[postgis/postgis] Implement ST_Distance via GEOS (#218)

[Regina Obe]

> > On Sep 26, 2024, at 9:49 AM, Regina Obe <lr at pcorp.us> wrote:
> >
> > Would there be any benefit to exposing it under a different name like
> _ST_DistanceGeos so for cases like what strk mentioned, it could be used and
> also so we can more easily compare the penalty in use.
> 
> Well, we can do that in a PR, and strk’s PR here just does the same idea only by
> retaining a ST_Distance_LWGeom, so he can performance test his branch.
> 
> >  I recall reading somewhere that in PostgreSQL 17 they improved some of
> the copy logic.  I could be completely imagining that though.
> >  Remember we just started the PostGIS 3.6 cycle, so now is the time to be a
> bit adventurous.
> 
> We do have lots of time to fix things! Fixing the precision issues would be
> back-portable though, while changing the implementation to a GEOS back-
> end, probably not.
> 
> P
> 
Okay if it's simpler to fix the local distance calc then yah we should do that.  I just wasn't sure which approach was easier.
Agree the GEOS backend would not be backportable at least the way I'm envisioning it.
I also don't know if GEOS has changed dist calcs over the years that such as change may raise more questions than solve problems.