[GRASS-user] Correcting data errors

[Markus Neteler]

On Tue, Jan 13, 2015 at 8:41 PM, Markus Metz
<markus.metz.giswork at gmail.com> wrote:
> On Sat, Jan 10, 2015 at 7:34 PM, Fábio Dias <fabio.dias at gmail.com> wrote:
>> What would be the 'recommended' way of dealing with the 'errors' made
>> when the data is created with zero topological restrictions (and saved
>> as .shp?)
>
> For import, try to find a snapping threshold for v.in.ogr that
> produces an error-free output. Ideally the output would not only be
> error-free, but the number of centroids would match the number of
> input polygons (both are reported by v.in.ogr). The min_area option of
> v.in.ogr could also help. The bulk of the cleaning should be done by
> v.in.ogr. After that, removing small areas with v.clean tool=rmarea,
> threshold in square meters, could help. For Terraclass (and PRODES)
> which are mainly based on Landsat data, a threshold of 10 square
> meters could remove artefacts and preserve valid areas (Landsat pixel
> size is about 90 square meters). The threshold needs to be empirically
> determined.
>
> I am not aware of a standard procedure that works for all data sources.

I have taken liberty to merge this answer into

http://grasswiki.osgeo.org/wiki/Vector_topology_cleaning

markusN