[GRASS-user] raster pixel value

[Nikos Alexandris]

* Nikos Alexandris <nik at nikosalexandris.net> [2019-03-14 17:57:16 +0100]:

>* Markus Metz <markus.metz.giswork at gmail.com> [2019-03-14 17:07:49 +0100]:
>
>>On Thu, Mar 14, 2019 at 3:16 PM Nikos Alexandris <nik at nikosalexandris.net>
>>wrote:
>>>
>>>Following up, why are there differences between GDAL and GRASS GIS in
>>>the following example?
>>>
>>>This ftp://ftp.soilgrids.org/data/aggregated/5km/OCDENS_M_sl1_5km_ll.tif
>>>raster map, subject to `gdalinfo`:
>>>```
>>>gdalinfo OCDENS_M_sl1_5km_ll.tif -nogcp -nomd -norat -noct -nofl
>>>Driver: GTiff/GeoTIFF
>>>Files: OCDENS_M_sl1_5km_ll.tif
>>>Size is 7200, 2987
>>>Coordinate System is:
>>>GEOGCS["WGS 84",
>>>    DATUM["WGS_1984",
>>>        SPHEROID["WGS 84",6378137,298.257223563,
>>>            AUTHORITY["EPSG","7030"]],
>>>        AUTHORITY["EPSG","6326"]],
>>>    PRIMEM["Greenwich",0],
>>>    UNIT["degree",0.0174532925199433],
>>>    AUTHORITY["EPSG","4326"]]
>>>Origin = (-180.000000000000000,87.370000000000005)
>>>Pixel Size = (0.050000000000000,-0.050000000000000)
>>>Corner Coordinates:
>>>Upper Left  (-180.0000000,  87.3700000) (180d 0' 0.00"W, 87d22'12.00"N)
>>>Lower Left  (-180.0000000, -61.9800000) (180d 0' 0.00"W, 61d58'48.00"S)
>>>Upper Right ( 180.0000000,  87.3700000) (180d 0' 0.00"E, 87d22'12.00"N)
>>>Lower Right ( 180.0000000, -61.9800000) (180d 0' 0.00"E, 61d58'48.00"S)
>>>Center      (   0.0000000,  12.6950000) (  0d 0' 0.00"E, 12d41'42.00"N)
>>>Band 1 Block=7200x1 Type=Int16, ColorInterp=Gray
>>>  NoData Value=-32768
>>>```
>>>
>>>and GRASS GIS
>>>```
>>># create a new Location
>>>grass -c OCDENS_M_sl1_5km_ll.tif /geoyeux/grassdb/global/soil_grids/
>>>
>>># projection info
>>>g.proj -g
>>>
>>>name=WGS 84
>>>datum=wgs84
>>>ellps=wgs84
>>>proj=ll
>>>no_defs=defined
>>>epsg=4326
>>>unit=degree
>>>units=degrees
>>>meters=1.0
>>>
>>># raster info
>>>r.info -g OCDENS_M_sl1_5km_ll
>>>
>>>north=87.37
>>>south=-61.98
>>>east=180
>>>west=-180
>>>nsres=0.05
>>>ewres=0.05
>>>rows=2987
>>>cols=7200
>>>cells=21506400
>>>datatype=CELL
>>>ncats=0
>>>
>>># report non-NULL cells and their x, y grid location
>>>r.stats OCDENS_M_sl1_5km_ll -n -x > stats_x
>>>```
>>>
>>>Comparing a few single pixels via:
>>>```
>>>while read LINE;do
>>>    set -- $LINE
>>>    echo " ($1,$2)
>>>    echo "GDAL:  $(gdallocationinfo -valonly OCDENS_M_sl1_5km_ll.tif $1
>>$2)"
>>>    echo "GRASS: $3"
>>>    echo
>>>done < stats_x_head
>>>```
>>>
>>>gives
>>>```
>>> (2930,77)
>>>GDAL:  2090
>>>GRASS: 2096
>>>
>>> (2931,77)
>>>GDAL:  2055
>>>GRASS: 2090
>>>
>>> (2932,77)
>>>GDAL:  2063
>>>GRASS: 2055
>>>
>>> (2933,77)
>>>GDAL:  2093
>>>GRASS: 2063
>>>
>>> (2934,77)
>>>GDAL:  2240
>>>GRASS: 2093
>>>
>>> (2935,77)
>>>GDAL:  2332
>>>GRASS: 2240
>>>
>>> (2936,77)
>>>GDAL:  2296
>>>GRASS: 2332
>>>
>>> (2937,77)
>>>GDAL:  2253
>>>GRASS: 2296
>>>
>>> (2938,77)
>>>GDAL:  2179
>>>GRASS: 2253
>>>
>>> (2939,77)
>>>GDAL:  2115
>>>GRASS: 2179
>>>```
>>>
>>>Why these differences?
>>
>>With r.stats -x, indexing starts with 1 (first row is 1).
>>With gdallocationinfo, indexing starts with 0 (first row is 0).
>
>Updated:
>```
>while read LINE ;do
>   set -- ${LINE}
>   echo " ($1,$2)"
>   echo "GDAL:  $(gdallocationinfo -valonly OCDENS_M_sl1_5km_ll.tif $(echo $1 - 1 |bc) $(echo $2 - 1 |bc))"
>   echo "GRASS: ${3}"
>   echo
>done < stats_x_head
>```

For the sake of clarity, since the file `stats_x_head` is a GRASS GIS
output, where indexing starts from 1:
```
while read LINE ;do
    set -- ${LINE}
    ROW=$(echo $1 -1 |bc)
    COLUMN=$(echo $2 - 1 |bc)
    echo "GDAL  ($ROW, $COLUMN): $(gdallocationinfo -valonly OCDENS_M_sl1_5km_ll.tif $ROW $COLUMN)"
    echo "GRASS ($1, $2): ${3}"
    echo
done < stats_x_head
```

will return
```

GDAL  (2929, 76): 2096
GRASS (2930, 77): 2096

GDAL  (2930, 76): 2090
GRASS (2931, 77): 2090

GDAL  (2931, 76): 2055
GRASS (2932, 77): 2055

GDAL  (2932, 76): 2063
GRASS (2933, 77): 2063

GDAL  (2933, 76): 2093
GRASS (2934, 77): 2093

GDAL  (2934, 76): 2240
GRASS (2935, 77): 2240

GDAL  (2935, 76): 2332
GRASS (2936, 77): 2332

GDAL  (2936, 76): 2296
GRASS (2937, 77): 2296

GDAL  (2937, 76): 2253
GRASS (2938, 77): 2253

GDAL  (2938, 76): 2179
GRASS (2939, 77): 2179
```

Nikos