[postgis] distance(geometry,geometry) function

[Paul Ramsey]

> The PostGIS geometry type is different from the standard PostgreSQL
> geometry types in that (1) we support 3D (2) indexing on all types (3)
> more advanced geometries (like polygons with holes) (4) collection-type
> geometries (multi* and geometrycollection) and (5) no size limit.

And (6) support functions to make them actually useful in a GIS context.
The PostgreSQL base geometric types have been essentially rotting: none
of the core pgsql developers has a particular interest in supporting or
enhancing their use. We could have done support functionality against
the base types, but would then have been missing, as Dave notes, 3D,
holes, aggregates, indexing.  Most importantly, we would have been
unable to exceed the page size limit (8Kb) for a given feature if we
used the base types.

-- 
      __
     /
     | Paul Ramsey
     | Refractions Research
     | Email: pramsey@refractions.net
     | Phone: (250) 885-0632
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