[R-sig-Geo] Reversed raster after readGDAL()

[Agustin Lobo]

I think I tripped on this same stone, but cannot find anything in my
records, perhaps it's on the lost computer.

The file test2.tif was made by plugin Interpolation in QGIS out of a
vector layer of points with nitrate concentration values, just
a simple inverse distance method. I think that the author f that
pluginis Marco Hugentobler (Marco, sorry if it's not you) to whom I'm
forwarding.

Relevant info from the metadata in QGIS for this raster:

Layer Spatial Reference System:
+proj=utm +zone=31 +ellps=intl +units=m +no_defs

Origin
424389,4.68549e+06

Pixel Size:
279.887,-279.887

NW corner in QGIS (interactive):424388.820,4685490.931
SW corner in QGIS (interactive):424389.122,4635951.740

Image with grid: http://sites.google.com/site/eospansite/dummy/test2gridqgis.jpg

The weird thing is that QGIS uses gdal to read the geotif files.


Agus

2010/2/10 Roger Bivand <Roger.Bivand at nhh.no>
>
> On Wed, 10 Feb 2010, Agustin Lobo wrote:
>
>> Hi!
>>
>> After
>>
>>> r3 <- readGDAL("test2.tif")
>>
>> test2.tif has GDAL driver GTiff
>> and has 256 rows and 256 columns
>>
>>> image(r3,col=rainbow(128))
>>
>> I get the image N-S reversed.
>>
>> I've put an screenshot and the actual geotif image here:
>>
>> http://sites.google.com/site/eospansite/dummy/test2_screenshot2.jpeg
>> http://sites.google.com/site/eospansite/dummy/test2.tif
>
> Collected from:
>
> http://sites.google.com/site/eospansite/dummy
>
> Yes, it is flipped on the Y axis. What software made it? Could you please show the images with axes, as I think that the GTiff has a wrong sign on its y-step? What are the coordinates of the NW and SW corners of the image in QGIS? GDAL expects images to be read by row N to S, so a y-step with the wrong sign (+ instead of -) flips the image northward.
>
> Roger
>
> PS:
>
> gdalinfo externally has lower left north of upper left:
>
>> system("gdalinfo test2.tif")
>
> Driver: GTiff/GeoTIFF
> Files: test2.tif
> Size is 256, 256
> Coordinate System is:
> PROJCS["ED50 / UTM zone 31N",
>    GEOGCS["ED50",
>        DATUM["European_Datum_1950",
>            SPHEROID["International 1924",6378388,297.0000000000014,
>                AUTHORITY["EPSG","7022"]],
>            AUTHORITY["EPSG","6230"]],
>        PRIMEM["Greenwich",0],
>        UNIT["degree",0.0174532925199433],
>        AUTHORITY["EPSG","4230"]],
>    PROJECTION["Transverse_Mercator"],
>    PARAMETER["latitude_of_origin",0],
>    PARAMETER["central_meridian",3],
>    PARAMETER["scale_factor",0.9996],
>    PARAMETER["false_easting",500000],
>    PARAMETER["false_northing",0],
>    UNIT["metre",1,
>        AUTHORITY["EPSG","9001"]],
>    AUTHORITY["EPSG","23031"]]
> Origin = (424389.000000000000000,4635822.000000000000000)
> Pixel Size = (345.007812500000000,194.019531250000000)
> Metadata:
>  AREA_OR_POINT=Area
> Image Structure Metadata:
>  INTERLEAVE=BAND
> Corner Coordinates:
> Upper Left  (  424389.000, 4635822.000) (  2d 5'20.10"E, 41d52'11.88"N)
> Lower Left  (  424389.000, 4685491.000) (  2d 4'56.97"E, 42d19'2.06"N)
> Upper Right (  512711.000, 4635822.000) (  3d 9'11.42"E, 41d52'24.52"N)
> Lower Right (  512711.000, 4685491.000) (  3d 9'15.31"E, 42d19'14.90"N)
> Center      (  468550.000, 4660656.500) (  2d37'10.89"E, 42d 5'47.83"N)
> Band 1 Block=256x4 Type=Float64, ColorInterp=Gray
>
> and:
>
>> GDALinfo("test2.tif")
>
> rows        256
> columns     256
> bands       1
> origin.x        424389
> origin.y        4636016
> res.x       345.0078
> res.y       194.0195
> oblique.x   0
> oblique.y   0
> driver      GTiff
> projection  +proj=utm +zone=31 +ellps=intl +units=m +no_defs
> file        test2.tif
> apparent band summary:
>   GDType        Bmin       Bmax
> 1 Float64 -4294967295 4294967295
> Metadata:
> AREA_OR_POINT=Area
>
>
>>
>> Agus
>>
>>        [[alternative HTML version deleted]]
>>
>> _______________________________________________
>> 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
>