On Fri, May 10, 2013 at 12:52 PM, RichardC <[email protected]> wrote: > Hi Markus, > >> I assume the global mangroves map should not have overlapping >> polygons, therefore as long as there are overlapping areas and/or the >> number of centroids is not equal to the number of input polygons, more >> cleaning is needed. > > How critical is it that the number of input polygons = number of centroids?
It depends on what is (supposed to be) in the input. If the input polygons are supposed to overlap, e.g. buffers created with non-topological tools, then the number of input polygons is most likely not identical to the number of centroids which is perfectly ok. > For example, I've imported a a different shapefile with 6842 input polygons > and after importing (with 1e-12 snapping threshold) there are 6800 > centroids. Further cleaning does not change the topology. It could be that some of the input polygons are exact duplicates. > Also can I ignore > the areas without centroids? Yes, these are typically holes in polygons, e.g. a patch of non-mangrove surrounded by mangrove. > > Number of nodes: 17265 > Number of primitives: 20687 > Number of points: 0 > Number of lines: 0 > Number of boundaries: 13887 > Number of centroids: 6800 > Number of areas: 10521 > Number of isles: 7099 > Number of areas without centroid: 3721 > > Would I be correct in saying that a layer is topologically correct and needs > no further cleaning provided, there are no (i.e, zero): > 1. overlapping areas; > 2. incorrect boundaries; > 3. centroids outside area; and > 4. duplicate centroids. > While: > 5. areas without centroids can be ignored. Yes, with the exception of overlapping areas. They may or may not be correct, depending on the input. Markus M > > Many thanks, for your feedback. > > Richard > > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Query-number-of-areas-reported-in-v-build-output-does-not-necessarily-represent-different-geographics-tp5052007p5052530.html > Sent from the Grass - Users mailing list archive at Nabble.com. > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
