er1u.tar.gz
er1u.zip

               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 HF-Lab and save the image using a xxx.mat filename.

The optional parameters control erosion rates, check the *.bat files
for examples which generate an erosion animation.  Gforge always generates
square arrays, but 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 load it into HF-Lab and renormalize it ('norm 0 1') before
saving it to a GIF and viewing.

WARNING: 'Erode' is alpha code; you may well run into a bug. Don't count
on it to do anything useful, in fact. But, I'm making it available for the
brave and for those with time on their hands, to see if they can coax some
interesting results out of it.

John Beale
beale@best.com
----------------------

Reference:                                      

Ken Musgrave published on synthetic fluvial erosion in 1989, see

Musgrave, F.K., C.E. Kolb, and R.S. Mace, 
The Synthesis and Rendering of Eroded Fractal Terrains, 
Computer Graphics, July, 1989, 23:3, pp. 41-50.
http://portal.acm.org/citation.cfm?id=74337

Ken also mentions the subject in his 1993 thesis, 
for example see page 58 in  
http://www.kenmusgrave.com/dissertation.pdf