[GRASS-dev] v.in.ogr: islands not recognized

Wed Feb 18 01:46:37 PST 2015

On Thu, Feb 12, 2015 at 11:16 PM, Markus Metz
<markus.metz.giswork at gmail.com> wrote:
> On Wed, Feb 11, 2015 at 9:34 PM, Markus Neteler <neteler at osgeo.org> wrote:
>> HI,
>>
>> I tried to import the NUTS3 map(s) from EU which leads to some obscur
>> warnings (see below). While most can be solved with a "mild" snapping,
>> still four islands are reported as an error.
>
> The islands are not reported as an error. The error is that 9912 areas
> (2748 areas with snap=1e-8) overlap. It is up to the user to decide if
> overlapping areas are ok or not. The G7.1 message reports that areas
> are overlapping, this might be an error or not. The G7.0 message says
> that overlapping areas are errors, which is wrong because overlapping
> areas can indeed occur.

In this case, overlapping areas are ok because NUTS_RG_03M_2010.shp
contains several different administrative levels which obviously
overlap. If you want to import only one level, use v.in.ogr
where="STAT_LEVL_ = X" with X in [0, 3]. Now there should be no more
overlapping areas.

Markus M

>
> With regard to the test data, I think I know this Europe NUTS3
> dataset. Some areas are double labeled, snapping will not help here.
> You need to look at the overlapping areas (layer=2) and you need to
> decide which label in layer=1 (the area has several labels in layer 1)
> is most probably correct (hint: search for other areas with the same
> label in layer 1).
>
> Markus M
>
>> They are Andorra, etc and
>> apparently really valid. The error message though suggests that the
>> import was not successful. Could this be fixed?
>>
>> # Download NUTS3 2010, 3M and 10M
>> # http://ec.europa.eu/eurostat/web/gisco/geodata/reference-data/administrative-units-statistical-units
>>
>> # create new location from SHP file
>> grass70 -c NUTS_BN_03M_2010.shp ~/grassdata/eu_etrs89
>> g.proj -w
>>
>> # import NUTS3 polygons (performs topology check)
>> v.in.ogr input=NUTS_RG_03M_2010.shp output=NUTS_RG_03M_00
>> ...
>> Cleaning polygons
>> -----------------------------------------------------
>> Breaking polygons...
>> ...
>> -----------------------------------------------------
>> Building areas...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> ...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>>  100%
>> 16926 areas built
>> 1325 isles built
>> Number of nodes: 113763
>> Number of primitives: 355557
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 355557
>> Number of centroids: 0
>> Number of areas: 16926
>> Number of isles: 1325
>> WARNING: Number of incorrect boundaries: 157
>> -----------------------------------------------------
>> Removing bridges...
>>  100%
>> -----------------------------------------------------
>> Registering primitives...
>> 48083 primitives registered
>> 343316 vertices registered
>> Building areas...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> ...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>>  100%
>> 16925 areas built
>> 1335 isles built
>> Attaching islands...
>>  100%
>> Number of nodes: 32451
>> Number of primitives: 48083
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 48083
>> Number of centroids: 0
>> Number of areas: 16925
>> Number of isles: 1335
>> WARNING: Number of incorrect boundaries: 36
>> WARNING: Vect_get_point_in_poly_isl(): collapsed area
>> WARNING: Unable to calculate area centroid
>> WARNING: Vect_get_point_in_poly_isl(): collapsed area
>> WARNING: Unable to calculate area centroid
>> WARNING: Vect_get_point_in_poly_isl(): collapsed area
>> WARNING: Unable to calculate area centroid
>> WARNING: Vect_get_point_in_poly_isl(): collapsed area
>> ...
>> WARNING: Unable to calculate area centroid
>> WARNING: Vect_get_point_in_poly_isl(): collapsed area
>> WARNING: Unable to calculate area centroid
>> -----------------------------------------------------
>> Finding centroids for OGR layer <NUTS_RG_03M_2010>...
>>  100%
>> -----------------------------------------------------
>> Writing centroids...
>>  100%
>> WARNING: 9912 areas represent more (overlapping) features, because polygons
>>          overlap in input layer(s). Such areas are linked to more than 1
>>          row in attribute table. The number of features for those areas is
>>          stored as category in layer 2
>> -----------------------------------------------------
>> 7007 input polygons
>> Total area: 5.75852E+12 (16925 areas)
>> Overlapping area: 5.74784E+12 (9912 areas)
>> Area without category: 5.32057E+08 (19 areas)
>> -----------------------------------------------------
>> Copying features...
>>  100%
>> Building topology for vector map <NUTS_RG_03M_2010 at PERMANENT>...
>> Registering primitives...
>> 59076 primitives registered
>> 354309 vertices registered
>> Building areas...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>> ...
>> WARNING: Area of size = 0.0 ignored
>> WARNING: Area of size = 0.0 ignored
>>  100%
>> 16925 areas built
>> 1335 isles built
>> Attaching islands...
>>  100%
>> Attaching centroids...
>>  100%
>> Number of nodes: 32451
>> Number of primitives: 59076
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 48083
>> Number of centroids: 10993
>> Number of areas: 16925
>> Number of isles: 1335
>> WARNING: Number of incorrect boundaries: 36
>> -----------------------------------------------------
>> WARNING: Errors were encountered during the import
>> Estimated range of snapping threshold: [1e-13, 1e-05]
>> Try to import again, snapping with at least 1e-13: 'snap=1e-13'
>>
>> # --> the "WARNING: Vect_get_point_in_poly_isl(): collapsed area"
>> looks like a debug message to an average user.
>>
>>
>>
>> # NEW ATTEMPT WITH SNAPPING
>> GRASS 7.0.0svn (eu_etrs89): > v.in.ogr input=NUTS_RG_03M_2010.shp
>> output=NUTS_RG_03M_2010 snap=1e-8 --o
>> ...
>> Writing centroids...
>>  100%
>> WARNING: 2748 areas represent more (overlapping) features, because polygons
>>          overlap in input layer(s). Such areas are linked to more than 1
>>          row in attribute table. The number of features for those areas is
>>          stored as category in layer 2
>> -----------------------------------------------------
>> 7007 input polygons
>> Total area: 5.75852E+12 (2759 areas)
>> Overlapping area: 5.74784E+12 (2748 areas)
>> Area without category: 5.32057E+08 (4 areas)
>> -----------------------------------------------------
>> Copying features...
>>  100%
>> Building topology for vector map <NUTS_RG_03M_2010 at PERMANENT>...
>> Registering primitives...
>> 8419 primitives registered
>> 217332 vertices registered
>> Building areas...
>>  100%
>> 2759 areas built
>> 1315 isles built
>> Attaching islands...
>>  100%
>> Attaching centroids...
>>  100%
>> Number of nodes: 4220
>> Number of primitives: 8419
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 5664
>> Number of centroids: 2755
>> Number of areas: 2759
>> Number of isles: 1315
>> -----------------------------------------------------
>> WARNING: Errors were encountered during the import
>> Estimated range of snapping threshold: [1e-13, 1e-05]
>> Try to import again, snapping with 1e-07: 'snap=1e-07'
>>
>> v.build NUTS_RG_03M_2010 error=NUTS_RG_03M_2010_errors
>> ...
>> Number of nodes: 4
>> Number of primitives: 4
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 4
>> Number of centroids: 0
>> Number of areas: 4
>> Number of isles: 4
>>
>> The "WARNING: Errors were encountered during the import" is scary
>> while it seems to be valid islands (Andorra, San Marino, two islands
>> near Rome).
>>
>> thanks
>> Markus
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