===========================================================================

To provide map projections support your first need to make sure the libproj4
library is installed.  The source code for this can be found at:

http://home.comcast.net/~gevenden56/proj/
(http://home.comcast.net/~gevenden56/proj/libproj4.3_20081120.tar.bz2)

The "--with-libproj4=DIR" switch in configure can be used give the location
of this library.


The following additional PRO files must be acquired and placed in the
appropriate directories:

map_grid.pro
map_horizon.pro
map_image.pro
map_patch.pro
map_point_valid.pro
map_proj_image.pro
map_proj_info.pro
map_proj_init_commonblock.pro
map_proj_init_common.pro
map_proj_init.pro
map_set.pro
map_struct_append.pro

These files can be found by entering the following URL into your web
browser:

http://idlastro.gsfc.nasa.gov/cgi-bin/idllibsrch?keyword=map_

clicking on the appropriate file and saving it to your computer.

They can be placed in any directory within you GDL path.

===========================================================================

MAP_CONTINENTS is implemented in GDL using the GSHHS (Global 
Self-consistent, Hierarchical, High-resolution Shoreline Database) 
available under the GNU GPL. To provide support for MAP_CONTINENTS the 
database files and one header file (gshhs.h) need to be downloaded e.g. from:

ftp://ftp.soest.hawaii.edu/pwessel/gshhs

The header file for the 2.0 dataset is in the gshhs_1.12_src.zip file.
The datafiles (*.b) are in the gshhs_2.0.tbz file.

When compiling GDL, the --with-gshhs option must be given (not enabled 
by default), optionally with an argument pointing to the GSHHS installation
prefix:

--with-gshhs : searches gshhs.h in the default include path of the compiler
--with-gshhs=/usr/local : searches for /usr/local/include/gshhs.h

GDL searches for the GSHHS datafiles (gshhs_f.b, gshhs_l.b, etc...) in the
$GDLDATADIR/../gshhs/ directory (we need a better solution - FIXME!)

Reference:
Wessel, P. and Smith, W.H.F., 1996. A global, self-consistent, hierarchical, 
  high-resolution shoreline database. J. Geophys. Res., 101(B4): 8741--8743.

===========================================================================

The following projections are at least partially supported
(numbers defined in the map_sep.pro file itself):

Stereographic Projection:  (1)
Orthographic Projection:   (2)
Lambert Conformal Conic:   (3)
Lambert Equal Area Conic:  (4)
Gnomonic:                  (5)
Azimuthal Equidistant:     (6)
Satellite:                 (7) (add 28/07/2008)
Cylindrical Equidistant:   (8)
Mercator:                  (9)
Aitoff:                   (12)
Robinson:                 (17) (add 28/07/2008)

NOTE: Map projection support in GDL is a work in progress.  There are
BUGS!!  These will be fixed as time permits.  Additional projections
will also be added in the same manner.  Bug reports and projection
requests are appreciated.

Joel Gales


PS (by AC): a demo ("test_map.pro") is now available in the testsuite/.
If not in the PATH, you must provide the root of the path to the database files
(if file "plow.dat" is here /opt/GDL/lib_GDL_0.9/resource/maps/low/plow.dat
--> you must provide /opt/GDL/lib_GDL_0.9/ to "test_map"
or you can call it via "test_map, dir='/opt/GDL/lib_GDL_0.9/')
This demo has been succesfully tested on Linux x86_32 and x86_64. 
Please reports BUG with as simple as possible code giving it !

