CityJSON: a compact and easy-to-use encoding of the CityGML data model

Abstract

Full details of the project: https://cityjson.orgThe international standard CityGML is both a data model and an exchange format to store digital 3D models of cities. While the data model is used by several cities, companies, and governments, in this paper we argue that its XML-based exchange format has several drawbacks. These drawbacks mean that it is difficult for developers to implement parsers for CityGML, and that practitioners have, as a consequence, to convert their data to other formats if they want to exchange them with others. We present CityJSON, a new JSON-based exchange format for the CityGML data model (version 2.0.0). CityJSON was designed with programmers in mind, so that software and APIs supporting it can be quickly built. It was also designed to be compact (a compression factor of around six with real-world datasets), and to be friendly for web and mobile development. We argue that it is considerably easier to use than the CityGML format, both for reading and for creating datasets. We discuss in this paper the main features of CityJSON, briefly present the different software packages to parse/view/edit/create files (including one to automatically convert between the JSON and GML encodings), analyse how real-world datasets compare to those of CityGML, and we also introduce Extensions, which allow us to extend the core data model in a documented manner.

The LandInfra standard and its role in solving the BIM-GIS quagmire

“…In order to avoid this last issue, we are working on two solutions: (i) a LandInfra ADE for CityGML, which will encourage the adoption of LandInfra's features, and (ii) InfraJSON, a JSON based encoding for InfraGML, which can be explored at our public GitHub repository: https:// github.com/tudelft3d/InfraJSON. Despite the precedence set by the high usage of GML (XML) in various OGC standards, GML is a bulky and cumbersome encoding that is hard to use, and thus it is often disliked by both users and developers [41,79]. By contrast, JSON provides an easy-to-use and easy-to-read alternative, such as with CityJSON 10 , which is a JSON based encoding of CityGML.…”

Harmonising the OGC Standards for the Built Environment: A CityGML Extension for LandInfra

“…Furthermore, we are working on the development of InfraJSON, a JSON (JavaScript Object Notation) based encoding for InfraGML, which can be explored at our public GitHub repository: https://github.com/tudelft3d/InfraJSON. Despite the precedence set by the high usage of GML (XML) in various OGC standards, it is a verbose and complex encoding for use in real world applications, whereas JSON provides an easy-to-use and easy-to-read alternative [46,47]. For instance, CityJSON (http://www.cityjson.org) is a JSON-based encoding for a subset of the OGC CityGML data model.…”

Requirements, Development, and Evaluation of A National Building Standard—A Swedish Case Study

“…It includes three simple datatypes (strings, numbers, booleans) and two data structures: arrays (an ordered list of elements) and objects (consisting of key/value pairs). In CityJSON, the CityGML 2.0 data model is flattened out and all hierarchies removed [28]. Figure 3 shows an example of how a building with two building parts can be represented.…”

“…Another option for a national 3D city model standard is CityJSON, a JSON implementation of a subset of the CityGML 2.0 data model. According to [62], disadvantages with CityGML are the complex and verbose GML encoding that both make it difficult to parse files and for developers to implement. In CityJSON, all hierarchies are removed, and the geometries are simplified.…”