[gdal-dev] Motion: adopt RFC 81: support for coordinate epochs in geospatial formats

[Even Rouault]

Hi,

- merging the underlying API without any format support is I believe of 
little interest. So I'll wait for at least one format (likely 
GeoPackage) to have merged in the master of their specification an 
official way of storing the coordinate epoch. I've also prepared an 
enhancement of the GeoTIFF spec regarding this 
(https://github.com/opengeospatial/geotiff/pull/99) that will likely be 
discussed at the next OGC GeoTIFF SWG meeting.

- I've just chatted with Howard and a good compromise could be that for 
formats that will have an official way of storing the coordinate epoch, 
we store it by default (when it is set), and for formats that we 
unilaterally extend (GML, KML, GeoJSON, etc.), we require an explicit 
GDAL_ENABLE_COORD_EPOCH_STORAGE=YES configuration option to be set 
(default would be NO). We might revisit in the future the default value.

- On the vector side of things, things will probably get more 
complicated for some drivers, as it is likely that Spatialite (see 
https://groups.google.com/g/spatialite-users/c/NtbuBpRzYBE) or PostGIS 
might have per-geometry coordinate epoch, not at the layer level. But I 
don't think that would invalidate having support for it at the layer 
level (those database already support a per-geometry CRS, but GDAL 
support for that is probably lacking a bit in those drivers), as a 
OGRGeometry can potentially be associated with its own 
OGRSpatialReference object.

Even

Le 27/05/2021 à 15:01, Howard Butler a écrit :
>
>> On May 26, 2021, at 8:33 PM, Nyall Dawson <nyall.dawson at gmail.com> wrote:
>>
>> Can I make the suggestion that a subset of
>> https://github.com/OSGeo/gdal/pull/3827 could be created and be merged
>> on its own? Specifically the commits which add the underlying API for
>> GDAL to handle epochs should be controversy-free and suitable for
>> merge outside of the larger/trickier question of patching in support
>> to the data formats.
> :thumbsup:
>
> As for the patching of data formats with GDAL application-specific metadata, as I said, I don't have a better option, but I'm satisfied if the process of writing epochs into metadata is opt-in (some kind of global CRS option? we already have magic switches like that).
>
> Howard
>
>
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