PROJ RFC 5: Adopt GeoTIFF-based grids for grids delivered with PROJ¶
- Implementation target:
- Last Updated:
This RFC is a continuation of PROJ RFC 4: Remote access to grids and GeoTIFF grids. With RFC4, PROJ can, upon request
of the user, download grids from a CDN in a progressive way. There is also API,
proj_download_file() to be able to download a GeoTIFF grid in
the user writable directory. The content of the CDN at https://cdn.proj.org
is https://github.com/OSGeo/PROJ-data , which has the same content
as https://github.com/OSGeo/proj-datumgrid converted in GeoTIFF files. In the
current state, we could have a somewhat inconsistency between users relying on
the proj-datumgrid, proj-datumgrid-[world,northamerica,oceania,europe] packages
of mostly NTv2 and GTX files, and what is shipped through the CDN. Maintaining
two repositories is also a maintenance burden in the long term.
It is thus desirable to have a single source of truth, and we propose it to be based on the GeoTIFF grids.
This change is considered to be mostly backward compatible. There might be
impacts for software using
assuming that the url returned is one of the proj-datumgrid-xxx files at
https://download.osgeo.org. As mentioned in
https://lists.osgeo.org/pipermail/proj/2020-January/009274.html , this
assumption was not completely bullet-proof either.
There will be impacts on software checking the value of PROJ pipeline strings
proj_create_crs_to_crs(). The new grid names will now
be returned (the most impacted software will likely be PROJ’s own test suite)
Although discouraged, people not using the new proj-datumgrid-geotiff-XXX.zip archives, should still be able to use the old archives made of NTv2/GTX files, at least as long as the PROJ database does not only point to a GeoTIFF grid. So this might be a short-term partly working solution, but at time goes, it will become increasingly non-working. The nominal combination will be PROJ 7.0 + proj-datumgrid-geotiff-1.0.zip
PROJ test suite will have to be adapted for the new TIFF based filenames.
Mechanism to auto-promote existing NTv2/GTX names to TIFF ones will be exercised.
The RFC was adopted on 2020-01-28 with +1’s from the following PSC members