[postgis-users] WKT differs in PostGIS and Geos

[Maxime van Noppen]

On 07/11/09 18:57, Paragon Corporation wrote:
> Maxime,
> 
> ST_AsText does not produce the fidelity of the geometry.  It truncates
> floating points and I think where they truncate between GEOS and PostGIS is
> different.   GEOS and PostGIS do not share the same WKT writers.
> 
> My question is -- have you tried validating the WKB in GEOS.  The WKB should
> maintain fidelity so you should get the same IsValid answer in both those
> cases. 

Hi,

Thanks for the answer.

I've indeed tested the validity of the geometry loaded from the WKB in
Geos and it says it isn't valid whereas ST_IsValid says it is valid.

I've attached the test program I use. geom_1 is the WKB and geom_2 is
the WKT given by AsText. For geos both are invalid whereas for PostGIS
they're both valid.

Here is my output (i've squeezed the WKT output) :

g1->isValid : 0
g2->isValid : 0
[...]
ST_IsValid(geom1) : t

g1 is the geos::geom::Geometry corresponding to geom1.

I use the pqxx the library to perform PostGIS operations.

-- 
yabo
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