For a simple example, have a look at Salvatore's answer to a GIS.SE question: https://gis.stackexchange.com/a/273464/36921 Tom ----- Buy Pie Spy: Adventures in British pastry 2010-11 on Amazon -- Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-Developer-f4099106.html