Technologies for rendering and interacting with 3D content on the web have been in the development for centuries and are readily available on modern browsers, including mobile browsers on smartphones. Currently, WebGL 2 is the state-of-the-art technology for 3D in browsers.
3D city- and Building Information Modeling (BIM)-viewers are using modern WebGL and JavaScript technologies to provide viewing functionality of detailed geospatial and building design data on any desktop or mobile browser, without the need to install additional software or browser plugins. The 3D city viewer used by the CHEK Project, VC Map (https://github.com/virtualcitySYSTEMS/map-ui ) developed by Virtual City Systems, is built upon OpenLayers (https://openlayers.org/ ) and CesiumJS (https://cesium.com/ ) on the rendering level, for visualizing 2D and 3D geo-data, respectively. JavaScript based mapping libraries facilitate the dissemination of dynamic maps on the web.
For streaming 3D content within these web apps, a wide range of proprietary and open formats are available. Currently, the most widely adopted format is glTF developed by KHRONOS Group. “glTF™ is a royalty-free specification for the efficient transmission and loading of 3D scenes and models by engines and applications” https://www.khronos.org/gltf/). Software providers rely on glTF due to its efficiency and ubiquitous support in software libraries. glTF is suitable for visualizing 3D models of individual buildings on the web. They can be structured in a way that supports the Digital Building Permit (DBP) process by organizing entities into topics, such as construction elements, electrical systems, pipes, outer installations, and so on. These assets can be extracted using AEC software.
On the other hand, analysis on a smaller scale, such as vicinity checks, are conducted in geospatial systems that require a different streaming approach. The open standard “3D Tiles”, which has been developed on top of glTF is suited for streaming entire 3D city models. It has been adopted by the Open Geospatial Consortium. “3D Tiles is designed for streaming and rendering massive 3D geospatial content such as Photogrammetry, 3D Buildings, BIM/CAD, Instanced Features, and Point Clouds” (https://www.ogc.org/standard/3dtiles/). The main advantage over using plain architectural models or model assemblies is that the complexity of building structures can be maintained without sacrificing rendering performance, which is crucial when displaying a huge urban environment. Semantic elements such as individual wall faces or construction parts can be still identified and queried, therefore allowing automated checks based on geometrical properties.
In the EU, 3D city models maintained by municipalities for city planning and other purposes are encouraged to be modelled as CityGML data sets and stored in specialized databases. CityGML is a storage container and not suitable for developing efficient web applications. Thus, additional software tools are needed for converting CityGML content to web-ready streaming formats. To achieve maximum interoperability, open streaming APIs such as 3D Tiles are used to implement this approach, and combined with geospatial service APIs that are commonly provided by data portals of municipalities.
Geospatial service APIs are commonly defined by the OGC and adopted by municipalities and spatial data infrastructure initiatives such as INSPIRE. Well defined APIs are available for sharing raw vector data, rendered maps or any kind, orthophotos or satellite imagery, raster data (e.g. terrain data), and for making meta data available as catalogues. These APIs are defined as REST web interfaces and can be combined and nested in a flexible manner for creating more sophisticated applications.
The most common OGC services are Web coverage services (WCS) (https://www.ogc.org/standard/wcs/ ), web map services (WMS) (https://www.ogc.org/standard/wms/ ), web map tile services (WMTS) (https://www.ogc.org/standard/wmts/ ) and web feature services (WFS) (https://www.ogc.org/standard/wfs/ ). These are often utilised to disseminate urban development plans and zoning maps. The appropriate interface is chosen depending on the respective task. This results in a range of possibilities, from merely querying map images and associated feature information of zoning plans to deriving volumetric models of permitted building spaces based on information such as maximum allowed construction heights and minimum distances by exchanging information at feature level. The overlay of spatial regulations defined by municipalities and building designs provided by architects can only be achieved using open web interfaces.
Cloud-based platforms are being developed as collaboration tool for BIM in the construction and architecture industry to facilitate the sharing, collaboration, and management of BIM models and data among architects, engineers, contractors, and other stakeholders involved in construction projects. Interoperability with AEC software is achieved by supporting various BIM file formats and standards, allowing users to import and export models in formats like IFC (Industry Foundation Classes). In the context of DBP, a web frontend can be used by project owners as well as municipality workers. To support this use case, 3D assets are converted to glTF for realistic viewing and evaluating compliance with local regulations. To integrate 3D city viewers and BIM collaboration platforms, REST APIs can be used for accessing backend functionality of the BIM platform, such as querying projects, retrieving assets such as BIM models with its raw CAD and derived visualization data, from the 3D city viewer. Or vice versa, the map interface enables querying city data and associated apps for visualization, as well as triggering vicinity checking and querying results from the city viewer from the BIM platform. This allows for inspection and analysis of building designs in an urban context.
--tbc by CYPE about the open API —