Blue Marble

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Revision as of 22:29, 29 September 2008 by HamishBowman (talk | contribs) (2002: fix)

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The classic Blue_Marble photo of Earth was taken by crew of Apollo 17 on their way to the moon in 1972.

In 2002 NASA released an updated version suitable for GIS created by a mosaic of satellite images with the clouds removed. In 2005 this was rereleased, with a separate image provided for each month of the year.


This page deals with importing the latter into GRASS.

2002

The entire image is 43200x21600, 1/2 arc-minute (~1km per pixel) resolution.

Download

To download the maps you have a few choices:

  • The new maps can be found here:

21600x21600 East Hemisphere (401mb)

[1]

21600x21600 West Hemisphere (241mb)

[2]

The Wget program is nice for downloading these. For example:

 wget ftp://veftp.gsfc.nasa.gov/bluemarble/land_shallow_topo_east.tif
 wget ftp://veftp.gsfc.nasa.gov/bluemarble/land_shallow_topo_west.tif


  • From the original site (only gzip compressed)

Goto [3]

If you are west, download

MOD09A1.W.interpol.cyl.retouched.topo.3x21600x21600.gz

if you are east, download

MOD09A1.E.interpol.cyl.retouched.topo.3x21600x21600.gz

If you are in England or West Europe, you will need both files, because they have to overlap.


  • Download them via ED2k Link (bzip2 compressed):
ed2k://|file|top_nasamap_east.raw.bz2|379972653|7312437945bd47ccf0b2a0c3452d5836|/
ed2k://|file|top_nasamap_west.raw.bz2|226307352|13ab6e8a6e014fa23bb83db25855bb71|/

This files have a uncompressed size of 1.4GB each and are in raw RGB format. The bzip2 compressed files are 363MB (east) and 216MB (west) in size.


  • Check if the files are available from geotorrent.org
[4]


Import

  • Create a lat/lon location. I used WGS84 as the datum, but as typical datum differences are much less than the pixel resolution I'm not sure if it makes a difference which one you chose. The only problematic choice might be sphere (the GDAL "null nadgrids" problem). You can overlay a world coastline, like admin98.shp, to test how you've done.
  • Create "world files" for the raw .tif images (thus making them into GeoTiffs)
land_shallow_topo_east.wld
0.008333333333333
0.000000000000000
0.000000000000000
-0.008333333333333
0.00416666666666665
89.99583333333334
land_shallow_topo_west.wld
0.008333333333333
0.000000000000000
0.000000000000000
-0.008333333333333
-179.9958333333333
89.99583333333334


  • Import into a lat/lon location with r.in.gdal
This will create three images, one for red, green, and blue.
  • Zoom to the extents of both images (or just one) with:
 g.region rast=BlueMarble_2002_east,BlueMarble_2002_west
  • Merge east and west images by color bands with r.patch
  • If you wish to combine R,G,B bands into a single raster map do so with r.composite. Only do this if you must, as you'll lose detail.

Issues

  • I've had good results exported at natural resolution, and then cubic rescale in the [[5]] to my desired size.
  • Some of the pixels are NULL. If any of the R,G,B map pixels are NULL, d.rgb will show white for that cell, which may stick out badly. To mitigate the problem, try erasing the display to black first with d.erase.

2005 monthly