[GRASS-user] Topology of .shp

[Martin du Saire]

Hi,

I was wondering if there was a single document that explains the 
vectors, topology, and v.in.ogr?  In particular what are the 
implications of the following messages:

Break boundaries:
Intersections:   454 (line 8471)WARNING: Vect_segment_intersection() ERROR
Intersections:  1071

Should I throw away the data?


Number of areas without centroid :   649
-----------------------------------------------------

Can areas exist in a .shp or GRASS vector without a centroid?

Does this mean that there was no centroid defined in the .shp, or 
that there was a conflict and v.in.ogr therefore did not assign a centroid?

         When I use v.in.ogr -c ... it reports

          Number of centroids outside area :   114

           When building the topology, how does v.in.ogr deal with these areas?


WARNING: 550 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.

Are these overlapping features that have centroids or any overlapping features?
How do I identify/view these?
    Would I use something like:
          v.db.connect map=mapname layer=2

3881 input polygons
total area: 3.656953e+08 (5075 areas)
overlapping area: 6.224113e+05 (550 areas)
area without category: 1.813971e+06 (649 areas)

Are these areas not assigned a category, by v.in.ogr, because of the 
lack of a centroid, or does this indicate that these areas were not 
assigned a category in the original shapefile?

Thanks.

Martin


<<The following is the complete output from v.in.ogr>>


-----------------------------------------------------
Building topology ...
4251 primitives registered
Building areas:  100%
4112 areas built
4076 isles built
Attaching islands:  100%
Attaching centroids:  100%
Topology was built.
Number of nodes     :   4160
Number of primitives:   4251
Number of points    :   0
Number of lines     :   0
Number of boundaries:   4251
Number of centroids :   0
Number of areas     :   4112
Number of isles     :   4076
Number of incorrect boundaries   :   169
Number of areas without centroid :   4112
-----------------------------------------------------
WARNING: Cleaning polygons, result is not guaranteed!
Building topology ...
Topology was built.
Number of nodes     :   4160
Number of primitives:   4251
Number of points    :   0
Number of lines     :   0
Number of boundaries:   4251
Number of centroids :   0
Number of areas     :   -
Number of isles     :   -
-----------------------------------------------------
Break polygons:
Registering points ... 64043
All points (vertices): 78582
Registered points (unique coordinates): 64043
Points marked for break:  7677
Breaks: 12727
-----------------------------------------------------
Remove duplicates:
Duplicates:  3080
-----------------------------------------------------
Break boundaries:
Intersections:   454 (line 8471)WARNING: Vect_segment_intersection() ERROR
Intersections:  1071
-----------------------------------------------------
Remove duplicates:
Duplicates:   212
-----------------------------------------------------
Clean boundaries at nodes:
Modifications:   165
-----------------------------------------------------
Break boundaries:
Intersections:     0
-----------------------------------------------------
Remove duplicates:
Duplicates:     1
-----------------------------------------------------
Clean boundaries at nodes:
Modifications:     0
-----------------------------------------------------
Change dangles to lines:
Removed dangles:     2  removed lines:     2
-----------------------------------------------------
Remove bridges:
Removed bridges:     0  removed lines:     0
-----------------------------------------------------
Building topology ...
Building areas:  100%
5075 areas built
1642 isles built
Attaching islands:  100%
Topology was built.
Number of nodes     :   8189
Number of primitives:   19151
Number of points    :   0
Number of lines     :   0
Number of boundaries:   19151
Number of centroids :   0
Number of areas     :   5075
Number of isles     :   1642
Number of areas without centroid :   5075
Layer: clu_a_mn037_cropdata_20km_cy2006
-----------------------------------------------------
-----------------------------------------------------
Building topology ...
16042 primitives registered
Building areas:  100%
5075 areas built
1642 isles built
Attaching islands:  100%
Attaching centroids:  100%
Topology was built.
Number of nodes     :   12609
Number of primitives:   16042
Number of points    :   0
Number of lines     :   0
Number of boundaries:   11616
Number of centroids :   4426
Number of areas     :   5075
Number of isles     :   1642
Number of areas without centroid :   649
-----------------------------------------------------
WARNING: 550 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.
3881 input polygons
total area: 3.656953e+08 (5075 areas)
overlapping area: 6.224113e+05 (550 areas)
area without category: 1.813971e+06 (649 areas)