[postgis-devel] Much slower processing on GEOS 3.9.0 versus 3.8.0 for geodesic area calculation

[Regina Obe]

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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