[R-sig-Geo] how to go from SpatialGrid to SpatialGridDataFrame ?

[Edzer J. Pebesma]

A Horacio Samaniego wrote:

>I wonder how I should go from a SpatialGrid to a SpatialGridDataFrame.
>
>  
>
Using for example the function SpatialGridDataFrame()

>I have defined a grid using the functions from the sp, gstat and spgrass6 
>packages:
>
>G<-gmeta6()
>kk<-SpatialGrid(GridTopology(c(G$south,G$west),c(G$nsres,G$ewres),c(G$rows,G$cols)),alb.proj)
>  
>
>>str(kk)
>>    
>>
>Formal class 'SpatialGrid' [package "sp"] with 5 slots
>   ..@ grid       :Formal class 'GridTopology' [package "sp"] with 3 slots
>   .. .. ..@ cellcentre.offset: num [1:2] -1333373 -2356259
>   .. .. ..@ cellsize         : num [1:2] 1000 1000
>   .. .. ..@ cells.dim        : int [1:2] 2899 4615
>   ..@ grid.index : int(0)
>   ..@ coords     : num [1:2, 1:2] -1333373  1564162 -2356259  2257928
>   .. ..- attr(*, "dimnames")=List of 2
>   .. .. ..$ : NULL
>   .. .. ..$ : chr [1:2] "coords.x1" "coords.x2"
>   ..@ bbox       : num [1:2, 1:2] -1333872 -2356759  1564662  2258428
>   .. ..- attr(*, "dimnames")=List of 2
>   .. .. ..$ : chr [1:2] "coords.x1" "coords.x2"
>   .. .. ..$ : chr [1:2] "min" "max"
>   ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
>   .. .. ..@ projargs: chr "+proj=aea +lat_1=29.75 +lat_2=45.25 +lat_0=37.5 
>+lon_0=-96 +x_0=0 +y_0=0 +no_defs +a=6378137 +rf=298.257222101 
>+towgs84=0.000,0"| __truncated__
>
>Now I try to interpolate on that grid, with no success:
>interp.vals<-idw(var1~1,data,newdata=kk)
>Error in idw(corrext ~ 1, data = data.new_alb[gd.glm, ], newdata = 
>data.grd) :
> 	no direct or inherited method for function 'idw' for this call
>
>So, I guess that I need to have a 'SpatialGridDataFrame' instead of just 
>'SpatialGrid' as the interpolation needs to be assigned to a spatial 
>location
>  
>
newdata can be of class SpatialGrid; probably idw fails because
of the data argument. What is the class of data.new_alb[gd.glm,] ?

>kk2<-as(kk,'SpatialGridDataFrame');
>Formal class 'SpatialGridDataFrame' [package "sp"] with 6 slots
>   ..@ data       :Formal class 'AttributeList' [package "sp"] with 1 slots
>   .. .. ..@ att: list()
>   ..@ grid       :Formal class 'GridTopology' [package "sp"] with 3 slots
>   .. .. ..@ cellcentre.offset: num [1:2] -1333373 -2356259
>   .. .. ..@ cellsize         : num [1:2] 1000 1000
>   .. .. ..@ cells.dim        : int [1:2] 2899 4615
>   ..@ grid.index : int(0)
>   ..@ coords     : num [1:2, 1:2] -1333373  1564162 -2356259  2257928
>   .. ..- attr(*, "dimnames")=List of 2
>   .. .. ..$ : NULL
>   .. .. ..$ : chr [1:2] "coords.x1" "coords.x2"
>   ..@ bbox       : num [1:2, 1:2] -1333872 -2356759  1564662  2258428
>   .. ..- attr(*, "dimnames")=List of 2
>   .. .. ..$ : chr [1:2] "coords.x1" "coords.x2"
>   .. .. ..$ : chr [1:2] "min" "max"
>   ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
>   .. .. ..@ projargs: chr "+proj=aea +lat_1=29.75 +lat_2=45.25 +lat_0=37.5 
>+lon_0=-96 +x_0=0 +y_0=0 +no_defs +a=6378137 +rf=298.257222101 
>+towgs84=0.000,0"| __truncated__
>
>promotes the grid to the correct class SpatialGridDataFrame but do not 
>assign to space for the variable. Is there any way to assign an empty 
>"slot" just as we would do for a data.frame?
>
>To sum.  I cant seem to be able to create a "slot" (or z dimension) to 
>hold the output of my interpolation. Is there any trick out there that I 
>am missing? Any help will be appreciated.
>
>thanks,
>
>H
>
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