[GRASSLIST:10494] Re: help with R and GRASS6

[Roger Bivand]

Hi Carlos,

On Tue, 21 Feb 2006, Carlos "Guâno" Grohmann wrote:

> Hello list
> 
> I've away from R a while, and now I'm struggling with it...
> I read Bivand's artile in GRASS-News3, but I dindn't understant exactly how
> the data is stored in R.
> 

Please see a note in R News in November 2005 by Edzer Pebesma and me.

> If I want to make a trend-surface analysis with surf.ls(), I need the x,y
> and z coordinates of each point (or pixel), but I don't know how to get
> these values

The object returned by getSites6sp() is a SpatialPointsDataFrame. You can 
get the coordinates by saying:

pointlayer <- getSites6sp("mypoints")
coords <- coordinates(pointlayer)

and assuming z is called z:

myTSA <- surf.ls(2, x=coords[,1], y=coords[,2], z=pointlayer$z)

but you can also do TSA straight away in gstat:

myTSA_with_gstat <- gstat(id="tr2", formula = z ~ 1, data = pointlayer, 
  degree=2)

(the most recent gstat just takes the location coordinates from the
SpatialPointsDataFrame object.)

There was a thread about this recently, I think copied to:

http://grass.gdf-hannover.de/twiki/pub/GRASS/WebHome/krigingusingRGRASS6.txt

where a grid is created from the GRASS region settings to predict to.

Hope this helps,

Roger

> 
> the whole idea is to make TSA, then variogram fitting in the residuals, then
> krigging (maybe with gstat or geoR, still haven't decided)
> 
> thanks
> 
> --
> +-----------------------------------------------------------+
>               Carlos Henrique Grohmann - Guano
>   Geologist M.Sc  - Doctorate Student at IGc-USP - Brazil
> Linux User #89721  - carlos dot grohmann at gmail dot com
> +-----------------------------------------------------------+
> _________________
> "Good morning, doctors. I have taken the liberty of removing Windows 95 from
> my hard drive."
> --The winning entry in a "What were HAL's first words" contest judged by
> 2001: A SPACE ODYSSEY creator Arthur C. Clarke
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no