[gdal-dev] RFC 73 (aka gdalsrsbarn) available for review

[Even Rouault]

On vendredi 25 janvier 2019 11:59:55 CET Sean Gillies wrote:
> Hi Even,
> 
> What will the impact be on spatial referencing stored in new datasets? For
> example, will users with GDAL 2.5 run gdal_translate and write WKT2 into a
> GeoTIFF, thereby creating data that can't be opened using GDAL 2.4?
> 

Hi Sean,

re-adding the list, as it is of general interest.

GeoTIFF doesn't use WKT internally ([1]), so this will have no impact, and 
datasets should be interoperable between GDAL < or >= 2.5. More generally, 
after exchanges with a few people, I've decided not to change the global 
behaviour of the exportToWKT() method: it will still export WKT1 for now. So 
the formats that currently rely on WKT to store their SRS (including GDAL and 
OGR .vrt, .aux.xml side car) will be little impacted ([2]). In a few years 
when GDAL >= 2.5 is more widespread, we might reconsider this choice.

I've reflected those changes in:
https://trac.osgeo.org/gdal/wiki/rfc73_proj6_wkt2_srsbarn?
action=diff&version=5&old_version=4

Command line utilities gdalinfo, ogrinfo and gdalsrsinfo will report WKT2 by 
default however as a hint that things have changed. gdalinfo and ogrinfo will 
gain a "-wkt_format wkt1" switch to fallback to current behaviour. gdalsrsinfo 
has already a switch to select the WKT variant), as this should have less 
impact.

Even

[1] Except as an extension of a few SRS that can't be encoded with GeoTIFF 
keys. In that case, GDAL uses a ESRI specific trick that consists in exporting 
the SRS as a ESRI WKT1 string. That behaviour will be unchanged.

[2] I write "little" and not "not" on purpose since the WKT1 export will not 
be strictly identical to previous versions. In particular AXIS, compliant with 
the ordering of the defining authority, will be output

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