Hello, I am trying to import a shapefile that contains polygons. Using v.in.ogr with default settings works, but generates overlapping areas:
``` v.in.ogr input=~/path/to/data/ output=soils_omafra ... ----------------------------------------------------- 139375 input polygons Total area: 1.87116E+11 (713211 areas) Overlapping area: 465.913 (142064 areas) Area without category: 1.0631E+09 (137984 areas) ----------------------------------------------------- Copying features... Building topology for vector map <soils_omafra@PERMANENT>... Registering primitives... Building areas... WARNING: Area of size = 0.0 ignored WARNING: Area of size = 0.0 ignored WARNING: Area of size = 0.0 ignored ``` After several hours testing different values of snap and min_area, I have come up with the following: ``` v.in.ogr input=~/path/to/data/ output=soils_omafra snap=4.52e-07 min_area=10.0 ... ----------------------------------------------------- 138109 input polygons Total area: 1.87116E+11 (138565 areas) Overlapping area: 34.3593 (4 areas) Area without category: 1.0631E+09 (421 areas) ----------------------------------------------------- [no warnings reported] ``` If I increase snap any more I start creating additional areas, so I don't think I can automatically get rid of the remaining 4 areas. However, when I plot those areas and look at them, they are below the min_area threshold I've set: ``` d.what.vect map=soils_omafra ... soils_omafra@PERMANENT: Type: Area Sq_Meters: 6.307 Hectares: 0.001 Acres: 0.002 Sq_Miles: 0.0 Layer: 2 Category: 2 ... ``` My map is in a lat-long projection, and the map unit is meters. I thought setting min_area=10.0 would drop all areas smaller than 10 sq meters, but my problem areas here are only 6.3 sq meters? Have I misunderstood what min_area does, or am I setting it incorrectly? I notice that the default is 0.0001, which seems really small if the units is actually meters. More generally, I'm not sure how critical these overlapping areas are, or when I can safely ignore them. For my current project, I'm going to use the imported polygons to create rasters for analysis in R. Thank you for your time, Tyler -- plantarum.ca _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user