/*! \page globe How to import GLOBE DEM data with gdal/FortranGIS

A popular DEM (Digital Elevation Model) raster dataset available on
the internet is the Global Land One-kilometer Base Elevation from
NOAA, known as GLOBE
http://www.ngdc.noaa.gov/mgg/topo/globe.html. This dataset comes split
into tiles which can be seen by gdal as a unique dataset, only after
applying some nonobvious tricks. This page explains how to access the
GLOBE dataset from gdal in general, it is not specific to FortranGIS,
but of course all the information applies to FortranGIS too.

\section georeference Georeferencing the tiles

The 16 raw tiles covering the whole Earth and available for download
from NOAA site contain no information about their geographical
positioning. However, browsing the GLOBE site, you can get to this page
http://www.ngdc.noaa.gov/mgg/topo/elev/esri/hdr/ from which you can
download the ESRI header files associated to the raw tiles.

So, after having downloaded the tiles, which have an austere \c ?10g
naming scheme, the next step is to download the corresponding header
files \c ?10g.hdr and to save them in the same directory where the raw
tiles are kept. Unfortunately, gdal interprets this dataset as
composed of unsigned integers, thus it misrepresents the points below
sea level and the no-data values (=-500) on sea. To improve this
situation, you should hand-edit the .hdr files adding a line like the
following:

\code
PIXELTYPE       SIGNEDINT
\endcode

At this point you can check whether gdal can correctly reference the
single tiles by executing:

\code
gdalinfo -stats n10g
\endcode

assuming that the files \c n10g.hdr and \c n10g are available in the
current directory.

\section stick Sticking the tiles together

In order to let gdal see all the tiles as an unique dataset, you can
build a so-called gdal virtual raster dataset, which consists of a
metafile in xml format understood by gdal, describing one or more
external datasets in a format known by gdal, without duplicating the
data, see also http://www.gdal.org/gdal_vrttut.html for a complete
description. For this purpose you need to have gdal version 1.6.1 or
newer, having the \c gdalbuildvrt command, and you should simply
execute:

\code
gdalbuildvrt globe.vrt ?10g
\endcode

If the execution is successful, when you will point gdal to the \c
globe.vrt dataset it will see a truly global set of data, hiding the
details of accessing the correct tiles according to the area you
request. 

*/