3/19/07  - D. Sandwell

The programs and scripts in this directory provide a way to extract
data from the global topography and gravity grids.  There are two
ways the data can be extracted.

img2xyz    -  Extract data in rectangular area with an output format
              ASCII lon, lat, topo.

interp_ship - Extract data at lon, lat points provided by the user.
              A bilinear interpolation is used and a new column is 
              added to the user's file.

update_grid - This script used GMT commands along with the above
              programs img2xyz and interp_ship to merge new topography
              measurements with the global topogrid.  The new topography
              is provided as an ASCII xyz file.  The output file is a GMT 
              grid at of the area and spacing requested by the user.

Note if you do not have GMT running on your computer you can install it
free but it is a lot of work.  The programs img2xyz and interp_ship
are self-contained Fortran and C. If you are on an Intel computer you will
need to swap the bytes of the global topography grid.   Do a man on dd.
Here is an example.

dd if=global_file.img of=global_file_intel.img bs=21600 conv=swab

12/6/04
To compoile and link on other platforms edit the file diskio.c and make
the change to the desired system: osx, linux, hp, or sun.