[postgis-users] Geography/geometry

Paul Ramsey pramsey at cleverelephant.ca
Mon Jan 21 13:13:35 PST 2019

> On Jan 21, 2019, at 1:00 PM, Simon Greener <simon at spatialdbadvisor.com> wrote:
> When a geography is casted to geometry for use in the aggregate form of ST_Union (or other commands such as ST_Within) is the processing done assuming the data is projected even when geodetic?

All processing of geometry make cartesian assumptions. Processing of geography using geography native functions (no casting required) makes spherical assumptions. When you case from geography::geometry you are telling the database “please process this data using cartesian assumptions”. Do we support spherical processing for all (or even many) kinds of operations? No we do not. That’s hard. Could we in the future? Sure, it might happen.


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