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 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]> 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]>> 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> > > /Kristian > > -----Oprindelig meddelelse----- > Fra: Qgis-user [mailto:[email protected] > <mailto:[email protected]>] På vegne af Benjamin Ducke > Sendt: 5. marts 2018 10:18 > Til: [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> > > ? > > 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/%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]> > > 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> > _______________________________________________ > 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> > > > > _______________________________________________ > 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 > -- 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
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