               Synthetic Fluvial Erosion 

The "erode" program takes as a minimum input a filename, which should be
in the "mat" Matlab floating-point binary format. (although, actually, I  
think ascii PGM works also; I don't remember!) Gforge can generate this
format, or you can use the "hcon" heightfield-format-conversion utility.
The optional parameters control erosion rates, check the *.bat files
for examples which generate an erosion animation.  Gforge always generates
square arrays, but hcon and erode can handle non-square arrays.

erode has a bug which generally doesn't show up on heightfields created by
'gforge' (mostly what I've used), but may on other data: if there is
a part of the surface perfectly flat, it may bomb.

also, sometimes there's some kind of instability where there is suddently 
a spike pushing up out of the surface like a new volcano or something; this
seems to happen at the higher erosion or smoothing rates. It might not
appear with the default values. Then again it might.

erode writes out intermediate files as it works so that if you get impatient
and stop it as it's running, you can see some results anyway. Three
output files give you eroded topology, an image of the river system, and a 
"delta" file showing you what's been added/subtracted from the topology
in this run. The delta.mat file typically contains very small numbers 
so you should use the -rescale option to hcon when converting to a gif.

----- <legal stuff> -----------------

This version of "erode" is pre-alpha code and NOT for general release.
Erode is Copyright (C) 1995 John P. Beale   <beale@jump.stanford.edu>

I have used Tom Boutell's gd (gifdraw) library for GIF I/O, which requires 
the following notices. GD is

        Written by Tom Boutell, 5/94.
        Copyright 1994, Cold Spring Harbor Labs.
        Permission granted to use this code in any fashion provided
        that this notice is retained and any alterations are
        labeled as such. It is requested, but not required, that
        you share extensions to this module with us so that we
        can incorporate them into new versions. 

        Tom Boutell, boutell@netcom.com
        http://sunsite.unc.edu/boutell/index.html
        116 14th Ave E Apt 2
        Seattle, WA 98102
-------------

The GIF encoder used in GD contains the following additional notices:

   Code drawn from ppmtogif.c, from the pbmplus package
   Based on GIFENCOD by David Rowley <mgardi@watdscu.waterloo.edu>. A
   Lempel-Zim compression based on "compress".
   Modified by Marcel Wijkstra <wijkstra@fwi.uva.nl>
   
   Copyright (C) 1989 by Jef Poskanzer.
   
   Permission to use, copy, modify, and distribute this software and its
   documentation for any purpose and without fee is hereby granted, provided
   that the above copyright notice appear in all copies and that both that
   copyright notice and this permission notice appear in supporting
   documentation.  This software is provided "as is" without express or
   implied warranty.
   
   The Graphics Interchange Format(c) is the Copyright property of
   CompuServe Incorporated.  GIF(sm) is a Service Mark property of
   CompuServe Incorporated.

/* +-------------------------------------------------------------------+ */
/* | Copyright 1990, 1991, 1993, David Koblas.  (koblas@netcom.com)    | */
/* |   Permission to use, copy, modify, and distribute this software   | */
/* |   and its documentation for any purpose and without fee is hereby | */
/* |   granted, provided that the above copyright notice appear in all | */
/* |   copies and that both that copyright notice and this permission  | */
/* |   notice appear in supporting documentation.  This software is    | */
/* |   provided "as is" without express or implied warranty.           | */
/* +-------------------------------------------------------------------+ */
                                                    
