Hugo Ledoux

associate-prof in 3D geoinformation at TU Delft
blog contact protégés publications research slides software


I would charasterise my research as an equal mix of:

  • GIS: preparing and crunching real-world datasets so that they can be used for spatial analysis;
  • computational geometry: extending and adapting theoretical results to real-world problems;
  • implementation: I strongly believe in implementing my research results, see my open-source software page.

CityJSON: Making CityGML a useful format to exchange 3D city models

CityJSON is a format for encoding a subset of the CityGML data model (version 2.0.0) using JavaScript Object Notation (JSON). A CityJSON file represents both the geometry and the semantics of the city features of a given area, eg buildings, roads, rivers, the vegetation, and the city furniture. The aim of CityJSON is to offer an alternative to the GML encoding of CityGML, which can be verbose, complex, and thus rather frustrating to work with. CityJSON aims at being easy-to-use, both for reading datasets, and for creating them. It was designed with programmers in mind, so that tools and APIs supporting it can be quickly built.

CityJSON website

cjio: Python CLI to process and manipulate CityJSON files

Validation & automatic repair of geo-datasets

A few years ago, out of frustration at the poor quality of GIS datasets and of 3D city models I obtained, I have focussed my efforts on the validation and the automatic repair of polygons and polyhedra. This has lead to different programs that have matured enough to not be called prototypes anymore: prepair, pprepair and val3dity. I hope these will help practitioners who often spend hundreds of hours manually repairing their datasets.

Some of these are also available as web-applications.

Higher-dimensional modelling of geoinformation

The aim of the research project is to integrate the multi-dimensional characteristics of geographical data (eg space, time and scale), together in one higher-dimensional model. We develop data structures and operations to realise such a model, and we apply this model to the integration of CityGML models at different scales for instance.

Project website

GeoBIM: Bridging the gap between Geo and BIM

While there seems to be a natural integration between GIS and BIM/IFC models, the reality is rather different. The disciplines of GIS and BIM are disconnected by their modelling paradigms, software tools and open standards. Our efforts are targeted at bulding software so that one can can convert IFC to CityGML, and vice-versa.

Project website

Smart simplification of LiDAR datasets

The aim of this project, funded by the Dutch Technology Foundation STW, is to investigate algorithms to simplify LiDAR datasets. In recent years, these have considerably grown in size because of advances in acquisition technologies such as airborne laser-scanning. A vivid example is the AHN2 datasets in the Netherlands: it contains around 640 billion points (639,477,709,621 to be exact).

We reduce their size while keeping their main characteritics. While current methods often portray DSMs as 2D objects (and thus valuable information is lost), we investigate new simplification algorithms that:

  1. use 3D tools and 3D data structures, specificially the 3D medial axis transform (MAT);
  2. permit us to define 3D features—buildings, dikes, etc—and consider these while simplifying. The knowledge of the features will permit us to remove unimportant points and focus only on those of interest for a given application.

Project website

Storage, update and dissemination of massive 3D city objects

The aim of this research project, also funded by the Dutch Technology Foundation STW, is to investigate and develop methods to efficiently store and maintain 3DTOP10NL in a database, and to disseminate it to practitioners. The existing open-source database solutions for managing 3D volumetric objects are being tested with massive datasets and improved, if necessary.

The biggest challenge is the management of massive TINs (triangulated irregular networks) in a database. We investigate, design and develop new data structures, implement them, and compare different alternatives (in terms of storage space, query time, etc).

Project website

Some other research projects (some finished, some not)