Hi, I guess the broken areas in the grass topology have dangles inside. (zoom a broken area)
use v.clean: -remove small areas and angles -delete dangles Hope it helps, Achim Νίκος Αλεξανδρής schrieb: > Felix Schalck wrote: >> While still working on my huge map of Europe, I've noticed many >> differences between the original shapefile and the grass vector layer >> created after import. > > This (probably) means that grass (i.e. v.clean) did its job and > corrected topological errors in the shapefile (?). > >> To visualize the problem, I took two >> Screenshots: >> -First one is from gqis 1.01, showing the raw >> shapefile: >> http://img214.imageshack.us/img214/4884/qgis.png >> -Second one from grass 6.4RC5, showing the imported vector >> layer: >> http://img4.imageshack.us/img4/8462/grassgis.png >> Notice how many areas seem broken in the grass layer, and how >> entire parts of large rivers (take the rhine, for an example) are >> missing. > > Not so easy to see the differences. Maybe you could (next time) > highlight them somehow. > >> The initial shapefile was patched together (from a few hundred nasa >> swbd tiles) using Markus Neteler's script (Thanks again Markus !), and >> seem to produce good results, at least in Qgis. The import command I >> used was: v.in.ogr -z -o dsn=/DATA/swbd/shp/tiles/coastlines.shp >> output=coastlines I somehow had to override the projection, because >> grass doesn't seem to recognize the projection of the shapefile - >> although both are of the same WSG84 LAT/LON proj. >> >> My question is: what went wrong ? > > Maybe nothing went wrong ;-). Check the original shape(s) there where > you can locate differences. Are there open polygons for example? > >> Perhaps there is an import step I'm >> missing, since once the 'clean' command finishes, I get an awful lot >> of areas without a centroid; I don't know. But it would be nice, for >> sure, if grass could just translate the shapefile, as it is, and allow >> me to export a *complete* vector map to inkscape. > > If its only for visualisation purposes, I think you can avoid v.clean. > Use: v.in.ogr with the flag "-c Do not clean polygons (not > recommended)". > > Or maybe v.external? > > Nikos > > _______________________________________________ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user