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

[Nicolas Ribot]

Hi Andrea,

You could use a PLPGSQL function to catch error for curved geometries and
return the geometry itself in case of error.

Then, either you put all your generic code in this function, or you just
write a wrapper around st_simplify and call it from your SQL code,
according to your needs.

Nicolas

On 5 May 2015 at 10:52, 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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