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OSGeo / proj-datumgrid

Historic repository for proj datum grids. New developments are at https://github.com/OSGeo/PROJ-data
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Add RDNAPTRANS™2018 grids for The Netherlands. #105

Closed sebastic closed 4 years ago

sebastic commented 4 years ago

The old RDNAPTRANS™2008 grids for The Netherlands (rdtrans2008.gsb & naptrans2008.gtx) are currently used in PROJ, but could not be included in proj-datumgrid due to a non-free license. Details available in: Use of RDTRANS2008 and NAPTRANS2008.pdf

The new RDNAPTRANS™2018 grids use the CC-BY-4.0 license, and come in two variants. Details available in: RDNAPTRANS2018.pdf

EPSG 9.8.6 now includes changes for RDNAPTRANS™2018:

There are still some outstanding issues which have prevented the inclusion of rdcorr2018.gsb (variant 1) in EPSG, but it's expected in a future EPSG update. For now the combination of variants needs to used (starting 1 October 2020 when the 2008 should no longer be used), instead of only the recommended variant 1.

I'm not sure if the changes to filelist.csv are correct.

CC: @Jochem-L

rouault commented 4 years ago

Perhaps one or two of the above mentionned PDF could be referenced in the description of README.EUROPE ?

sebastic commented 4 years ago

Perhaps one or two of the above mentioned PDF could be referenced in the description of README.EUROPE ?

Yes, RDNAPTRANS2018.pdf should be consulted by users, as it's the best documentation for the grids to date.

I'd rather not link to the Debian package git repo, but I guess we don't have much of a choice. grid_alternatives already does it too because the files are not easily available at the authoritative source.

rouault commented 4 years ago

@sebastic Willing to submit the corresponding PR to proj itself to register the 2 grids used by EPSG in grid_alternatives ?

Jochem-L commented 4 years ago

Variant 1 for the horizontal transformation will not be included in EPSG.

EPSG:9282 uses rdtrans2018.gsb (variant 2) for the horizontal transformation. A disadvantage is that it can not be used outside the grid bounds. When outside the grid bounds, EPSG:9281 could be used to obtain the same results as Variant 1.

EPSG:9281 uses only a 7 parameter transformation, which gives an approximated transformation with an accuracy of 25 cm.