[GRASS-user] Query: number of 'areas' reported in v.build output does not necessarily represent different geographical areas

Nikos Alexandris nik at nikosalexandris.net
Wed May 8 12:49:43 PDT 2013



Vincent Bainwrote:
> > Thank you Markus,
> > good news !
> > how long has it been implemented ?

Markus Metz wrote:
> The option to snap boundary vertices has been there ever since. The
> suggestion of a reasonable (assuming floating point rounding errors)
> threshold for snapping has been added 3 weeks ago, on April 19th.
> BTW, if the input polygons are supposed to not overlap each other, the
> number of centroids should be identical to the number of input
> polygons (needs to be added to the manual).

I tried to import USGS' (2011) Global Mangroves map:

# stuff copied from the map's *latest* history
v.in.ogr dsn="/geo/geodata/mangroves/usgs_mangroves/usgs_mangroves2.shp" 
output="global_mangroves_usgs_2011" min_area=0.0001 snap=0.000000000000001

2018421 input polygons
Total area: 1.47005E+11 (2750605 areas)
Overlapping area: 5.32085E+09 (41540 areas)
Area without category: 9.25489E+09 (773734 areas)

Twice the "error" message was like (even after I, by mistake, imported with 

Ended with an "error while impoting, try to import with snap 1e-14"

This means that there are still errors in the map, right?

Thanks, N

More information about the grass-user mailing list