Specify the JSON structure

[javagl]

The quantized mesh representation relies on a layer.json file that is mentioned in the README, but there is virtually no information about what this file actually is.

There was a thread in the forum which contained an example and a very basic description of the contents. (Some further internal discussion revolved around the role of availability, but that seems to be a broader topic). Essentially, people seem to reverse engineer the CesiumTerrainProvider.js to find out what this JSON may contain. Doing a websearch for "layer.json" cesium makes clear that people are struggling with this file in many ways. From what I've found until now, the layer.json seems to be a subset of the tilejson format, but it's not clear which parts of this are actually supported.

In any case: If it is a tilejson file, then this should be mentioned in the README - in doubt, with a tilejson version number, or details about which parts of tilejson are actually understood by the CesiumTerrainProvider.