Streaming CityJSON datasets

TL;DR

CityJSONSeq is a new streaming format for large 3D city models based on JSON Text Sequences, offering improved compression, processing speed, and memory efficiency over traditional CityJSON.

Contribution

The paper introduces CityJSONSeq, a novel streaming format for CityJSON datasets, with open-source tools and analysis of its advantages over CityJSON.

Findings

CityJSONSeq is about 10% more compact than CityJSON.

Processing time is reduced by an order of magnitude.

Memory usage is significantly lower with CityJSONSeq.

Abstract

We introduce CityJSON Text Sequences (CityJSONSeq in short), a format based on JSON Text Sequences and CityJSON. CityJSONSeq was added to the CityJSON version 2.0 standard to allow us to stream very large 3D city models. The main idea is to decompose a CityJSON dataset into its individual city objects (each building, each tree, etc.) and create several independent JSON objects of a newly defined type: 'CityJSONFeature'. We elaborate on the engineering decisions that were taken to develop CityJSONSeq, we present the open-source software we have developed to convert to and from CityJSONSeq, and we discuss different aspects of the new format, eg filesize, usability, memory footprint, etc. For several use-cases, we consider CityJSONSeq to be a better format than CityJSON because: (1) once serialised it is about 10% more compact; (2) it takes an order of magnitude less time to process; and (3) it uses significantly less memory.