[postgis-users] why specify spheroid?

[Obe, Regina]

The srid of the geometry the identifier in the spatial_reference_sys
table that defines the datum, coordinates of your geometry etc of the
geometry in question).  Spatial reference system of the geometry.  If
your st_srid(the_geom)  = -1 and you fed it to
distance_sphere/distance_spheroid, it wouldn't matter as long as your
coordinates are actually measured along the ellipsoid you specify (or
approximate ellipsoid of distance_sphere).
 
The distance_sphere never takes a spheroid as I recall - and always
assumes a sphere and is faster than spheriod but less accurate.  

Hope that helps,
Regina
________________________________

From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of
Willy-Bas Loos
Sent: Tuesday, September 09, 2008 8:56 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] why specify spheroid?


> distance_sphere and distance_spheroid don't even look at the srid of
the geometry fed to them
Why is that?



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