[GRASSLIST:1044] Re: interpolation from vector points

[Michael Barton]

If you work with v.surf.rst parameters, you should be able to get very good
results for your interpolation.

As you imply, however, you can sometimes get better (or more accurate)
results if you limit the raster interpolation to the area of the points. You
can do this by calculating a convex hull around the points. This is the
minimum polygon that will contain all the points. You can create a convex
hull in GRASS with v.hull.

Use v.to.rast to convert the convex hull to a raster map. You can use
v.buffer to expand the convex hull a bit before you convert or use r.grow
to expand it after you convert to raster. Then specify this raster as a mask
in v.surf.rst. The resulting interpolated map will only exist in the area of
the points. 

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton



> From: Luca Penasa <luca.penasa at email.it>
> Date: Mon, 08 May 2006 11:22:32 +0200
> To: <GRASSLIST at inet.baylor.edu>
> Subject: [GRASSLIST:1031] interpolation from vector points
> 
> Iv a mapset with a lot (200) of point. Every point is a pollution
> indicator (a tree, a bush...) with many informations, one of these is a
> lichens biodiversity index.
> What i want to do is to interpolate this index value to obtain a map of
> biodiversity of the city covered by the survey.
> Iv done the interpolation (with no so good results) but now i need to
> cut the raster obtained around the external points... maybe i have to do
> something like a buffer around the external points of survey and cut the
> map obtained from interpolation. How can i do that without have 'holes'
> in the internal part of the map? is there a way to do that?
> 
> 
> Sorry for my English
> 
> Luca
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