registered, the pattern should be "xxx+json" to conform to the IANA rules for JSON media types.
• application/json+3dtiles violates the 3D Tiles specification which explicitly states that tileset files use ... the application/json media type.

Use the correct, registered media types for the different formats.

[jerstlouis]

Outcome of discussion at session in 127th members meeting in Singapore:
For the i3s BVH, we can use what Esri already uses which is:

application/vnd.esri.i3s.json+gzip

where the JSON files are also always pre-gzip-compressed.
Esri or OGC should register this media type with IANA.

For 3D Tiles, the correct order would have been application/3dtiles+json, rather than the other way around. However, the 3D Tiles spec currently explicitly states that application/json should be used.

@lilleyse would Cesium like to register application/3dtiles+json and update this in a later version of the spec, in which case in OGC API - 3D GeoVolumes we could adopt this option (I think this would be preferable from an OGC perspective, to avoid confusion with other potential JSON BVH), or should we just stick to the generic application/json currently mandated in the spec (given that i3s would now use a different media type to differentiate it)? Thanks.

Action: Update i3s media type in draft to application/vnd.esri.i3s.json+gzip

Action: OGC or Esri to register application/vnd.esri.i3s.json+gzip with IANA

Action: Update 3D Tiles media type in draft to application/json or application/3dtiles+json based on feedback from Cesium

Action?: OGC or Cesium to register application/3dtiles+json with IANA

[lilleyse]

We plan on registering media types for various file formats in 3D Tiles, but it likely won't happen until the next spec revision. application/3dtiles+json seems like the right choice in the future but for now I would stick with application/json.

CC CesiumGS/3d-tiles#341