Thanks for your answer Andreas, I've one question though: If the data source is a Shapefile and simplification is enabled, will the Field Calculator results be dependent on the zoom? I expect they will be. Isn't that a big source of potential confusion for the users? And yes, I do understand that the problem is more complicated/different when server-side simplification is performed. Best wishes, Anita
On Sun, Jun 22, 2014 at 4:46 PM, Andreas Neumann <a.neum...@carto.net> wrote: > Hi Anita, > > While I agree with you in general the difficulty is that if you do > serverside simplification QGIS does not even see the original geometry > anymore. So not easy to solve. > > On the other hand you have several relatively easy workarounds. Either: > > - disable simplification > - write the area to a new column > - calculate area in the database (e.g. Postgis, Spatialite) > > Using $area in symbology isn't too efficient anyway. For each zoom and > pan you will calculate the same areas again and again. > > Sorry that I can't give any better answers - just the recommendation > that you should not calculate areas on-the-fly for symbology purposes. > > Andreas > > > Am 22.06.2014 13:59, schrieb Anita Graser: >> Hi, >> I noticed this issue because I had a choropleth map showing population >> density (calculated dynamically using "population"/$area). Some of the >> polygons changed color when zooming. Simplify geometry, which is >> active by default, caused minor changes to the value of $area when >> zooming. I think $area should always be calculated from the original >> geometry rather than the simplifies one to avoid such issues. >> Is this a known problem, or should I open a ticket? >> Best wishes, >> Anita >> _______________________________________________ >> Qgis-developer mailing list >> Qgis-developer@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/qgis-developer >> > > _______________________________________________ > Qgis-developer mailing list > Qgis-developer@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer