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

[Marco Boeringa]

I am not suggesting geographiclib is a bad choice. It may well be the 
fastest and most efficient implementation out there for doing geodesic 
calculations. It is just that the current PostGIS Help documentation 
clearly suggests that switching to sphere based calculations can improve 
performance at the obvious cost of some less accuracy. And of course it 
would be interesting to know if a true sphere based implementation could 
be faster, but maybe nobody bothered to implement one as it can be a 
special case of spheroidal, IDK?

It would also be interesting to know if PostGIS uses the 'Geodesic' or 
'GeodesicExact' class of geographiclib (or corresponing option on the 
'PolygonAreaT' class). It is likely the former as it is well documented 
to be faster, but if not due to a possible need to properly support 
larger values of flattening, switching to 'Geodesic' or exposing the 
option to switch between 'Geodesic' and 'GeodesicExact' in PostGIS, 
might be an option. However, I have no idea in what situations using 
'GeodesicExact' and larger flattening values is necessary, and if 
'GeodesicExact' is a real world use case in common scenario's.

Op 2-10-2024 om 12:37 schreef Greg Troxel:
> Is there data that suggests the geographiclib calculation is taking
> longer than some other code might?  There's a lot going on in postgis,
> and without a benchmark showing it's an issue, it feels like it could be
> premature optimization.