[Community] cascaded_union failure : No Shapely geometry can be created from null value

[Sean Gillies]

GEOS 3.2.2 should be fine.

Cheers,

On Fri, Jun 25, 2010 at 12:52 PM, Emmanuel Lambert
<emmanuel.lambert at intec.ugent.be> wrote:
> Hello Sean
>
> Thanks for you reply. I was also just about to add a follow-up comment.
>
> I upgraded my system to GEOS 3.2.2 (compile from source) and apparently
> that solved the problem. So I guess it was an issue of libgeos.
> Can I assume that Shapely 1.2.1 works fine with GEOS 3.2.2 ?
> I experience no issues at this time, but would appreciate your feedback
> on this.
>
> wbr
> Emmanuel
>
>
> On Fri, 2010-06-25 at 12:46 +0200, Sean Gillies wrote:
>> 2010/6/24 Emmanuel Lambert <emmanuel.lambert at intec.ugent.be>:
>> > Hi,
>> >
>> > Attached is a list of polygons in WKT format.
>> > I have a MultiPolygon consisting of these polygons.
>> >
>> > The cascaded_union function failes on this multipolygon.
>> > "ValueError: No Shapely geometry can be created from null value"
>> >
>> > Script to reproduce the problem :
>> >
>> > from shapely.wkt import loads
>> > from shapely.geometry import Polygon,MultiPolygon
>> > from shapely.ops import cascaded_union
>> >
>> > f = open('MULTIPOLYGON.TXT','r')
>> > polygons = []
>> > while True:
>> >     wkt = f.readline().replace("\n","")
>> >     print wkt
>> >     if len(wkt)==0:
>> >          break
>> >     pol = loads(wkt)
>> >     polygons.append(pol)
>> >
>> > mp = MultiPolygon(polygons)
>> > up = cascaded_union(mp)
>> >
>> > I have tried several strategies to work around it, but cannot get to a
>> > solution. Is this a bug in shapely, or is something wrong with my data?
>> > Your advice would be appreciated.
>> >
>> > (Shapely 1.2.1)
>> >
>> > Thanks,
>> >
>> > Emmanuel
>> >
>>
>> Hi Emmanuel,
>>
>> Before I try to reproduce this, can you run the script again and
>> assert that each polygon is valid within the loop?
>>
>>     pol = loads(wkt)
>>     assert pol.is_valid
>>     polygons.append(pol)
>>
>
>
>



-- 
Sean