OSGeo Events, FOSS4G 2008

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Using SLD definitions to display charts in a deegree WMS

Judit Mays

Building: Cape Town International Convention Centre
Room: Makuya Room (Room 1.6)
Date: 2008-09-30 01:30 PM – 03:00 PM
Last modified: 2008-09-08


The deegree framework provides, amongst others, the OGC reference implementation for Web Map Services and is capable of supporting SLD to allow for user defined style symbolization. According to OGC's SLD specification a point symbolizer referencing an external graphic needs to specify the URL to the symbol's image. References to a static image are no problem, but what happens, if you desire to display a chart which resembles the feature's properties?

A new web application has been designed for creating these dynamic chart figures. The user is able to generate charts by sending HTTP requests through the browser to a web servlet and receives images with the requested charts as a result. Chart type, appearance and data sources can all be determined using a given set of HTTP request parameters. The application can be used as standalone to display chart images for a given dataset. More interesting though, it can also be incorporated for displaying charts as symbols in a deegree WMS using SLD.

The major reason for having a special servlet rendering charts in deegree instead of using already available solutions is that it should be possible to use charts as point symbols within a map rendered by deegree WMS. The deegree WMS uses SLD for defining a layer style and so it should be possible to embed dynamically created charts without introducing deegree specific elements into an SLD document. A mechanism has been introduced to deegree that allows for accessing the properties of a feature - or rather: their values - to create a URL for referencing an external graphic within an SLD point symbolizer. The only thing you have to do to use charts as point symbols is to create an HTTP-Get call targeting the chart servlet with parameter values read from the features to be rendered.

The presentation will provide an in-depth explanation of the described mechanism and demonstrate the result in a deegree WMS.