[postgis-users] Function isvalid()

[Martin Davis]

Christina:

You can use the JUMP open-source spatial data manipulation tool
(http://www.jump-project.org) to validate geometries and visualize the
nature of the errors.  

In the particular case below, what looks like a multipolygon with two
component polygons is actually a single polygon with a hole that lies
outside the parent shell.

I've attached a screenshot from JUMP so you can see its capabilities.

Martin Davis, Senior Technical Architect
Vivid Solutions Inc.
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046


> -----Original Message-----
> From: Christina Biakowski [mailto:christina.biakowski at ccgis.de] 
> Sent: March 15, 2004 4:05 AM
> To: PostGIS Users Discussion
> Subject: [postgis-users] Function isvalid()
> 
> 
> Dear list,
> I wonder for which criteria the function isvalid() checks 
> geometries? I have checked my data (MULTIPOLYGON) with 
> isvalid() and now I am trying to find out where the errors 
> result from. While for a part of the geometries for which 
> isvalid() returned false the errors are quite obvious for me 
> (unclosed polygons, crossing lines without 
> intersections/nodes) a part of the not-valid-objects seem 
> quite ok for me like the following example:
> 
> SRID=31492;MULTIPOLYGON(((2597146.2 5653827.98,2597156.824 
> 5653821.184,2597160.82 5653838.11,2597164.213 
> 5653852.142,2597173.395 5653866.878,2597257.03 
> 5653936.45,2597253.37 5653989.33,2597248.112 
> 5653988.184,2597244.88 5653987.48,2597248.42 
> 5653946.81,2597245.74 5653940.22,2597167.25 
> 5653872.7,2597160.76 5653864.92,2597156.23 
> 5653856.5,2597154.17 5653850.63,2597146.2 
> 5653827.98),(2597238.78 5654011.58,2597243.1 
> 5654008.01,2597244.53 5653991.51,2597247.705 
> 5653992.204,2597253.09 5653993.38,2597251.87 
> 5654010.96,2597253.688 5654013.749,2597255.28 
> 5654016.19,2597238.78 5654011.58)))
> 
> Can anybody give me a hint?
> 
> Thank you in advance,
> 
> Christina
> 
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