Message-ID: <alpine.LRH.2.00.1002101841540.3457@reclus.nhh.no>
Date: 2010-02-10T17:48:35Z
From: Roger Bivand
Subject: Reversed raster after readGDAL()
In-Reply-To: <f96702321002100817y1d167f6aq9bb0d739be03217f@mail.gmail.com>
On Wed, 10 Feb 2010, Agustin Lobo wrote:
> I think I tripped on this same stone, but cannot find anything in my
> records, perhaps it's on the lost computer.
Sorry, can't find such a posting - maybe my search keys were wrong - you
could try the nabble archive.
>
> 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
>
No, it is 345.0078, 194.0195.
> NW corner in QGIS (interactive):424388.820,4685490.931
> SW corner in QGIS (interactive):424389.122,4635951.740
>
SW in R is 424389, 4635822
or SW cell centre 424561.5, 4635919.0 which is the SW corner plus 0.5* the
resolution.
Try:
GDALinfo(system.file("pictures/cea.tif", package = "rgdal")[1])
system(paste("gdalinfo", system.file("pictures/cea.tif", package =
"rgdal")[1]))
to see the oddness of gdalinfo on your raster. The SW (LL) corner is north
of the NW (UL) one. The provided raster is OK, so I guess one might think
that yours isn't?
> 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.
How is the plugin writing the GTiff?
Roger
>
>
> 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
>>
>
--
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