Thank you Vincent and Nikos for your answers, Of course I mean v.dissolve and not r.dissolve...
Maybe I'm not clear enough wiht my problem... To explain what I want to obtain : I've created such a shapfile in qgis using the tool "add part". I have then one feature with two polygone (see attached files). Then I've imported this shapfile into GRASS and I also see one feature with two polygones. Is it possible to create such files with GRASS and in my case to merge different non-adjacent polygone into one polygone? The reason of this is I have to do statistics (v.rast.stats) with this shp and I want to consider all the features of a category for calculating the stats and the feature separated. (e.g. I want to have the mean of all pixels contained in the polygones of the same category and for each polygones separately) regards ________________________________________ De : [email protected] [[email protected]] de la part de Nikos Alexandris [[email protected]] Date d'envoi : jeudi 16 mai 2013 15:24 À : [email protected] Objet : Re: [GRASS-user] Merge polygone with same attribut of a shapefile BLANDENIER Lucien wrote: > Dear all, Hi Lucien, > I'm trying to merge all polygones with the same attribut of a shapefile. I > saw it is possible to merge adjacent polygone with r.dissolve Small correction: it is v.dissolve (all v.* modules operate on vector maps as opposed to r.* modules which operate on raster maps). > but I didn't found how to do this with polygones that are not adjacent. Is > there a way to do this? I don't know/I don't think so. GRASS' vector model is a topologically aware system. This means that it "understands", exactly, adjacent geographic components. Being so, by design, supports a clean geometry (for example, non duplication of features) and sound vector-based analyses. If I get the "picture" correct, there is no possibility to topologically merge distinct and spatially non-related geographic features. > My goal is to minimise the number of feature into my table in order to have > only one feature by category, but containing several polygones. What is the reason to worry about the number of vector features in a vector map? The only way to minimise features is by eliminating them, which is rather unwanted. You might want to read - "Vector object categories and attribute management" section in the "Vector data processing in GRASS GIS" manual: <http://grass.osgeo.org/grass64/manuals/vectorintro.html> - "Developer's Vector FAQ" <http://grass.osgeo.org/programming7/vlibFAQ.html> Each unique vector feature holds internally (that is, not exposed to the user) a unique "feature id" (this is a 1:1 relationship). The user can, however, use the concept of Categories (another identification number), to assign a vector feature to a category. Categories are not unique and they _can_ be (mis-)used to link to several vector features (this is a "1 Cat":"Many vector features" relationship). Note, the user can use them as being unique! Also, any vector feature can be linked to several category ids (this is a "1 Vector" : "Many Categories" relationship). The other interesting concept, in GRASS GIS, is the one of multiple layers. The user can link multiple attribute tables by using multiple layers (<http://grass.osgeo.org/programming7/vectorlib.html#vlibCategoriesLayers>). So, maybe (inside GRASS GIS) you simply need to assign the same category to many polygons? Best, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
test_polygones.dbf
Description: test_polygones.dbf
test_polygones.prj
Description: test_polygones.prj
test_polygones.qpj
Description: test_polygones.qpj
test_polygones.shp
Description: test_polygones.shp
test_polygones.shx
Description: test_polygones.shx
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