On 05/03/18 12:12, Idan Miara wrote: > Forgive me for not understanding the fine details of the flaws in Web > Mercator. > Fast forward back the reality where many tile servers provide tiles in > 3857, and 4326 to 3857 seems OK, how can I debug this issue in the > inverse transformation?
I don't think you can. The "fix" would be to force QGIS to treat all data as WGS:4326 (see again the link I provided in my first answer). That seems to be the reality of this mess. Best, Ben > > I guess I could export the OSM map in 3857 to TIF to rule out the > possibility that the problem in the tile server, so that I can be sure > that QGIS is transforming the raster? > > > On 5 Mar 2018 12:57, "Benjamin Ducke" <[email protected] > <mailto:[email protected]>> wrote: > > It all boils down to the same fundamental issue: > Google Earth/Maps, etc. _pretend_ that their data > is WGS84, but they do not implement the WGS84 > ellipsoid. So when tools like PROJ attempt to > do the _technically correct_ thing and perform > a datum transformation WGS84 <-> Web Mercator, then > data ends up in the wrong place. If they don't, > then people get confused, because the two systems > are different. This confusion is now seeping into > PROJ and from there into higher-level apps like > QGIS. I wish EPSG had never included Web Mercator into > its database. Then we could just ignore all of this, > use EPSG:4326 and live in blissful ignorance. > > On 05/03/18 11:42, Idan Miara wrote: > > Thanks for you reply, > > Since the problem exist also in 2.18 I don't think it is related with > > PROJ 5.0, Right? > > > > On 5 Mar 2018 12:39, "Kristian Evers" <[email protected] > <mailto:[email protected]> > > <mailto:[email protected] <mailto:[email protected]>>> wrote: > > > > If you are using PROJ 5.0.0 it is likely to be caused by this > known > > issue: > > > > https://github.com/OSGeo/proj.4/issues/834 > <https://github.com/OSGeo/proj.4/issues/834> > > <https://github.com/OSGeo/proj.4/issues/834 > <https://github.com/OSGeo/proj.4/issues/834>> > > > > /Kristian > > > > -----Oprindelig meddelelse----- > > Fra: Qgis-user [mailto:[email protected] > <mailto:[email protected]> > > <mailto:[email protected] > <mailto:[email protected]>>] På vegne af Benjamin Ducke > > Sendt: 5. marts 2018 10:18 > > Til: [email protected] > <mailto:[email protected]> <mailto:[email protected] > <mailto:[email protected]>> > > Emne: Re: [Qgis-user] Pseudo Mercator(OSM) @ EPSG:4326 bug? > > > > Could it be this: > > > > > > http://proj4.org/faq.html#changing-ellipsoid-why-can-t-i-convert-from-wgs84-to-google-earth-virtual-globe-mercator > > <http://proj4.org/faq.html#changing-ellipsoid-why-can-t-i-convert-from-wgs84-to-google-earth-virtual-globe-mercator> > > > > <http://proj4.org/faq.html#changing-ellipsoid-why-can-t-i-convert-from-wgs84-to-google-earth-virtual-globe-mercator > > <http://proj4.org/faq.html#changing-ellipsoid-why-can-t-i-convert-from-wgs84-to-google-earth-virtual-globe-mercator>> > > > > ? > > > > The further you get from the equator, the more > > obvious the discrepancy on the Y axis. > > > > Best, > > > > Ben > > > > On 05/03/18 09:38, Idan Miara wrote: > > > Hi, > > > > > > I might have found a bug related to transformation of layer CRS > > > from EPSG:3857 (Pseudo Mercator) to EPSG:4325 (WGS84 Geo). > > > I'm attaching a few images to demonstrate the issue. > > > > > > Steps to reproduce: > > > I've load OSM in QGIS 2.18.16 (or 3.0,same results) > > > via Tile Server (XYZ): > > > https://a.tile.openstreetmap.org/{z}/{x}/{y}.png > <https://a.tile.openstreetmap.org/{z}/{x}/{y}.png> > > <https://a.tile.openstreetmap.org/{z}/{x}/{y}.png > <https://a.tile.openstreetmap.org/{z}/{x}/{y}.png>> > > > > <https://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png > <https://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png> > > <https://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png > <https://a.tile.openstreetmap.org/%7Bz%7D/%7Bx%7D/%7By%7D.png>>> > > > > > > Then set the CRS to EPSG:4326 (WGS84 Geo) > > > > > > I've also loaded a global bounds vector layer (EPSG:4326) > > > > > > In scale 1:100,000,000 it seems that the Pseudo Mercator > > transformation > > > to 4326 is flawed, as the OSM and the vectors are not aligned. > > > In scale 1:50,000,000 it seems OK when the extent is the > middle of the > > > map, but if I pan to the south/north it seems distorted again. > > > > > > If I set the project CRS to EPSG:3857 (Pseudo Mercator) as > the CRS of > > > the OSM tiles, so the vector layer would be transformed > instead, then > > > they do align in all scales (picture with the blue vector > layer). > > > > > > It doesn't look like a problem of precision of the > transformation from > > > 3857 to 4325 because it's way off. > > > Is that a bug or am I missing something here? > > > > > > Kind regards, > > > Idan. > > > > > > > > > > > > _______________________________________________ > > > Qgis-user mailing list > > > [email protected] <mailto:[email protected]> > <mailto:[email protected] <mailto:[email protected]>> > > > List info: > https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > > Unsubscribe: > https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > > > > > > > > > > -- > > Dr. Benjamin Ducke > > Deutsches Archäologisches Institut (DAI) > > Zentrale Berlin, IT-Referat > > * Projekt "Stunde Null" * > > _______________________________________________ > > Qgis-user mailing list > > [email protected] <mailto:[email protected]> > <mailto:[email protected] <mailto:[email protected]>> > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > Unsubscribe: > https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > _______________________________________________ > > Qgis-user mailing list > > [email protected] <mailto:[email protected]> > <mailto:[email protected] <mailto:[email protected]>> > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > Unsubscribe: > https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > <https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user>> > > > > > > > > _______________________________________________ > > Qgis-user mailing list > > [email protected] <mailto:[email protected]> > > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > > > > > -- > Dr. Benjamin Ducke > Deutsches Archäologisches Institut (DAI) > Zentrale Berlin, IT-Referat > * Projekt "Stunde Null" * > _______________________________________________ > Qgis-user mailing list > [email protected] <mailto:[email protected]> > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > <https://lists.osgeo.org/mailman/listinfo/qgis-user> > > -- Dr. Benjamin Ducke Deutsches Archäologisches Institut (DAI) Zentrale Berlin, IT-Referat * Projekt "Stunde Null" * _______________________________________________ Qgis-user mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
