[R-sig-Geo] ASCII grids as spatialgridframe

[Roger Bivand]

On Thu, 23 Jul 2009, Els Ducheyne wrote:

> Dear all
> sorry to post this question, but I have been looking across multiple fora and 
> haven't found the answer
>
> I am trying to read ascii-grids in R using the shapefile - read.asciigrid

This is not a shapefile at all.

> I have found that this is of class SpatialGridDataFrame
> I would like to combine this with a set of grids that are already in the 
> workspace but when i use the [[<-option I always get the following error
> What am I doing wrong? I am not using rgdal, because of a linking error that 
> I cannot seem to overcome - even though the installation of rgdal and all its 
> dependencies didn't yield an erro
>
> Thanks for any help!
>
> achandata<-read.asciigrid("achan.asc")

Preferably use readGDAL() in rgdal, and note that the equivalent 
readAsciiGrid() in maptools allows for ESRI's locale oddities while the 
version in sp does not. But in general just use readGDAL().

>> summary(achandata)
> Object of class SpatialGridDataFrame
> Coordinates:
>          min    max
> coords.x1 -2.5 1002.5
> coords.x2 -2.5  502.5
> Is projected: NA
> proj4string : [NA]
> Number of points: 2
> Grid attributes:
> cellcentre.offset cellsize cells.dim
> 1                 0        5       201
> 2                 0        5       101
> Data attributes:
>  Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
> 0.0000  0.0000  0.3000  0.7088  0.9000  6.2000
>> grids[["achan"]]<-achandata

You are trying to assign a SpatialGridDataFrame object to a column in 
grids, another SpatialGridDataFrame. Why not use the cbind() method for 
these objects, for example:

grids1 <- cbind(grids, achandata)
names(grids) <- c("elev", "grad", "achan")

Alternatively, but more error-prone is:

an <- names(achandata)
grids$achan <- achandata[[an[1]]]

- the name is most likely "band1", but we don't know.

Hope this helps,

Roger

> Error: object is not subsettable
>> summary(grids)
> Object of class SpatialGridDataFrame
> Coordinates:
>          min    max
> coords.x1 -2.5 1002.5
> coords.x2 -2.5  502.5
> Is projected: NA
> proj4string : [NA]
> Number of points: 2
> Grid attributes:
> cellcentre.offset cellsize cells.dim
> 1                 0        5       201
> 2                 0        5       101
> Data attributes:
>     elev            grad
> Min.   :119.8   Min.   :0.0008663
> 1st Qu.:140.0   1st Qu.:0.0399718
> Median :144.0   Median :0.0620299
> Mean   :144.3   Mean   :0.0821328
> 3rd Qu.:150.1   3rd Qu.:0.1129532
> Max.   :159.5   Max.   :0.3284767
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo

-- 
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