[postgis-users] Quick/unobstrusive way to determine if a geometry has curve elements?

Paul Ramsey pramsey at cleverelephant.ca
Tue May 5 09:31:47 PDT 2015

ST_HasArc() should do what you want

On Tue, May 5, 2015 at 1:52 AM, Andrea Aime
<andrea.aime at geo-solutions.it> wrote:
> Hi,
> I have some generic build of code that are building queries to postgis
> includingthe st_simplify function, e.g:
> select st_simplify(geometry, tolerance) from mytable where ...
> This is done to optimize data transfer and overall performance when doing
> map rendering, we just get the
> geometries as "complex" as we need them to.
> However, I've found out that the function does not support curved
> geometries, all will throw an error if it
> encounters one of them, e.g.:
>> select st_simplify(geometry, 0.1) from curves;
> ERROR:  lwgeom_simplify: unsupported geometry type: CircularString
> Curved geometries are often representing a small percentage of the
> geometries, so I would like
> to keep on simplifying the geometries made of straight segments, while
> skipping simplification
> on the curved ones, so I'm looking for a way to quickly and unobstrusively
> check if geometry
> has curved portions inside of it.
> So far I've come up with this, but it's not simple, unobstrusive, probably
> not so fast due to string
> comparisons, and not general (what if I stumble into a geometry collection
> that does contain
> curve elements for example?):
> select case geometrytype(geometry) when 'CIRCULARSTRING' then geometry
>          when 'COMPOUNDCURVE' then geometry
>          when 'CURVEPOLYGON' then geometry
>          when 'MULTISURFACE' then geometry
>          when 'MULTICURVE' then geometry
>          else st_simplify(geometry,0.1)
>          end
> from curves;
> Can anybody suggest a better way, that would not require us to have the end
> user tell
> us if a table mixes in curve bits, or not?
> Cheers
> Andrea
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