An overview of the GNOSIS Map Tiles (GMTs) open specifications for tiling geospatial data developed by Ecere in conjunction with OGC Testbed 13 and 14 and the latest draft specifications can be found in OGC Engineering Report:
http://docs.opengeospatial.org/per/18-025.html#GMTSpecs
GMTs can contain different types of data such as vector data, satellite imagery, coverages/elevation models, point clouds and either embedded or referenced 3D models (e.g. using Ecere's E3D format, or another encoding such as glTF for example).
GMTs are compact, ensure proper vector topology, and minimizes the time required to load onto GPU for hardware accelerated rendering.