[R-sig-Geo] Problem when loading GRASS 6 raster with large integer values

[Roger Bivand]

On Tue, 16 Sep 2008, Rainer M Krug wrote:

> Hi
>
> when I try to import a raster layer from grass with large integer
> values, I get wrong values in R (see below). When I change the
> datatype in GRASS to double, it works.

The underlying r.out.bin exports CELL rasters as short integers using two 
bytes only, and the 6.3 version of the module has no option or flag for 
setting this differently. So conversion to DCELL (or FCELL) is the only 
fix.

Roger

>
> Thanks,
>
> Rainer
>
>
>
> GRASS 6.3.0 (grass):~/Documents/Projects/AlienSpread/R > r.stats -c
> input=tmpDispLocal
> 100%
> 0 39798
> 11 831
> 58 78
> 105 38
> 242 1652
> 889 816
> 2205 294
> 2310 56
> 3315 1171
> 4935 116
> 7875 9
> 8085 67
> 11550 6
> 13010 299
> 24675 2
> 30135 425
> 47702 1
> 48510 981
> 103635 1255
> 165375 8
> 177797 160
> 177870 6
> 379995 324
> 606375 8
> 662970 292
> 1416345 445
> 2260125 41
> * 50661
> [Raster MASK present]
>
>
> BUT:
>
>
>>     seeds <- readRAST6(
> +                        "tmpDispLocal",
> +                        ignore.stderr=!Debug
> +                        )
> Creating BIL support files...
> Header File =
> /home/rkrug/Documents/Projects/AlienSpread/R/../grass/simulation/.tmp/ecolmod/tmpDispLocal.hdr
> World File =
> /home/rkrug/Documents/Projects/AlienSpread/R/../grass/simulation/.tmp/ecolmod/tmpDispLocal.wld
> Exporting raster as integer values (bytes=2)
> Using the current region settings...
> north=6247000.000000
> south=6195000.000000
> east=270200.000000
> west=251000.000000
> r=520
> c=192
>
>> table(seeds[[1]])
>
> -31233 -27437 -25447 -18811 -18738 -17834 -17026 -13221      0     11     58
>     8   1255    445    160      6      1    981    324  39798    831     78
>   105    242    889   2205   2310   3315   4935   7610   7875   8085  11550
>    38   1652    816    294     56   1171    116    292      9     67      6
> 13010  16551  24675  30135  31901
>   299      8      2    425     41
>>
>
>
> Additional info:
>
> GRASS 6.3.0 (grass):~/Documents/Projects/AlienSpread/R > r.info map=tmpDispLocal
> +----------------------------------------------------------------------------+
> | Layer:    tmpDispLocal                   Date: Tue Sep 16 16:45:35 2008    |
> | Mapset:   simulation                     Login of Creator: rkrug           |
> | Location: grass                                                            |
> | DataBase: /home/rkrug/Documents/Projects/AlienSpread/R/..                  |
> | Title:     ( tmpDispLocal )                                                |
> | Timestamp: none                                                            |
> |----------------------------------------------------------------------------|
> |                                                                            |
> |   Type of Map:  raster               Number of Categories: 2260125         |
> |   Data Type:    CELL                                                       |
> |   Rows:         520                                                        |
> |   Columns:      192                                                        |
> |   Total Cells:  99840                                                      |
> |        Projection: UTM (zone -34)                                          |
> |            N:    6247000    S:    6195000   Res:   100                     |
> |            E:     270200    W:     251000   Res:   100                     |
> |   Range of data:    min = 0  max = 2260125                                 |
> |                                                                            |
> |   Data Description:                                                        |
> |    generated by r.mapcalc                                                  |
> |                                                                            |
> |   Comments:                                                                |
> |    round(tmpDisp * 0.300000)                                               |
> |                                                                            |
> +----------------------------------------------------------------------------+
>
> [Raster MASK present]
> GRASS 6.3.0 (grass):~/Documents/Projects/AlienSpread/R >
>
>

-- 
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