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Use of SLD standard by the ELF project

dominique laurent, Thomas Ellet, Anja Hopfstock and Marian de Vries

(Submission #241)


The European Location Framework (ELF) project aims to provide harmonised, INSPIRE-based data from NMCAs. Based on this harmonised data, ELF has designed several view products using SLD standard, namely the Administrative BaseMap, the Topographic BaseMap and the Cadastral Index Map. In addition, ELF has transformed the INSPIRE documentation about portrayal into operational Style Layer Descriptor (SLD) files. The SLD standard is composed of two parts: the filter that defines the feature type and selection criteria to be used in the layer and the portrayal rules themselves (symbol, applicable scales, positioning rules for labels). When designing a view product, the first phase is obviously to design the SLD file. First difficulty was the complex data model of some INSPIRE themes (especially Transport Network), considered as not convenient for the selection criteria aiming to define the layers: choice was made to use simplified models derived from the INSPIRE. Then, it should be decided how to design the SLD file; e.g. for the Administrative BaseMap, the selection criteria and portrayal rules were elaborated using QGIS and then exported as SLD but some manual work remained to deal with the labels. The ELF project has developed an SLD editor tool that facilitates the modification of existing SLD files- regarding the portrayal rules. The second phase is the use of SLD when implementing view services. In general, the SLD standard has been a very useful tool in the ELF context, especially for the view products using a decentralised production process: the Topographic BaseMap and the Cadastral Index Map are based on national WMS set up by various NMCAs using different implementation solutions, such as Map Server, GeoServer, ArcGIS server, Intergraph WebMapServer. Globally, the use of SLD standard has enabled data providers to get (relatively) homogeneous rendering in a multiple actors, multiple tools -and multiple versions context. However, some difficulties remain: for instance, the SLD file has to be adapted for some implementation solutions, e.g. to be transformed into MapFiles for Map Server. In addition, it is difficult to fully specify the label process within the SLD and significant part of the work is up to the implementation solution. In conclusion, the SLD standard has really empowered ELF to design its view products; it has proved to be good enough regarding the (simple) symbols to be applied to features but there remain some progress to be done regarding the label process.


Topic Area:  [2.9] Challenges and approaches to standardization of data and interoperability of systems.
Abstract Type:  Oral Presentation

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