Hi Paolo, > I just noticed that the centroid, as calculated by fTools, is not in the > same location as the centroid shown by the centroid fill. The difference is > easily explained in the case of multipolygons, much less obvious in case of > a compact single poligon. IIRC, the centroid as returned by fTools is based on the GEOS centroid calculation, whose documentation states: Based on the usual algorithm for calculating the centroid as a weighted sum of the centroids of a decomposition of the area into (possibly overlapping) triangles. The algorithm has been extended to handle holes and multi-polygons. See http://www.faqs.org/faqs/graphics/algorithms-faq/ for further details of the basic approach.
Not sure how the centroid fill centroid is calculated, but obviously not the same? Carson -- Carson J. Q. Farmer National Centre for Geocomputation National University of Ireland, Maynooth, http://www.carsonfarmer.com/ _______________________________________________ Qgis-developer mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-developer
