[GRASS-user] Determining number of overlapping features per location after import of shape file

[Rainer M Krug]

On Mon, Jun 23, 2008 at 9:08 PM, Markus Neteler <neteler at osgeo.org> wrote:
> Rainer,
>
> I suggest to try the snap parameters of v.in.ogr first. Maybe the SHAPE
> file is full of gaps and slivers (commonly found, even in governmental
> data).
> *Small* snapping values might cure it. Be careful to not snap, say,
> Africa to a triangle :)
>
> Markus

Thanks Markus,

but the information is there. If I display the layer and select
layer=2, I see the overlapping areas, and if I click i=on them to get
information (v.what -a map=fires at simulation ...), I get the following
info:


East: 255207.46888
North: 6235456.43154

Map: fireHistory
Mapset: simulation
Type: Centroid
Line: 3202
Layer: 1
Category: 4

Driver: dbf
Database: /home/rkrug/Documents/Projects/AlienSpread/R/../grass/simulation/dbf/
Table: fireHistory
Key column: cat
cat : 4
YEAR : 2005
Layer: 1
Category: 178

Driver: dbf
Database: /home/rkrug/Documents/Projects/AlienSpread/R/../grass/simulation/dbf/
Table: fireHistory
Key column: cat
cat : 178
YEAR : 1993
Layer: 1
Category: 208

Driver: dbf
Database: /home/rkrug/Documents/Projects/AlienSpread/R/../grass/simulation/dbf/
Table: fireHistory
Key column: cat
cat : 208
YEAR : 1995
Layer: 2
Category: 3   <<---

and the one value marked by <<-- is the one which IO want to extract
into a raster or vector map.
Even if I do

v.extract input=fireHistory at simulation output=fires
type=point,line,boundary,area layer=2

it gives me the areas, but no associated attribute table.


>
> On Mon, Jun 23, 2008 at 12:13 PM, Rainer M Krug <r.m.krug at gmail.com> wrote:
>>
>> Hi
>>
>> I am importing a vector layer from a shape file as follow, and get the
>> warning below:
>>
>> > v.in.ogr  dsn=/home/rkrug/Documents/Projects/AlienSpread/data/input/
>> > layer=fireHistory output=fireHistory --overwrite
>>
>>
>> WARNING: 703 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
>>
>>
>> I am aware of that, and I want to create a raster layer with the
>> number of features overlapping in each location. As I ultimately need
>> a raster layer, I thought to use the following, but I get the error
>> message below:
>>
>> > v.to.rast  input=fireHistory layer=2 output=mf use=attr column=category
>> > --overwrite
>>
>> ERROR: Unable to get layer info for vector map
>>
>> Why is that?
>>
>> Is there another way of getting the number of overlapping features per
>> cell?
>>
>> Thanks
>>
>> Rainer
>>
>>
>> --
>> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
>> Biology, UCT), Dipl. Phys. (Germany)
>>
>> Plant Conservation Unit
>> Department of Botany
>> University of Cape Town
>> Rondebosch 7701
>> South Africa
>> _______________________________________________
>> grass-user mailing list
>> grass-user at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/grass-user
>
>
>
> --
> Open Source Geospatial Foundation
> http://www.osgeo.org/
> http://www.grassbook.org/



-- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

Plant Conservation Unit
Department of Botany
University of Cape Town
Rondebosch 7701
South Africa