[Gvsig_english] Creating density raster/isolines out of point layer

[Benjamin Ducke]

Use "Rasterization and interpolation->Density(kernel)".
You need to specify a points vector layer and a "Field".
The "Field" contains the number of events per point
or their weight (not sure here, anyone no better?).

In any case, you need to add a new field to the attribute table.
Set it to type integer and auto value "1". This will create
an event count/weight of "1" for every point in your map. Use
that field as input for "Field".

Make sure that the "Search radius" is set to a reasonable value
for your data. This is equivalent to the kernel bandwidth.
Obviously, a higher radius will smooth out local trends.

Ben

Da Kn wrote:
> Hi community,
> 
> I'm trying to create a density map/visualization out of an .shp point 
> file. The result should be as in this image: 
> http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Understanding_density_analysis
> I have no weight, time or other such parameters in my data, except the 
> spatial data in a Gauss-Krüger projection.
> S EXTANTE got a kernel density but it isn't working for me. When I use 
> the tool on my data, there only appears some kind of spotlight white in 
> the center and getting darker to the edges, but this isn't representing 
> my density at all. And most of the time the density rastermap isn't 
> appearing at all.
> Have you already got this problem? Is there a solution? After having the 
> kernel density raster map, i probably could vectorize it, getting 
> polylines which i could transform into polygons and so visualizing the 
> density on some clean vector layer.
> Or are there even easier ways to get such a result?
> I would be so thankful for some suggestions!! thanks for reading.
> 
> greetings and thanks davk
> 
> 
> 
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-- 
Benjamin Ducke
Senior Applications Support and Development Officer

Oxford Archaeology Ltd
Janus House
Osney Mead
OX2 0ES
Oxford, U.K.

Tel: +44 (0)1865 263 800 (switchboard)
Tel: +44 (0)1865 980 758 (direct)
Fax :+44 (0)1865 793 496
benjamin.ducke at oxfordarch.co.uk




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