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leaflet-sparql

This web page consists of a very basic Leaflet webmap that displays the results of a Sparql query on a Virtuoso endpoint.

It depends on Leaflet (webmapping library), jQuery (general javascript framework) and jQueryGeo (geometry processing library).

It is thought as a base for a more complex web map (multiple/custom queries, editing capabilities, ...).

Demo : http://128.178.21.39:8080/map/

Notes about Virtuoso

Unlike Strabon, Virtuoso doesn't implement the standard GeoSparql defined by OGC. This means that the Sparql query must be rewritten if the endpoint is not a Virtuoso endpoint.

Unlike Strabon, Virtuoso is unable to serve directly well-formatted GeoJSON to be displayed with leaflet. The following formatting is done to transform Virtuoso's Json response to standard GeoJSON's responses :

  • restructure the Json object
  • convert the geographical representation from WKT to GeoJSON

This means that that part of the javascript could be dropped if using Strabon.

By default, Virtuoso doesn't allow CORS (cross-origin requests), which makes it impossible to dynamically load data from Javascript (the error looks like "No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access."). See http://virtuoso.openlinksw.com/dataspace/doc/dav/wiki/Main/VirtTipsAndTricksCORsEnableSPARQLURLs to solve this.