National-scale 3D city model datasets are expanding rapidly -- Japan's PLATEAU project alone publishes over 170,000 files, and the Netherlands' 3DBAG covers all approximately 11 million buildings in the country -- yet no standardised mechanism exists for discovering and cataloguing these datasets across repositories.
Essential properties such as coordinate reference systems, levels of detail (LoDs), and types of city objects remain embedded inside data files in a variety of formats (for example, CityGML, CityJSON, or FlatCityBuf), making them invisible to search engines and catalogue services.
We will present and discuss three contributions we have made to address that gap:
- The STAC 3D City Models Extension, a formal extension to the SpatioTemporal Asset Catalog (STAC) specification that adds metadata fields for LoDs, city object types, semantic surfaces, textures, materials, and attribute schemas.
- The software
city3dstac, an open-source command-line tool written in Rust that automatically extracts metadata from 3D city models in multiple formats and generates STAC-compliant metadata. <> - A prototype registry that currently indexes several STAC Collections around the world. It already includes the national-scale 3D BAG, American Cities, and Estonia datasets, PLATEAU, and more are being added.
Existing STAC clients can browse the catalogue without modification, demonstrating that 3D city model metadata integrates directly into the broader geospatial data infrastructure.