[PROJ] some questions about the Barn Raising

[Even Rouault]

Eduardo,

> I want to promote the initiative "/GDAL Coordinate System Barn Raising"/
> because in Costa Rica there has recently been a change of CRS - from CRTM05
> (EPSG 5367) to CR-SIRGAS (EPSG 8906)

You meant CR-SIRGAS (EPSG *8908*) right ?

This was a very interesting use case that exhibit a few bugs in PROJ I've just 
fixed per https://github.com/OSGeo/proj.4/pull/1427 (for PROJ 6.1)

With the fixes, appropriate datum shift, using the Helmert tranformation 
registered in the EPSG dataset, is now done when attempting:

$ projinfo -s EPSG:5367 -t EPSG:8908

Candidate operations found: 1
-------------------------------------
Operation n°1:

unknown id, Inverse of Costa Rica TM 2005 + CR05 to CR-SIRGAS (1) + Costa Rica 
TM 2005, 0.5 m, Costa Rica

PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +inv +proj=tmerc +lat_0=0 
+lon_0=-84 +k=0.9999 +x_0=500000 +y_0=0 +ellps=WGS84 +step +proj=push +v_3 
+step +proj=cart +ellps=WGS84 +step +proj=helmert +x=-0.16959 +y=0.35312 
+z=0.51846 +rx=-0.03385 +ry=0.16325 +rz=-0.03446 +s=0.03693 
+convention=position_vector +step +inv +proj=cart +ellps=GRS80 +step +proj=pop 
+v_3 +step +proj=tmerc +lat_0=0 +lon_0=-84 +k=0.9999 +x_0=500000 +y_0=0 
+ellps=GRS80


> but I
> still do not understand how this comes to softwares like QGIS or PostGIS
> that are used by many types of users.

* PostGIS 3.0 will incorporate PROJ 6 support. There's already a development 
branch for it.
* QGIS 3.8dev has received initial work to support PROJ6, but that might 
perhaps take an extra dev cycle to have full support for it.
* Spatialite dev team is aware of the porting work, and will likely start 
working on that.

So this is a matter of time before PROJ 6 starts being adopted by upper level 
components of the software stack. I also think that real use of the new 
capabilities might take a few more time since some porting efforts still rely 
on using PROJ strings to describe CRS, which lose the datum information.

Even

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