[GRASSLIST:2220] Re: converting GRASS data for trend surface analysis i n R

[Roger Bivand]

> Hello all
>
> I'm trying to do some trend surface analysis with GRASS data in R, but I
> with some problems:
>
> 1 - when I get the raster from GRASS, surf.ls() doesn't accept it, since
> its not in x,y,z format:
>
>> str(isobase)
> List of 1
>  $ isobases.auto: num [1:241266] 771 770 769 768 767 ...
>>
>
> So, how can I change this to a format that surf.ls() understands?
>

isobase$isobases.auto is the z argument. You can generate the x by east()
of the object returned by gmeta(), and y by north() of this object. I'm
not sure how well surf.ls() scales to this number of points, though.

> 2 - I'll try several degrees of surfaces, so I'll use surf.ls(), but
> what about residuals? can I get them with residuals()?
>
Yes, residuals() should work. Again, scaling to this number of points is
an issue. On the other hand, the residuals and fitted values will drop
straight into the GRASS location.

Roger

> thanks in advance
>
> Carlos Grohmann
>
> --
> +-------------------------------------------------+
>         Carlos Henrique Grohmann - Guano
>     Geologist - MSc Student at IGc-USP - Brazil
>        Linux User #89721  ICQ: 214752832
> +-------------------------------------------------+


-- 
Roger Bivand
NHH, Breiviksveien 40, N-5045 Bergen, Norway