[GRASS-user] Re: v.kernel -- how to get useful results

Aren Cambre aren at arencambre.com
Sun Feb 13 09:02:54 EST 2011

Maybe I could clarify. Here's the command:
*v.kernel --verbose input=master_grass7 output=master_grass7a_heatmap

Here's the command output:
*STDDEV: 0.000100*
*RES: 200.000000 ROWS: 1000 COLS: 1000*
*Writing output raster map using smooth parameter=0.000100.*
*Normalising factor=0.000000.*
*Maximum value in output: 0.000000e+000.*

If I change stddeviation to *100*, here's what I get:
*STDDEV: 100.000000*
*RES: 200.000000 ROWS: 1000 COLS: 1000*
*Writing output raster map using smooth parameter=100.000000.*
*Normalising factor=64826.350188.*
*Maximum value in output: 0.000000e+000.*

Either way, the resulting raster is a large salmon/pink square. I have no
idea what I'm doing wrong. I've tried varying the *stddeviation *parameter
from 100 to .0001 and some values in between, and I don't get anything
different. Heck, I just now used 1000000 and .000001 and got nothing

I was really hoping to make a high res heat map of these 2.5 million points
and overlay on to a street map layer.


On Fri, Feb 11, 2011 at 9:45 PM, Aren Cambre <aren at arencambre.com> wrote:

> I am not clear how to get useful results out of v.kernel. I have a vector
> layer imported from PostGIS that has about 2.5 million points. I want to
> make a high density raster to show where these points are clustered. I can
> get the vector layer to display in GRASS just fine, albeit without
> attributes because of http://trac.osgeo.org/grass/ticket/1274.
> It's not clear to me, based on
> http://grass.fbk.eu/gdp/html_grass64/v.kernel.html, how you can get it to
> do something besides make a big, pinkish (salmon-red?) square?
> Aren
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