Don't know if any of the links in this reply from Nyall are of any use? https://lists.osgeo.org/pipermail/qgis-developer/2018-September/054480.html 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