[gdal-dev] problem with CloseRings

Wed Aug 22 10:11:25 PDT 2012

Oliver,

Would it just be a matter of counting the vertices of each polygon, 
selecting the polygons with 3 vertices, and comparing the value of the 
first and last vertex  as you are building wkt value string below? 

Doug

>The problem with your rings isn't that they are not closed, it is that
>they are degenerate.

>For instance:
>(559560.19 142169.94,559550.64 142173.43,559560.19 142169.94)

>This goes from PointA to PointB back to PointA.  It is closed, it just
>is degenerate.  It has no area.  I'm not aware of a super easy way of
>cleaning out such junk rings - you might need to explicitly test them
>and remove them if they are degenerate.

>Best regards,

Doug Newcomb 
USFWS
Raleigh, NC
919-856-4520 ext. 14 doug_newcomb at fws.gov
---------------------------------------------------------------------------------------------------------
The opinions I express are my own and are not representative of the 
official policy of the U.S.Fish and Wildlife Service or Dept. of the 
Interior.   Life is too short for undocumented, proprietary data formats.

Frank Warmerdam <warmerdam at pobox.com> 
Sent by: gdal-dev-bounces at lists.osgeo.org
08/22/2012 12:49 PM

To
Oliver Christen <oliver.christen at camptocamp.com>
cc
gdal-dev at lists.osgeo.org
Subject
Re: [gdal-dev] problem with CloseRings

Oliver,

The problem with your rings isn't that they are not closed, it is that
they are degenerate.

For instance:
(559560.19 142169.94,559550.64 142173.43,559560.19 142169.94)

This goes from PointA to PointB back to PointA.  It is closed, it just
is degenerate.  It has no area.  I'm not aware of a super easy way of
cleaning out such junk rings - you might need to explicitly test them
and remove them if they are degenerate.

Best regards,

On Wed, Aug 22, 2012 at 9:13 AM, Oliver Christen
<oliver.christen at camptocamp.com> wrote:
> dear community
>
> first of all please accept my apologies if this is not the correct
> place to ask about such question.
>
> I am trying to manipulate some geometric data using the gdal/ogr
> python lib and Im facing a problem when trying to transform invalid
> ring into valid ring.
>
> I have polygons with unclosed holes and I expected the CloseRings
> function to solve this for me, but unfortunately, that functions
> doesnt seem to do anything (in my case).
>
> see below for a simply python testcase,
>
> if you could tell me if I am possibly not using that function
> correctly or if there is a more correct way to do that, you would be
> very welcome
>
> using python version 2.6.6
> osgeo ogr lib version 1.3.40
>
> thank you very much for your attention
> best regards
> Oliver
>
> from osgeo import ogr
>
> wkt = "POLYGON ((559577.81 142165.04,559577.67 142161.79,559577.66
> 142161.16,559577.18 142139.0,559564.07 142140.84,559562.99
> 142132.4,559556.42 142134.85,559556.47 142134.96,559541.39
> 142140.58,559549.54 142162.4,559547.0200406529475
> 142163.310114102292573,559550.570425555342808
> 142173.455536680703517,559577.81 142165.04),(559559.95600777247455
> 142169.280249390256358,559550.996165407239459
> 142172.552877245907439,559550.996165407355875
> 142172.552877245907439,559547.909677243907936
> 142163.733065433305455,559550.443360350676812
> 142162.817994827404618,559542.290859716595151
> 142140.991299878398422,559557.417905980604701
> 142135.353766721702414,559557.367843619547784
> 142135.243629527511075,559562.407678314950317
> 142133.364239115995588,559563.465598454349674
> 142141.631689094298054,559576.497222575126216
> 142139.80268921770039,559576.960120304953307
> 142161.173134415294044,559576.970239149406552
> 142161.810621617711149,559577.084823867655359
> 142164.470624003995908,559577.084823867655359
> 142164.470624004025012,559570.876975534367375
> 142165.896950183814624,559564.754505693446845
> 142167.653979024267755,559564.75450569356326
> 142167.653979024296859,559559.956007772590965
> 142169.280249390256358,559559.95600777247455
> 142169.280249390256358),(559560.19 142169.94,559550.64
> 142173.43,559560.19 142169.94),(559564.97 142168.32,559560.19
> 142169.94,559564.97 142168.32),(559577.810000000172295
> 142165.04,559571.34395208011847 142166.499739240010967,559564.97
> 142168.32,559577.810000000172295 142165.04))"
>
> poly = ogr.CreateGeometryFromWkt(wkt)
>
> poly.IsValid()
> ERROR 1: IllegalArgumentException: Invalid number of points in
> LinearRing found 3 - must be 0 or >= 4
> False
>
> poly.CloseRings()
>
> poly.IsValid()
> ERROR 1: IllegalArgumentException: Invalid number of points in
> LinearRing found 3 - must be 0 or >= 4
> False
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> http://lists.osgeo.org/mailman/listinfo/gdal-dev

-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, 
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Software Developer
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