[R-sig-Geo] help to save a "SpatialPixelsDataFrame" in several image format via writeGDAL

[Barry Rowlingson]

On Tue, Sep 21, 2010 at 10:33 AM, gianni lavaredo
<gianni.lavaredo at gmail.com> wrote:
> Dear Reseachers,
>
> I wish to save a "SpatialPixelsDataFrame" in several format (ascii, tiff,
> jpg, ect ect) using writeGDAL, but I don't understand my error (it's the
> first time I use this function)
>
>
> str(grid.aggr)
> Formal class 'SpatialPixelsDataFrame' [package "sp"] with 7 slots
>  ..@ data       :'data.frame': 10816 obs. of  2 variables:
>  .. ..$ ID: Factor w/ 10816 levels "1","2","3","4",..: 1 2 3 4 5 6 7 8 9 10
> ...
>  .. ..$ H : num [1:10816] 0.298 0.385 0.378 0.539 0.372 ...

>> writeGDAL(grid.aggr,tf, drivername="GTiff", type="Byte", options=NULL)
> *Errore in create2GDAL(dataset = dataset, drivername = drivername, type =
> type, : Numeric bands required*
>
>
> thanks in advance and sorry for desturb

Error is "Numeric bands required" and at least one of your bands
("ID") is a Factor - you cant have factors (or character variables) in
GTiffs. Convert them or drop them:

 >    m = SpatialPixelsDataFrame(points = meuse.grid[c("x", "y")],
data = meuse.grid)
 >   writeGDAL(m,"junk.tiff",drivername="GTiff", type="Byte", options=NULL)

Error in create2GDAL(dataset = dataset, drivername = drivername, type
= type,  :
  Numeric bands required

 - so lets convert the ffreq variable to numeric:

 > m$ffreq=as.numeric(m$ffreq)
 > writeGDAL(m,"junk.tiff",drivername="GTiff", type="Byte", options=NULL)

 - and that works.

Barry


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