[postgis-users] PostGIS Geometry Clean function

[Kevin Neufeld]

Hi Horst,

Unfortunately, your script does not work with the invalid geometry 
Stefan posted today 
(http://postgis.refractions.net/pipermail/postgis-users/2008-April/019397.html).  
It quietly drops a good portion of the linework when rebuilding the 
multipolygon. 


I think the problem lies in your approach for dealing with the resultset 
from polygonize (when trying to figure out which polygons are outer 
rings and which are holes).  I think you may find that ST_BuildArea is 
much better at this type of thing than ST_Polygonize.


I modified your script slightly, by removing the entire section from 
"tmpPolygon = polygonize(tmpLinestring);" to the end of the LOOP, 
replacing it all with "outGeom = buildarea(tmpLinestring);".  This 
approach deals nicely with Stefan's error geometry.  I haven't tested it 
with other invalid cases, nor have I tested the linear portion of the 
script, but it looks promising.


Good work.
Cheers,
Kevin

Düster Horst wrote:
> In the last few days I developed a plpgsql function to clean not valid 
> polygon and linestring geometries. This function cleans all ring-self- 
> and self-intersections in PostGIS layers.
>
> The input is a valid or non valid geometry with one or more 
> self-intersections. The result is a clean Multi geometry where all 
> intersections are correct noded and divided into multiparts. I tested 
> it with polygon layers with more than 800000 objects and it works fine 
> for me. You can use the function with PostGIS >= 1.3.2. If you want to 
> use it with PostGIS 1.1.6 you have to modify the source and remove all 
> ST_ from the specific funktion names.
>
> I hope the function could be helpful for you, for me it is.
>
> Looking forward for your comments.
>
> Best regards
>
> Horst
>
> ------------------------------------------------
>
> Dr. Horst Düster
> GIS-Koordinator, Stv. Amtschef
>
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