This package downloads DFSG-free [0] elevation datasets and converts
them to geotiff [1] files.

At the moment the following datasets are processed:

- Shuttle Radar Topography Mission (SRTM) Version 2.1 [2] digital
terrain elevation data (DTED) at 1 and 3 arc-seconds resolution

- Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) mean
  layers at 7.5 arc-seconds and 30 arc-seconds.
  (You really should read [3] for GMTED2010 details, unfortunately it
  seems like this report is not freely redistributable and can't be
  included in this package).

Important notes:

- GMTED2010 7.5 arc-seconds mean layer:
  data is slightly modified (the original data is missing Greenland
  but doesn't mark it as nodata - the Makefile does that)

Misc notes:

- the produced geotiffs use internal tiles, lzw-compression and
  include overviews

- no data for 83d59'59.50"N to 90N (arctic ice / water)

- earlier versions of this package combined those datasets into one by
  upsampling GMTED2010 data to 3 arc-seconds, but I think that is a
  bad idea.  It is better to delay upsampling as long as possible. For
  an example how to combine the datasets on-the-fly you might wish to
  take a look at [5]

References:

[0] http://en.wikipedia.org/wiki/DFSG

[1] http://en.wikipedia.org/wiki/GeoTIFF

[2] http://dds.cr.usgs.gov/srtm/version2_1/Documentation/

[3] Danielson, J.J., and Gesch, D.B., 2011, Global multi-resolution
    terrain elevation data 2010 (GMTED2010): U.S. Geological Survey
    Open-File Report 2011–1073, 26p.
    http://pubs.usgs.gov/of/2011/1073/pdf/of2011-1073.pdf

[4] http://karme.de/freedem/data/freedem_remote.vrt

[5] http://karme.de/elpro/
