[PROJ] request for integration of optimized transformatiegrid BD72 to ETRS89

[Even Rouault]

On jeudi 14 février 2019 15:00:34 CET Kristian Evers wrote:
> Hello Karin,
> 
> As long as your grids are released on a suitable open source compatible
> license, yes it is possible to add them to PROJ. If you are quick (as in
> today) and open a pull request in the proj-datumgrid repository [0] it can
> become part of the coming version 6 of PROJ. I am not sure if
> transformations to and from EPSG:31370 will be using the grids by default
> without also modifying the source code of PROJ. Even Rouault should be able
> to clear that up though.

This grid is present in the EPSG dataset, and imported in the proj.db of PROJ 
master. So this is mostly a matter of having it installed in the PROJ_LIB 
directory.

Adding it in the grid_alternatives database of the table would also be nice so 
that it is tagged as being 'known' by PROJ with a hint to which package/URL it 
can be downloaded from

On a master checkout without the grid, projinfo reports:


$ PROJ_LIB=data src/projinfo -s EPSG:4313 -t EPSG:4258 -o PROJ
-------------------------------------
Operation n°1:

EPSG:15928, BD72 to ETRS89 (2), 0.2 m, Belgium - onshore

PROJ string:
+proj=pipeline +step +proj=push +v_3 +step +proj=axisswap +order=2,1 +step 
+proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=cart +ellps=intl +step 
+proj=helmert +x=-106.8686 +y=52.2978 +z=-103.7239 +rx=-0.3366 +ry=0.457 
+rz=-1.8422 +s=-1.2747 +convention=coordinate_frame +step +inv +proj=cart 
+ellps=GRS80 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step 
+proj=axisswap +order=2,1 +step +proj=pop +v_3

-------------------------------------
Operation n°2:

unknown id, Null geographic offset from Belge 1972 to ETRS89, unknown 
accuracy, World

PROJ string:


-------------------------------------
Operation n°3:

EPSG:8369, BD72 to ETRS89 (3), 0.01 m, Belgium - onshore

PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert 
+xy_in=deg +xy_out=rad +step +proj=hgridshift +grids=bd72lb72_etrs89lb08.gsb 
+step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1



Now if I create a fake (or true...) grid bd72lb72_etrs89lb08.gsb in data,

-------------------------------------
Operation n°1:

EPSG:8369, BD72 to ETRS89 (3), 0.01 m, Belgium - onshore

PROJ string:
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert 
+xy_in=deg +xy_out=rad +step +proj=hgridshift +grids=bd72lb72_etrs89lb08.gsb 
+step +proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1

-------------------------------------
Operation n°2:

EPSG:15928, BD72 to ETRS89 (2), 0.2 m, Belgium - onshore

PROJ string:
+proj=pipeline +step +proj=push +v_3 +step +proj=axisswap +order=2,1 +step 
+proj=unitconvert +xy_in=deg +xy_out=rad +step +proj=cart +ellps=intl +step 
+proj=helmert +x=-106.8686 +y=52.2978 +z=-103.7239 +rx=-0.3366 +ry=0.457 
+rz=-1.8422 +s=-1.2747 +convention=coordinate_frame +step +inv +proj=cart 
+ellps=GRS80 +step +proj=unitconvert +xy_in=rad +xy_out=deg +step 
+proj=axisswap +order=2,1 +step +proj=pop +v_3

So the grid would be used in priority

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