On Fri, 19 Jul 2019 at 23:15, Andreas Neumann <a.neum...@carto.net> wrote:
> For myself, I decided to never make fun again about other people not > understanding projections, given that I make such mistakes myself ... I had this moment of realisation too while reading through https://lists.osgeo.org/pipermail/proj/2019-July/008703.html and https://www.openstreetmap.org/user/StephaneP/diary/390290 (all those "spatial isn't special" proponents trying to do data science on raw x/y alone are about to have a ten ton weight dropped on their heads) Nyall > > I wonder if it would make sense to issue a warning if a user creates data > outside of the valid bounds of a projection? It would definitely make sense > for stupid people like myself ... > > Thanks and greetings, > > Andreas > > On 2019-07-19 01:18, Nyall Dawson wrote: > > On Fri, 19 Jul 2019 at 00:38, Andreas Neumann <a.neum...@carto.net> wrote: > > > Hi, > > We are having issues on the QGIS 3.4 release that the difference between and > ellipsoidical and planimetric distance (and area) is huge. Too huge. > > We have this issue on Windows 3.4.9, but on Linux (a bit newer commit) I > don't have the same huge difference, but rather a very reasonable one. > > I noticed that while the Windows version was built with proj 520 and the > Linux version with 493, so a bit older. > > But I don't know if the measurement tool in QGIS is using proj at all or not? > If yes, could it be that newer proj releases made things worse regarding > ellipsoidical measurements? > > > It's possible. The actual measurement calculation uses code ported > from GRASS (and not the proj implementation of these algorithms), but > proj IS used in transforming map/measure coordinates prior to > calculating the distance. Possibly something has changed there which > is impacting this. > > Could you please test: > > 1. Do you see the same distance values when measuring feature lengths? > I.e. setup a layer with a feature with the same line as you are > measuring, and check the identify tool derived attributes or $length > value for it. > > 2. Can you confirm that the project ellipsoid settings are identical > between the windows & linux builds? > > 3. Can you share an example I can test with? > > Nyall > > _______________________________________________ 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
