Here I am again... I'm facing a topological problem, surely due to my ignorance. I've dissolved a polygonal layer, composed by polygons sharing boundaries and isolated polygons, with various holes within each polygon. I created a foo column and have assigned value for all the features, to be able to dissolve every boundary between adjacent areas. The result has the following topology composition:
nodes=386 points=0 lines=0 boundaries=375 centroids=11 areas=21 islands=21 faces=0 kernels=0 primitives=386 map3d=0 type count min max point 0 0 0 line 0 0 0 boundary 0 0 0 centroid 11 1 1 area 0 0 0 all 11 1 1 First question: the topology dump tells me that I have 21 areas and 21 isles, bu the "true" areas are 11. I've read with attention the dump, and I can see that the holes in the original polygons now are considered both as areas (with no centroid) and isles... Shouldn't be considered only an island or an area depending on the lines "signs"? Anyway, the problem is that if now I build the topology on this dissolved layer, I get isles "transformed" to areas getting centroids attached to them. That doesn't sound me conceptually correct. Could you explain me why? Second question: if I use v.category to differentiate the categories (using "sum" option) and select only "centroids", the result remains unchanged respect to the original. Things change if I select also "area". In this case... the categories get changed, but now I have 21 centroids: not only the effective areas, but also isles/areas receive centroids! So, my question is: I just want my 11 "true" areas have categories from 1 to 11, and let the isles remain isles... How to do it? (Third question): would it be possible, in the future of grass, not having to produce a second output vector when updating categories, dissolving boundaries, etc.? It would simply mean that the original get overwritten by the "new" one... Thanks, and sorry for the long questions! Giovanni _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
