[GRASS-user] Density of points in a vector layer

[Dylan Beaudette]

On Wed, Jun 10, 2009 at 8:27 AM, Paolo Tome<paolo_tome at hotmail.com> wrote:
> Thanks for your reply, I tried to use v.kernel but the result is not
> very satisfactory (a raster uniformly colored of gray), I don't have
> much familiarity with the console, then I use the graphical interface of
> the application (using QGIS) . Then I can set only the "maps in
> Stdeviation units" (parameter which I did not understand the full
> meaning). Can you give me some guidance on how to obtain a better
> result? Thank you very much.

Hi Paolo,

The command line is the most flexible approach to using GRASS. When
using modules that generate raster output you need to consider the
region resolution and extent. Have a look at the raster intro
(http://grass.itc.it/grass64/manuals/html64_user/rasterintro.html).
You will need to work out a resolution that makes sense, then set it
with g.region. Finally, you will have to tinker around with the stddev
option to v.kernel for results that look right to you. Think of this
parameter as the diameter of the 'filter' in which point densities are
calculated. The size of this parameter will be a function of your
dataset and the region parameters.

This module could use an updated manual page, as its usage is somewhat
mysterious.

Cheers,
Dylan


>
> On mer, 2009-06-10 at 08:18 -0700, Dylan Beaudette wrote:
>> See v.kernel
>>
>> Cheers,
>> Dylan
>>
>> On Wed, Jun 10, 2009 at 7:42 AM, Paolo Tome<paolo_tome at hotmail.com> wrote:
>> >
>> > Hello,
>> > I'm using grass in combination with qgis; I would know how can I
>> > calculate the density of points in a vector layer. In the past I used
>> > gvsig and Sextante, in particular I used  "density kernel" tool. Which
>> > equivalent application can I use in Grass?
>> > Thank you for any useful advice!
>> > Paolo Tomè
>> >
>> >
>> >
>> > _______________________________________________
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>> > grass-user at lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/grass-user
>> >
>>
>
>
>