On Thu, 9 Aug 2018 at 08:39, Nyall Dawson <nyall.daw...@gmail.com> wrote:
> On Wed, 8 Aug 2018 at 18:06, Rudi von Staden <rud...@gmail.com> wrote: > > > > > I did also calculate a range of zonal stats on the layer (which has only > one multipolygon feature), but those results were consistent between output > / memory layers. > > > > Is the area difference expected because of how shapefiles store geometry > vs how they are handled by memory layers, or could there be a bug > somewhere? Maybe this isn't the recommended way to calculate area? In case > it matters, I'm using a custom CRS: > > > > "+proj=aea +lat_1=-24 +lat_2=-32 +lat_0=0 +lon_0=24 +x_0=0 +y_0=0 > +datum=WGS84 +units=m +no_defs" > > This may be a silly question -- but can you confirm that both layers > are definitely in the same CRS? > Yes, they are both the result of an algorithm operating on the same source layer. > If so, I'd try exporting the two geometries to WKT and inspect for > differences. > There are partial differences between the WKT. It seems that the OGR layer drops some polygons. I also used isGeosValid() to check the validity, and the OGR layer reported invalid geometry, while the Memory layer was valid. I should note that the input layer has some invalid geometries (I'm using buffer by 0 to try to clean up the geometry). I've put together a test project and processing script to demonstrate the issue, including text files with the WKT of the memory and ogr features. As a side-note, the script also crashes QGIS a minute or so after running. I suspect it's because I may have used incorrect output parameters. https://www.dropbox.com/s/u1la8y63qlabiu4/area_test.zip?dl=0 Let me know if I should submit a bug report for this. Rudi
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