I have trouble bringing land cover data from the USGS into a "decent" coordinate system.

I obtained an .img file of the "Global Land Cover Characteristics Data Base Version 2.0" from http://edc2.usgs.gov/glcc/tabgeo_globe.php. I renamed the file to *.bsq and created an .hdr file according to the following description on the USGS website:

9.2 Geographic Projection Parameters

The data dimensions of the Geographic projection for the global land cover characteristics data set are 21,600 lines (rows) and 43,200 samples (columns) resulting in a data set size of approximately 933 megabytes for 8-bit (byte) images. The following is a summary of the map projection parameters used for the Geographic projection:

Projection Type: Geographic

Units of measure: arc seconds

Pixel Size: 30 arc seconds

Radius of sphere: 6370997 m.

XY corner coordinates (center of pixel) in projection units (arc seconds):

    Lower left: (-647985, -323985)

    Upper left: (-647985, 323985)

    Upper right: (647985, 323985)

    Lower right: (647985, -323985)

So I have created the following .hdr file:

nrows   21600
ncols   43200
nbands  1
nbits   8
layout  bsq
skipbytes   0
ulxmap  -647985
ulymap  323985
xdim    30
ydim    30

When I now load the file into QGIS, it looks fine. But to convert the file from the original CRS to one of my choosing, I would have to know the original CRS in the first place. And this is where I am stuck: What is the CRS of the "Global Land Cover Characteristics Data Base Version 2.0" database? Can someone tell me from the aforementioned projection infos? I tried EPSG:4326 and EPSG:3857, but they do not seem to be correct.

  • You would have to make a custom definition because none of the existing ones use arc-seconds. It would be based upon NAD83 using GRS80 ellipsoid. I found an older issue in Proj.4 about adding the ability to set the angular unit, so I'm not sure if it's supported. – mkennedy Jul 16 '15 at 16:53

Thank you @mkennedy for your input.

I am posting an answer to my own question in case anybody stumbles across this issue.

From this website here, I was able to download the same dataset, but as .tif with pre-defined CRS. Go to the EarthExplorer from this aforementioned website, choose "Land Cover / GLCC" and take the .tif file. Registration (free) is required beforehand.

I guess that's as simple as it gets.

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  • Can you add the CRS definition that QGIS uses after loading the file? – AndreJ Jul 20 '15 at 10:59
  • The .tif file comes with the standard WGS84 (EPSG:4326) out of the box. But as I mentioned in the question at the top: Applying this CRS to the .bsq file did not give any meaningful results. So I assume the USGS people have done the transformation internally, before offering the .tif as WGS84 to the public. – Bob3k Jul 20 '15 at 11:53

Converting the units to degrees, you can use this header file:

nrows   21600
ncols   43200
nbands  1
nbits   8
layout  bsq
skipbytes   0
ulxmap  -179.996
ulymap  89.996
xdim    1
ydim    1

to perform a simple gdal translation with:

gdal_translate -a_srs "+proj=latlong +r=6370997" -a_ullr -179.996 89.996 179.996 -89.996 goge2.bsq destfile.tif

to get the data into a GIS compatible format:

enter image description here

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