[postgis-devel] Re: Q3C

[Mark Cave-Ayland]

Paul Ramsey wrote:

> My current thought is an automagical planar projection into an
> appropriate UTM zone or polar stereographic system, based on the
> centroid of the feature. With the extra complication of first looking
> into the projection cache to see what the last projection used was,
> and if it's close enough, using that. Hopefully that way, in the case
> of st_function(geog1, geog2) the two arguments would be both cast into
> the same plane. This would magically allow the geography module to
> make use of all the geometry functions, and only break for really
> large objects that exceed our chosen planar areas.
> 
> P.

I must say that I'm not a particular fan of this approach, since I can't 
see a way for the user to know what level of accuracy they are getting 
for any particular calculation. Plus having some operations randomly 
fail because they cross certain points/areas is just going to be a 
nightmare to support.

I'd like to see a geography type implemented as a pure angular 
calculation set with its own set of related functions derived from 
angular arithmetic, plus with its own geodetic indexing scheme. I don't 
see the value in just re-hashing what we have with a different type so 
we can claim geodetic support, when in fact the reality is very different.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
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