[GRASS-user] problem: boundary lines double

[Markus Metz]

On Sat, Feb 26, 2011 at 1:46 PM,  <mails-foren at gmx-topmail.de> wrote:
>
> Hello Markus,
>
> thank you for your advice. Unfortunatly its not possible for me to get clean data. If I import an esri file (16 features) with the command v.in.ogr -o (the o flag is for the locations projection) I get a file with 58 features.
> Below I attached the output:
>
>
> v.in.ogr -o dsn=/home/BL2009/Bundeslaender.shp output=test4
>
> Over-riding projection check
>
> Layer: Bundeslaender
>
> Importing map 16 features...
>
[...]
>
>
> Number of nodes: 146
>
> Number of primitives: 161
>
> Number of points: 0
>
> Number of lines: 0
>
> Number of boundaries: 103
>
> Number of centroids: 58
>
> Number of areas: 60
>
> Number of isles: 45
>
> Number of areas without centroid: 2
>
> -----------------------------------------------------
>
> 119 input polygons
>
> Total area: 4.596540e+01 (60 areas)
>
> Overlapping area: 0.000000e+00 (0 areas)
>
> Area without category: 4.309415e-03 (2 areas)
> Successfully finished
>
A late response:

The 16 features are most probably multipolygons, because a total of
119 polygons are imported, e.g. islands are separate polygons but can
belong to the same Bundesland. All the warnings like e.g. "Area size
[1.8e-05], area not imported" indicate that the input shapefile was
not clean and these small areas are sliver or overlapping polygons
that are created when e.g. reprojecting or simplifying a
non-topological vector. The result of topology building at the end
indicates that the imported vector is clean.

Markus M

>
>
>
> -------- Original-Nachricht --------
>> Datum: Wed, 2 Feb 2011 15:42:15 +0100
>> Von: Markus Metz <markus.metz.giswork at googlemail.com>
>> An: mails-foren at gmx-topmail.de
>> CC: grass-user at lists.osgeo.org
>> Betreff: Re: [GRASS-user] problem: boundary lines double
>
>> On Tue, Feb 1, 2011 at 4:43 PM,  <mails-foren at gmx-topmail.de> wrote:
>> >
>> > Hello Maris,
>> >
>> > thanks a lot for replying.
>> > Yes, I imported an esri shapefile. I'd tried to clean data with v.clean
>> and with many different grass clean modules, without any success.
>> > Any other idea how to solve this issue? Maybe there is a method to
>> import esri shapefiles without saving double the boundary?
>> >
>> The imported shapefile should be clean if v.in.ogr was not used with
>> the -c flag, i.e. v.in.ogr did topological cleaning. Duplicate
>> boundaries should not exist when using v.in.ogr with default settings.
>>
>> Markus M
>>
>> >
>> > -------- Original-Nachricht --------
>> >> Datum: Thu, 27 Jan 2011 21:35:17 +0200
>> >> Von: Maris Nartiss <maris.gis at gmail.com>
>> >> An: mails-foren at gmx-topmail.de
>> >> CC: grass-user at lists.osgeo.org
>> >> Betreff: Re: [GRASS-user] problem: boundary lines double
>> >
>> >> Hello,
>> >> looks like Your data are coming from non-topological vector storage
>> >> (Shapefile?). Cleanness of data stored in non-topological formats
>> >> (i.e. Shapefile) depend on data creation software abilities to produce
>> >> cliean-look data and not are enforced by data storage, as it is in
>> >> GRASS.
>> >>
>> >> Without seeing more information, my guess would be - You imported
>> >> shapefile with areas into GRASS, still they had slivers and thus
>> >> feature count has increased. Only way out is to clean data with
>> >> v.clean and friends or by hand.
>> >>
>> >>
>> >> Maris.
>> >>
>> >> http://grass.osgeo.org/grass64/manuals/html64_user/v.clean.html
>> >>
>> >>
>> >> 2011/1/27, mails-foren at gmx-topmail.de <mails-foren at gmx-topmail.de>:
>> >> > Hello,
>> >> >
>> >> > if I import a shape (414 features) with v.in.ogr.qgis I get output
>> with
>> >> 594
>> >> > features. I had read the problem is, that a boundary line between two
>> >> > polygons get saved double. How can I manage to save as one boundary
>> line
>> >> > between two polygons?
>> >> >
>> >> > Thanks a lot in advance!
>> >> >
>> >> > Steffen
>> >> > --
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