[postgis-devel] SRID / Spheroid / Units

[Paul Ramsey]

I am assuming that the GEOGRAPHY type will include an SRID and that if  
one is not defined, WGS84 parameters will be assumed. Unlike GEOMETRY,  
any measuring operation (length, distance, area) against a GEOGRAPHY  
is going to need to know the spheroid parameters in order to return an  
answer, which implies a spatial_ref_sys lookup.

I am not fond of the idea of having to do a lookup, because it's going  
to have to happen so often. Particularly for some well-known values,  
I'd like to short-circuit that process. Unfortunately that cuts  
against the grain of the spatial_ref_sys concept, which is that the  
srid numbers are in fact internal to the database, and not universal  
(srid 4326 could be anything, it's not guaranteed to be WGS84). Any  
advice or guidance? Maintain the pristine theoretical underpinnings of  
spatial_ref_sys, or bow to the universal use we have promoted, which  
is to expect the values in spatial_ref_sys.sql (and hence, EPSG  
numberings) to prevail.

P.