Hi guys!
I am using this tool with i.smap, to extract roads from a raster map...
I don't understand if is better to select differents sample of 1 type (for
example main road) or use 1 sample and incrase the number of sub-categories
during the i.gensigset process...
Thx
Luca
--
"E' molto più bello sapere qualcosa di tutto, che tutto di una cosa (Blaise
Pascal)."
GENTOO-GIS Development Team
jabber: casagrande@jabber.linux.it
I have a lot of points with a value of air-pollution for every point (these values are lichen's biodiversity index). Now i need to create a map with an interpolation procedure... iv tried using v.surf.rst, but i know the model used for interpolation works fine with terrain surfaces... does it work well for these pollution values too? Is there another interpolation model (maybe a model that works fine with pollution datas) implemented like a grass module? If not, what parameters of tension and smooth have i to use with v.surf.rst? Is there anybody else working with GRASS on pullution datas?
Thanks a lot....
Luca
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I ran into some problems recently using GRASS to interpret groundwater pollution data -- v.surf.rst tends produce regions of negative pollution (overshoots) around the edge of contaminated zones. This is because data sets for pollution studies are often a bit 'extreme' with maybe three orders of magnitude difference of attribute value between some adjacent points. My solution was two step -- first crank up the tension (I used values of up to 1500) to pull the surface as tight as possible and eliminate the negatives. If that didn't work, I log transformed the data to 'calm it down' for graphic presentation purpose (that's probably how you would contour it by hand anyway). v.surf.rst does allow you to account for anisotropy (an elongated plume for example) with 'theta' and 'scalex'. But of course you have to know roughly what the anisotropy is first in order to use this feature.
I'd also like to know if there's a better way to deal with this problem.
Stuart
On Apr 19, 2006, at 4:57 AM, Luca Penasa wrote:
I have a lot of points with a value of air-pollution for every point (these values are lichen's biodiversity index). Now i need to create a map with an interpolation procedure... iv tried using v.surf.rst, but i know the model used for interpolation works fine with terrain surfaces... does it work well for these pollution values too? Is there another interpolation model (maybe a model that works fine with pollution datas) implemented like a grass module? If not, what parameters of tension and smooth have i to use with v.surf.rst? Is there anybody else working with GRASS on pullution datas?
Thanks a lot....
Luca
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