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. > 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
