[GRASS-user] Number of centroids outside area: difficulty with cleaning

[Markus Metz]

On Mon, Apr 15, 2013 at 5:52 AM, RichardC <richtcooper at hotmail.com> wrote:
> I tried with a length of 1000 (which I guess should represent 1000m given the
> projection is Lambert Azimuthal Equal Area) and the with a length of 500 as
> shown below in more detail. The file I'm working with quite a large
> shapefile (50MB).
>
> Topology of original imported shapefile (Lambert Azimuthal Equal Area):
> Attaching centroids...
> Number of nodes: 33748
> Number of primitives: 44546
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 30931
> Number of centroids: 13615
> Number of areas: 13615
> Number of isles: 2817
>
>
> Topology after v.split length=500
> Attaching centroids...
> Number of nodes: 3274443
> Number of primitives: 3285241
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 3271626
> Number of centroids: 13615
> Number of areas: 1218
> Number of isles: 0
> Number of incorrect boundaries: 3271358
> Number of centroids outside area: 12397

Very strange. v.split on the original imported shapefile (not the
reprojected vector) should not produce topological errors. Can you
make the shapefile available for testing or provide a link?

Markus M

>
> Topology after v.build.polylines
> v.build.polylines input=as_bas_shp_vsplit500 at PERMANENT
> output=as_bas_shp_vsplit500_vpoly
> Attaching centroids...
> Number of nodes: 33748
> Number of primitives: 44546
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 30931
> Number of centroids: 13615
> Number of areas: 13615
> Number of isles: 2817
>
> Topology after importing into CRS WGS84 (lat long)
> Attaching centroids...
> Number of nodes: 33748
> Number of primitives: 44546
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 30931
> Number of centroids: 13615
> Number of areas: 13601
> Number of isles: 2828
> *Number of incorrect boundaries: 26
> Number of centroids outside area: 14*
>
> If the length=1000 for v.split (then followed by v.build.polylines), then
> the toplogy after importing into WGS84:
> Attaching centroids...
> Number of nodes: 33748
> Number of primitives: 44546
> Number of points: 0
> Number of lines: 0
> Number of boundaries: 30931
> Number of centroids: 13615
> Number of areas: 13602
> Number of isles: 2828
> Number of centroids outside area: 13
> *Number of duplicate centroids: 109
> Number of areas without centroid: 109*
>
>
>
> --
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