On mercredi 29 août 2018 21:50:25 CEST Andreas Neumann wrote: > Hi Even, > > Thank you very much for the detailed analysis of the spatial filter > issue we have here, that causes the disappearing grid lines. > > Would you be interested to work on fixing this issue on our bug fixing > program? This problem annoyed me for quite some time. And it appears on > different world projections.
I might have a look at this, if nobody else more familiar with the relevant code looks at it. Is there a ticket filed about that ? Even > > Thanks, > > Andreas > > Am 28.08.2018 um 22:19 schrieb Even Rouault: > > Yes, seems restricted to reprojection cases > > > > This seems to be an issue with the spatial filter issued to OGR > > > > At the zooms where the lines disappear, there are requests like: > > > > Thread 23 "Thread (pooled)" hit Breakpoint 2, OGR_L_SetSpatialFilterRect > > (hLayer=0x7f81180c90a0, dfMinX=-179.79163612932865, > > dfMinY=-69.446164378986353, dfMaxX=179.90530755284408, > > dfMaxY=78.959077253477474) at ogrlayer.cpp:1223 > > > > At the zooms where that work (even when zoomed in), there are like: > > > > Thread 29 "Thread (pooled)" hit Breakpoint 2, OGR_L_SetSpatialFilterRect > > (hLayer=0x7f81180c90a0, dfMinX=-180, dfMinY=-90, dfMaxX=180, dfMaxY=90) at > > ogrlayer.cpp:1223 > > > > > > I haven't looked at the QGIS code that computes this bounding box, but > > from my experience with gdalwarp which has similar challenges, it is > > tricky to compute a source bounding box from a target bounding box, > > because sometimes the coordinates in the target bounding box do not > > correspond to a physical point on Eath, and hence inverse projection > > fails. So you have to resort to a grid sampling approach, but that makes > > you miss the exact boundaries. So probably that a band-aid fix would be > > to add some ad-hoc logic, like "if the source SRS is long/lat, and the > > computed extent is almost worldwide, then extend it to full worlwide (or > > do not emit a spatial filter at all)" > > > > Even > > > >> With EPSG:4326 it does not seem to happen, but I tried EPSG:3857 and the > >> -180,180 grid lines do appear and disappear at different zoom levels. I > >> also confirm this with the Robinson projection with the addition that the > >> -90, 90 degree latitude lines also appear and disappear. > >> > >> Calvin > >> > >> On Tue, Aug 28, 2018 at 3:31 PM, Andreas Neumann <a.neum...@carto.net> > >> > >> wrote: > >>> Hi again, > >>> > >>> For some time already I noticed that, depending on the zoom level, the > >>> -180 / 180 degree grid lines appear / disappear in QGIS. This is > >>> unrelated > >>> to the EqualEarth projection just discussed and also appears on other > >>> world > >>> projections, like the Robinson projection. > >>> > >>> Here is the testfile I used with world (countries) and gridlines: > >>> http://www.carto.net/neumann/temp/gridlines.gpkg > >>> > >>> Can you reproduce this behaviour? > >>> > >>> Any idea why this happens and how this could be fixed? > >>> > >>> Thanks, > >>> > >>> Andreas > >>> > >>> > >>> _______________________________________________ > >>> QGIS-Developer mailing list > >>> QGIS-Developer@lists.osgeo.org > >>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > >>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
