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

Andrea Aime andrea.aime at geo-solutions.it
Tue May 5 01:52:25 PDT 2015

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)
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?


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Ing. Andrea Aime
Technical Lead

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054  Massarosa (LU)
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