On 10/28/2010 07:56 PM, A. Marcia BARBOSA wrote:
Dear lists,
I need to import the map available here
(http://geodata.grid.unep.ch/mod_download/download_geospatial.php?selectedID=2150&newFile=download/Nightlights_2003_tif.zip)
to GRASS. The map is in Tiff format and appears fine in QGIS, but when
I import it to GRASS (with r.in.gdal) it becomes a very narrow N-S
stripe.
Here's the raster info that QGIS gives me on this map:
I think I know what the problem is. Have a look at the bounds below:
Corner Coordinates:
Upper Left (-180.0041667, 65.0041667) (180d 0'15.00"W, 65d 0'15.00"N)
Lower Left (-180.0041667, -65.0041661) (180d 0'15.00"W, 65d 0'15.00"S)
Upper Right ( 180.0041652, 65.0041667) (180d 0'14.99"E, 65d 0'15.00"N)
Lower Right ( 180.0041652, -65.0041661) (180d 0'14.99"E, 65d 0'15.00"S)
The left (W) extent goes beyond -180 and the right (E) also goes beyond
+180. So the image has "fallen off the edge" ;-)
If I check with gdalinfo on the original tiff, before importing into
GRASS, here's what I see:
mi...@hayun-820:~/Download$ gdalinfo Nightlights_2003.tif
Driver: GTiff/GeoTIFF
Size is 43201, 15601
... more lines ...
Pixel Size = (0.008333330042660,-0.008333330042660)
... more metadata ...
Corner Coordinates:
Upper Left (-180.0000000, 65.0000000) (180d 0'0.00"W, 65d 0'0.00"N)
Lower Left (-180.0000000, -65.0082820) (180d 0'0.00"W, 65d 0'29.82"S)
Upper Right ( 180.0081912, 65.0000000) (180d 0'29.49"E, 65d 0'0.00"N)
Lower Right ( 180.0081912, -65.0082820) (180d 0'29.49"E, 65d 0'29.82"S)
Center ( 0.0040956, -0.0041410) ( 0d 0'14.74"E, 0d 0'14.91"S)
Here again the Right side is > 180. So, in import to GRASS, it gets
"wrapped" to the west, and the end result is, like above, a very narrow
raster with E-W extent 0.0000015 degrees.
One way to work this out is to clip the original raster slightly before
importing. The gdal tool gdal_translate does this with the -projwin
option like:
gdal_translate -projwin -179.99 65 179.99 -65 Nightlights_2003.tif
Nightlights_2003clip.tif
Here, I've shaved off a bit on the E and W so it fits into the -180 to
180 bounds. Now if I redo r.in.gdal using the clipped raster, it appears
correctly in GRASS.
--
Micha
Thanks for any help,
Márcia
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--
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
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