Regional modeling of outlet glaciers using PISM requires isolating a drainage basin.

Our goal was to develop a tool using surface topography to divide an ice sheet into smaller basins without using measured ice surface speed (which may not be available in some cases).

Please see doc/method.tex for details (unfinished).

The C code that does the heavy lifting uses an ODE solver from GSL, although hand-coding one of stanadard time-stepping methods would probably result in code that performs about as well.

This code can be used separately (i.e. in a C-only program).

In addition to GSL, some functions are parallelized using OpenMP, so a compiler supporting OpenMP 2.5 or later is needed (GCC 4.2 and later is OK.)

Cython is used to make the C code mentioned above available from Python.

The wrapper script pism_regional.py uses sevaral Python modules, notably

• netcdf4-python for NetCDF I/O
• NumPy for 2D arrays, etc
• matplotlib for plotting
• Tkinter for the GUI

All these libraries and packages are available via a package manager on Linux systems.

To install for the current user, run

python setup.py install --user

To build and use from the current directory, run

python setup.py build_ext --inplace

To disable OpenMP, run

NO_OPENMP=1 python setup.py ...

If you have GSL in a non-standard location, run

GSL_PREFIX=/path/to/gsl python setup.py ...

On systems where the default compiler does not support OpenMP you can specity the compiler to use like this:

CC=gcc-4.2 CXX=g++-4.2 python setup.py ...

• Run pism_regional.py. Select a NetCDF file containing variables x, y, usurf, and thk. 2D arrays have to be stored in the (y,x) order.
• Select the terminus region using the mouse.
• Click "Compute the drainage basin mask"
• Save the mask to a file.
• Quit the scrip by closing all windows.

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