Re: Sphere based calculations for geography don't appear to be faster?

> On Oct 1, 2024, at 1:18 PM, Regina Obe <[email protected]> wrote:
> 
> This does not surprise me.  I think Paul wrote that note 15 years ago and even then I don't recall it making a significant difference and back then we weren't even using geographylib and think we are now even for sphere.
> We should probably take that not out of the docs.
> 
> Paul you have anything to say about the below? Does it make a difference maybe if you have a narly multipolygon with 5,000,000 points?

No idea. But I bet if you trace the code you’ll find that area uses the geographiclib code in both spherical and spheroidal mode, it just sets the major and semi-major axes equal for the spherical mode. I haven’t confirmed that, but my best guess.

P

> 
>> -----Original Message-----
>> From: Marco Boeringa 
>> Subject: Sphere based calculations for geography don't appear to be faster?
>> 
>> Hi,
>> 
>> After the PostGIS 3.4.3 release, that fixed an issue with sphere based
>> calculations for geography type, I decided to run a quick test to see if sphere
>> based calculations would give a performance benefit for my workflow. Due to
>> the existing bug, I had been using spheroid based calculations exclusively up to
>> now.
>> 
>> According to the Help (https://postgis.net/docs/ST_Area.html), the sphere
>> based calculations should be faster. However, looking at the timings listed
>> below, it appears there is no significant difference?
>> 
>> SQL used:
>> 
>> DROP MATERIALIZED VIEW IF EXISTS atest;
>> CREATE MATERIALIZED VIEW atest AS SELECT
>> ST_AREA(way::geography,true/false) FROM planet_osm_polygon
>> 
>> The test data was the Geofabrik Italy extract, and used the polygon table of an
>> osm2pgsql import containing +/- 19M records, containing polygons of varying
>> sizes up to country size. The tests were run on a local dedicated system with
>> plenty of IO and CPU.
>> 
>> Marco
>> 
>> *** SPHEROID ***:
>> Start time    2024-10-01 08:07:05.984
>> Finish time    2024-10-01 08:07:15.248
>> 
>> Start time    2024-10-01 08:08:13.881
>> Finish time    2024-10-01 08:08:24.362
>> 
>> Start time    2024-10-01 08:08:42.772
>> Finish time    2024-10-01 08:08:51.998
>> 
>> Start time    2024-10-01 08:09:16.137
>> Finish time    2024-10-01 08:09:26.484
>> 
>> *** SPHERE ***
>> Start time    2024-10-01 08:10:35.261
>> Finish time    2024-10-01 08:10:45.846
>> 
>> Start time    2024-10-01 08:11:05.856
>> Finish time    2024-10-01 08:11:16.110
>> 
>> Start time    2024-10-01 08:11:35.278
>> Finish time    2024-10-01 08:11:44.499
>> 
>> Start time    2024-10-01 08:12:18.769
>> Finish time    2024-10-01 08:12:29.020
>