[GRASS-user] V.voronoi

[Sampson, David]

Hamish,

As usual you had the answer...  Thanks.

May I make a suggestion have a small comment added to the documentation
page at http://grass.itc.it/grass63/manuals/html63_user/v.voronoi.html
to include a note concerning setting the region. In the example it shows
a step to set the region, which makes sense now, but upon first reading
it I did not catch on.

Cheers 

-----Original Message-----
From: Hamish [mailto:hamish_nospam at yahoo.com] 
Sent: Wednesday, November 14, 2007 17:40
To: Sampson, David
Cc: grassuser at grass.itc.it
Subject: Re: [GRASS-user] V.voronoi

David Sampson wrote:

> I am ttrying to use the v.voronoi (in wingrass) tool and it is 
> perplexing me with the results I am getting. Here is the scenario.
> 
> I am trying to anaylise the spatial distribution of road
intersections.
> I started with a road network file from Statistics Canada, and clipped

> out the roads of the city of Ottawa for my subset. I created a new 
> vector containing only the nodes of the Ottawa network. The resulting 
> vector has the following basic stats ========= Type of Map:  vector 
> (level: 2)
> |
>  |   Number of points:       48156           Number of areas:      0
> |
>  |   Number of lines:        0               Number of islands:    0
> |
>  |   Number of boundaries:   0               Number of faces:      0
> |
>  |   Number of centroids:    0               Number of kernels:    0
> |
>  |
> |
>  |   Map is 3D:              0
> |
>  |   Number of dblinks:      2
> ===========
> 
> The nodes represent both road terminations and intersections.
> 
> I am new to using Voronoi charts but when I run the v.voronoi script I

> expect it to create a polygon for each node.
> 
> Instead when I run the basic stats on the new Veronoi vector I get:
> 
> =============
>  Type of Map:  vector (level: 2)
> |
>  |
> |
>  |   Number of points:       0               Number of areas:      1
> |
>  |   Number of lines:        0               Number of islands:    1
> |
>  |   Number of boundaries:   4               Number of faces:      0
> |
>  |   Number of centroids:    0               Number of kernels:    0
> |
>  |
> |
>  |   Map is 3D:              0
> |
>  |   Number of dblinks:      1        
> =============
> 
> I get a rectangular shape that is located just north of ONE of the 
> nodes in the coverage. As I zoom out some other nodes apear surounding

> rectangualr shape...  The manual doesn't shed light on my situation.
> 
> Any help, experieince or knowledge would be great.

I think that unlike most vector modules v.voronoi works in the current
region.
Try  'g.region -p vect=nodes_map'  before running v.voronoi to set the
zoom to cover all points in the input map.


?
Hamish



 
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