[GRASS-user] [GRASSLIST:1073] Re: interpolation from vector points

[Luca Penasa]

Thanks for your help...
I tried using v.hull but the result wasn't what i hope... v.hull create 
a vector containing a polygon, a centroid and an area object... the 
command works fine but i need to obtain a more precise job... what i 
need is a polygon that connect all the external points without to 
calculate (like v.hull do) the minor length for the polygon.
Is there a way to obtain this?

besides, i had some problems buffering the vector polygon that iv 
created with v.hull... using the v.buffer on the vector with a 
buffer-value more than 70 meters i obtain a strange figure with a hole 
and too much centroid... any idea?



Michael Barton wrote:
> 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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