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

Aren Cambre aren at arencambre.com
Tue Feb 15 12:20:40 EST 2011

> I had tried playing around with v.random and v.kernel to see if I could
> understand your problem, but I couldn't find any solutions so I didn't post
> it. But since you got upset with GRASS community, I will share what I found
> out anyway :)

Sorry, I am not upset!! :-) I was genuinely wondering if I didn't describe
my problem correctly or if I had posted to the wrong forum.

> I tried with different numbers of points and with different resolutions and
> I was amazed that you could make v.kernel work with 2.5 million points in a
> 200 meter resolution with a 1000000 stdeviation!! My quadcore computer took
> so much that I gave up.

Something must not be right with what I'm doing because, no matter how I
skewed the options, it took less than 200 seconds to run on my 4 year old
1.6 GHz Intel Core Duo M processor (i.e., slow).

> I noticed that it goes slower with increasing resolution, increasing number
> of points and increasing stdev. I also noticed that you have to set a much
> higher stdev for smaller resolutions and that this value is by no means
> intuitive.

Where is resolution adjusted?
http://grass.fbk.eu/gdp/html_grass64/v.kernel.html doesn't make that clear.
Am I supposed to have a pre-made raster layer already that corresponds to my
vector layer?

Hope this helps (or at least, keep you in the list :) )

I really appreciate your advice! I'm not upset with the list, was just
afraid this was too esoteric or poorly stated.

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