On Thu, May 9, 2013 at 8:05 AM, Nikos Alexandris <[email protected]> wrote: > RichardC wrote: > >> Hi, >> >> Snapping gives the maximum distance to another vertex in map units, degrees >> for latlon. >> >> I don't know the coordinate ref system for the world mangrove shapefile, > > Here a link to it: <http://data.unep-wcmc.org/datasets/21>. For the records, > ogrinfo reports: > > INFO: Open of `usgs_mangroves2.shp' > using driver `ESRI Shapefile' successful. > > Layer name: usgs_mangroves2 > Geometry: Polygon > Feature Count: 1432891 > Extent: (-179.950672, -38.762073) - (179.987788, 32.350173) > Layer SRS WKT: > GEOGCS["GCS_WGS_1984", > DATUM["WGS_1984", > SPHEROID["WGS_84",6378137.0,298.257223563]], > PRIMEM["Greenwich",0.0], > UNIT["Degree",0.0174532925199433]] > [cut] > > >> but if degrees lat/long, a snapping distance of 0.000001 would equate to >> ~0.1 m at the equator, which should be sufficiently small? > > My post's target was the (as Markus Metz wrote:) "suggestion of a reasonable > (assuming floating point rounding errors) threshold for snapping". > > I'd like to have a confirmation that, given that an error message/suggestion > appears still after using a snapping distance of 1e-14, it means that the > imported vector map couldn't automatically be topologically cleaned and needs > some manual handling.
Try to import with snap=1e-13 then try to import with snap=1e-12 then try to import with snap=1e-11 then try to import with snap=1e-10 etc. stop when there are no more errors Markus M > >> Does using smaller values improve topology? > > Is this a generic question or about the Global Mangroves vector map? If > generic, I don't think that topology is improved by using smaller values. If I > am not wrong, from things learned here and off-list as well, large(er) > snapping values might cause unwanted damage to the shape of the original data. > > Thanks, Nikos > _______________________________________________ > 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
