[postgis-devel] GDAL and Proj versions for PostGIS 3

[Even Rouault]

> Can we live without proj at all? I believe most web map cases are covered
> by SRID 0, 4326, 3857, 900913 and rarely 3395. All those have
> transformations in one-two lines of math.

That's certainly one use case of PostGIS, but people use it for more exotic 
CRS transforms

> > You could still have a full spatial_ref_sys table. It is just that it has
> > a
> > risk of being unsynchronized with the PROJ database.
> 
> What happens if it is? How large is error margin, who is affected?

inconsistent results when people doing transforms with PROJ / GDAL command 
line utilities or through PostGIS ST_Transform()
In case of incorrect datum shift, error can be up to several hundred meters.

> Can we add a constraint to have just one of them filled at all times?

That's not implemented, and I'm not really willing to do it, since that would 
give incorrect results in some cases (which is already the case, where people 
regularly complain that the inappropriate datum shift is selected. For 
example, for Pulkovo-42, currently we use the datum shift of Romania, and 
Polish people complain it is not correct for their use cases (or the reverse, 
but you get the point))

Yes, coordinate tranformation is a tricky business...

Even

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