[R-sig-Geo] testing for a valid raster format before reading

[Barry Rowlingson]

On Fri, Jul 27, 2012 at 10:08 AM, Mauricio Zambrano-Bigiarini
<mauricio.zambrano at jrc.ec.europa.eu> wrote:
> Dear list,
>
> Do you know if there is any way for testing if a file can be read by the
> 'raster' command of the 'raster' package ?
>
> something like:
>
>   is.raster("myfile.asc") ....
>
>
> I'm asking because I have to read many files within several directories.
> The filenames of the maps go from XXXXXXXX.001 up to XXXXXX99.999, with
> some additional files that should be skipped of the reading process
> (which extension varies from directory to directory, e.g., .csv, .txt,
> .zip, etc).
>
>
> The error I'm getting now, which appears when trying to get information
> about the file with 'GDALinfo', is the following:
>
>
> Error in .local(.Object, ...) :
>    `lai.zip' not recognised as a supported file format.
>
> 1> traceback()
> 15: .Call("RGDAL_OpenDataset", as.character(filename), TRUE, silent,
>          PACKAGE = "rgdal")
> 14: .local(.Object, ...)
> 13: initialize(value, ...)
> 12: initialize(value, ...)
> 11: new("GDALReadOnlyDataset", filename, silent = silent)
> 10: GDAL.open(fname, silent = silent)
> 9: GDALinfo(maps.list[i])
>
>
> Thanks in advance for any help,

 You can use 'try' to run code and catch errors. See help(try) for more:

for(f in files){
 r = try(raster(f))
 if(inherits(r, "try-error")){
      warning("couldnt read ",f)
   }else{
      print(summary(r))
  }
 }