Lakewalker is a tool that automatically traces lakes and other bodies of water from Landsat data.

It can be used to trace almost any land/water interface, including:
  - lakes
  - islands
  - large rivers
  - coastlines

Lakewalker requires Python and the Python Imaging Library (available from http://www.pythonware.com/products/pil/).

A full list of options is available by running "./lakewalker.py --help".

QUICK START:

To trace a single lake, picking a point inside the lake and use the
--lat and --lon command-line parameters:
  ./lakewalker.py --lat 51.2 --lon -99.8

NOTE: By defualt, the algorithm starts by going to the specified start
point and travelling due east until it hits land. So, to trace an
island, place the start point in the water to the west of the
island. This can be modified with the --startdir option.

The output will be placed in a file named lake.osm. This can be
changed by using the -o or --out switch. The OSM file can then be
opened in JOSM and uploaded to OSM. It is HIGHLY RECOMMENDED that you
use the JOSM WMS plugin to visually confirm that the data makes sense
before you upload it.

If it doesn't work, the most likely problem is the threshold value
used to differentiate between land and water. Try tweaking the
--threshold parameter; you can either experiment blindly, or open the
downloading Landsat tiles in an image editor and check the gray
values.

To trace a lot of lakes, create a .osm file containing untagged nodes,
and no segments or ways. Then, use the -i or --in command-line
parameter:
  ./lakewalker.py -i start_points.osm

There are a large number of other command-line options which need to
be documented yet. Short documentation is available with --help;
longer documentation does not (yet) exist.

ABOUT THE TILE CACHE

The lake walker downloads imagery from NASA's Landsat WMS server. This
imagery is cached locally as PNG files, named
landsat_*_*_xy_*_*.png. Whenever imagery is needed, the local cache is
checked first, so that multiple runs in the same area do not
continually request the same data from NASA. These files can be
deleted without causing problems; they will simply be re-downloaded if
they are ever needed again.