[QGIS-Developer] proj5 and epsg:3857 ?

[Jeff McKenna]

Thanks Kristian.

This experience shows us how today in the world of mapping "services" 
(remote mapping engines like QGIS, MapServer, PostGIS, GRASS GIS,..) 
rely on this unfortunate projection (thanks Google ha), where end-users 
of the services really have no access to the remote server's PROJ 
settings.  It feels like I have been battling this projection for 15 
years now ha.  -jeff



On 2018-03-09 5:39 AM, Kristian Evers wrote:
> All,
> 
> Just to follow up on this, since I am the one to blame for this error to show up.
> Both by introducing it in the first place and by releasing 5.0.0 with this as a
> known bug. The bug was introduced to fix a range of other potential issues.
> Unfortunately the architecture in the old API of PROJ makes it almost impossible
> to both treat other transformations correct while also treating the Web Mercator
> correctly. The problem is that the Web Mercator is, geodetically speaking, an
> abomination of a transformation. It basically defies all logic. This has been known
> for a long time of course. Unfortunately no tests were set up to catch this specific
> transformation. I'll make sure to at least add Jeff's test case.
> 
> Regarding releasing the library with this bug included. The cause of the problem
> was determined very close to the release time (which was announced a month
> ahead). We did go through six release candidates. The vote for promotion of RC6
> to final release was already started so I decided to release anyway since I did not
> want to prolong the process even more. I am sure this bug would have been
> discovered earlier if all of you QGIS developers would not have been super
> busy with QGIS 3.0 and had had some spare time to test the PROJ release
> candidates. I am not blaming anyone, it is just a case of bad timing. Not much
> we can do about that really. Had I been in your shoes I would not have prioritized
> testing other software either, that's for sure!
> 
> The problem has an easy fix. Remove the "+nadgrids=@null" from your epsg
> init-file and the transformation should work as expected. A proper fix will
> come in 5.0.1 around April 1st.  I hope you all will continue to use PROJ 5.0.0
> in your development builds despite this problem so other bugs can see the
> light of day and be fixed in time for 5.0.1.
> 
> I completely agree with not requiring 5.0.0 as a dependency for QGIS. Hopefully
> 5.0.1 is a little better so that can be the recommended PROJ version for QGIS.
> 
> I would like to encourage you to take a look at the release schedule [0] for the next
> couple of years. We are going to change things in order to keep up with current
> geodetic developments in countries such as Australia, USA and Iceland.  It will
> affect QGIS sooner or later. I am of course happy to provide assistance where
> needed.
> 
> /Kristian
> 
> [0] https://github.com/OSGeo/proj.4/milestones?direction=asc&sort=due_date&state=open
> 
> -----Oprindelig meddelelse-----
> Fra: QGIS-Developer [mailto:qgis-developer-bounces at lists.osgeo.org] På vegne af Jeff McKenna
> Sendt: 8. marts 2018 12:50
> Til: qgis-developer at lists.osgeo.org
> Emne: Re: [QGIS-Developer] proj5 and epsg:3857 ?
> 
> Hi Richard,
> 
> You can read my report to the PROJ team while I was testing the release
> candidates:
> http://lists.maptools.org/pipermail/proj/2018-February/008082.html
> Sorry, it is a long thread.  I was trying to prevent (this here in QGIS,
> for example) from happening, before the release.
> 
> -jeff
> 
> 
> 
> 
> 
> On 2018-03-07 4:13 PM, Richard Duivenvoorde wrote:
>> Hi,
>>
>> Having a geocoder plugins, in 2.18 (still proj4), I can geocode my home
>> address, and reproject the epsg:28992 coordinate fine to epsg:3857.
>>
>> But since last week Debian has proj5, and the same plugin (in QGIS
>> master) now is off by 500 meter.
>>
>> To reproduce: if you have a QGIS 2.18 with proj4, and the
>> 'pdokservicesplugin' geocode the zip+number: '2022zj 23' in for example
>> the osm xyz layer.
>> Now do the same in QGIS master with proj5 and you'll see it is not going
>> to the right/same position.
>>
>> Another observation: IN 2.18 I can 'reproject' the OSM layer to for
>> example epsg:4326, and still see (little distorted) map.
>> But in QGIS3/proj5 I do not see a map anymore.
>>
>> Anybody else seeing this?
>>
>> Regards,
>>
>> Richard Duivenvoorde