[postgis-devel] Wobbles

[Paul Ramsey]

That seems more stable.

> On Apr 28, 2021, at 1:56 PM, Darafei Komяpa Praliaskouski <me at komzpa.net> wrote:
> 
> since it's a sum of doubles and it's order-dependant, can you try 
> 
> select sum(st_area(geom::geography) order by st_area(geom::geography)) from va;
> 
> On Wed, Apr 28, 2021 at 11:50 PM Paul Ramsey <pramsey at cleverelephant.ca> wrote:
> Yeah, looks like it wobbles. Two runs, no change in anything at all, just two SQL statements one after another
> 
> postgis=# select sum(st_area(geom::geography)) from va;
>         sum         
> --------------------
>  1070124793748.3967
> (1 row)
> 
> Time: 1345.384 ms (00:01.345)
> postgis=# select sum(st_area(geom::geography)) from va;
>         sum         
> --------------------
>  1070124793748.3954
> (1 row)
> 
> Time: 1352.277 ms (00:01.352)
> 
> 
> 
> > On Apr 28, 2021, at 1:34 PM, Regina Obe <lr at pcorp.us> wrote:
> > 
> > I know the difference is pretty small, but how did you manage to get two
> > different answers for area with just swap of GEOS or is that a typo?
> > 
> > In 3.8.3 you have  1070124793748.3967
> > 
> > In 3.9.2dev you have 1070124793748.3959
> > 
> > Is that 2 digit different just voodoo powder.
> > I thought given  the same exact machine, same version of PostGIS  and same
> > version of Proj we could count on no randomness of answers.
> > 
> > Is the answer the same each and every time you run it for a given setup or
> > does it wabble a bit?
> > 
> >> -----Original Message-----
> >> From: postgis-devel [mailto:postgis-devel-bounces at lists.osgeo.org] On
> >> Behalf Of Paul Ramsey
> >> Sent: Tuesday, April 27, 2021 4:47 PM
> >> To: PostGIS Development Discussion <postgis-devel at lists.osgeo.org>
> >> Subject: Re: [postgis-devel] Much slower processing on GEOS 3.9.0 versus
> >> 3.8.0 for geodesic area calculation
> >> 
> >> Just to stick a nail in the GEOS-version-affects-geography-area
> > conversation,
> >> I took the time to set up two builds (GEOS 3.8 and GEOS 3.9) and swapped
> >> between them without changing anything else about the system.
> >> 
> >> postgis=# select postgis_full_version();
> >> 
> >> postgis_full_version
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ---
> >> POSTGIS="3.2.0dev 3.1.0rc1-162-g46efb9f2d" [EXTENSION] PGSQL="130"
> >> GEOS="3.8.3-CAPI-1.13.4" PROJ="8.0.0" GDAL="GDAL 3.2.0, released
> >> 2020/10/26" LIBXML="2.9.4" LIBJSON="0.15" LIBPROTOBUF="1.3.3"
> >> WAGYU="0.5.0 (Internal)"
> >> 
> >> postgis=# select sum(st_area(geom::geography)) from va;
> >>        sum
> >> --------------------
> >> 1070124793748.3967
> >> (1 row)
> >> 
> >> Time: 1449.551 ms (00:01.450)
> >> 
> >> 
> >> Then stop the server, change the LD_LIBRARY_PATH to the 3.9 install
> > location
> >> and restart.
> >> 
> >> postgis=# select postgis_full_version();
> >> 
> >> postgis_full_version
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ------------------
> >> 
> > ----------------------------------------------------------------------------
> > ------
> >> POSTGIS="3.2.0dev 3.1.0rc1-162-g46efb9f2d" [EXTENSION] PGSQL="130"
> >> GEOS="3.9.2dev-CAPI-1.14.2" PROJ="8.0.0" GDAL="GDAL 3.2.0, released
> >> 2020/10/26" LIBXML="2.9.4" LIBJSON="0.15" LIBPROTOBUF="1.3.3"
> >> WAGYU="0.5.0 (Internal)"
> >> 
> >> postgis=# select sum(st_area(geom::geography)) from va;
> >>        sum
> >> --------------------
> >> 1070124793748.3959
> >> (1 row)
> >> 
> >> Time: 1439.969 ms (00:01.440)
> >> 
> >> 
> >> 
> >> There's no effect to be seen when GEOS version is the only variable in
> > play.
> >> 
> >> P
> >> _______________________________________________
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> >> postgis-devel at lists.osgeo.org
> >> https://lists.osgeo.org/mailman/listinfo/postgis-devel
> > 
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> 
> -- 
> Darafei "Komяpa" Praliaskouski
> OSM BY Team - http://openstreetmap.by/
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