[postgis-devel] [PostGIS] #408: Catch "Exception in LWGEOM2GEOS" in ST_IsValid

[Martin Davis]

Right, this has just been explained to me by our resident PostGIS expert 
Kevin.  To repeat his explanation, the PostgreSQL language engine is 
auto-converting the string to a Geometry type, since that's what 
st_isvalid accepts.  This is where the exception is happening - which 
means that it can't be caught inside st_isvalid.

I would humbly suggest that it would be nice to be able to prevent C 
exceptions leaking out into the SQL world where possible. Perhaps a

st_isvalid_safe(String geomWKT)

could be provided to allow users to avoid this.  (And since Kevin also 
pointed out that this doesn't allow distinguishing between Geometry and 
the new Geography type, a

st_isvalid_geog_safe(String geogWKT)

might be needed as well.

Code it up and let the users vote with their keyboards!

PostGIS wrote:
> #408: Catch "Exception in LWGEOM2GEOS" in ST_IsValid
> --------------------------+-------------------------------------------------
>   Reporter:  ddegasperi   |       Owner:  pramsey
>       Type:  enhancement  |      Status:  new    
>   Priority:  medium       |   Milestone:         
>  Component:  postgis      |     Version:  1.4.X  
> Resolution:               |    Keywords:         
> --------------------------+-------------------------------------------------
> Comment (by pramsey):
>
>  Non possible.
>
>  The '':text entry first gets passed into the text parsing routines which
>  is where the failure actually occurs, not in st_isvalid. We have had
>  internal arguments many times about where validity checking should occur,
>  and the current situation is that trivially invalid geometries (1-point
>  lines, unclosed polygons) are failed during parsing.
>
>  IMO, they shouldn't fail, but that's a personal opinion, not a consensus
>  one.
>
>   

-- 
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022