Free and Open Source Software for Geomatics Conference FOSS4G 2010 Barcelona

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Urban management services are increasingly in need of 3D models for their cities. The OGC standard corresponding to this need of 3D city modeling is CityGML.

As far as OpenSource solutions are concerned, available and classic spatial data architectures and softwares are still mainly 2-dimensional.

This presentation will give some insight into recent steps achieved in storing volumes inside PostGIS, that is to say, PolyhedralSurfaces support.

Various aspect of the problem will be covered, beginning with OGC SFS and ISO SQL/MM standards regarding the issue.

Then LOD will be explained, emphasizing the fact that different CityGML levels of detail can be kept in database for a same feature. According to this standard, LOD1 is the simplest 3D Level Of Detail, with features genereralized as 3D boxes, whereas LOD4 needs enough details to navigate inside a building.

Validations and integrity verifications are two important points for 3D geometric volumes, and correspond to ST_IsValid and ST_IsValidReason PostGIS functions. Manipulation functions are also part of the implementation plan : volume computation, centroid location, and other functions with specific 3D algorithms.

Some primitives are also deeply needed to deal with import and export, like ST_AsX3D, ST_AsCollada functions… Finally, the texture issue will be also explained, as it is strongly needed for any CityGML LOD 2 rendering (and upper levels too).

Once 3D features are stored inside PostGIS, they could be exposed through Web Services such as W3DS or WFS, enabling full OpenSource solutions for 3D city exploration.

Further planned steps are 3D topological functions, like ST_Intersects or ST_Contains with real 3D operators.



Olivier Courtin - Oslandia


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