Erosion Algorithm

I read an article about some researchers who were trying to simulate erosion numerically a few years ago and I was somewhat disappointed by the purely random appearance of the terrains I was creating at the time so I wrote my own program for simulating erosion using Python.  This requires that you have python and PIL (Python Imaging Library) installed on your system.

The following two images illustrate before and after erosion is applied to the height map.

This results in decent erosion but the algorithm produces some sharp edges so I usually load the file into photoshop and give it some blur and adjust the contrast before rendering it.

from PIL import Image

from random import *

def erode(n=200000,nl=50,ev=.25,maxx=319,maxy=239):

    im = Image.open("gray_terrain01.png")

    

    for k in range(n):

        cx = int(uniform(1,maxx-1))

        cy = int(uniform(1,maxy-1))

        for l in range(nl):

            cv,cv,cv = im.getpixel((cx,cy))

            mini = cx

            minj = cy

            minv = cv

            #print "cent",cv

            for i in range(3):

                for j in range(3):

                    iv,iv,iv = im.getpixel((cx+i-1,cy+j-1))

                    #print iv

                    if (iv<minv):

                        mini = cx+i-1

                        minj = cy+j-1

                        minv = iv

            #print "min",mini,minj

            if (minv<cv):

                hard = (256.0-cv)/256.0

                erod_val = ev*hard

                iv = int(minv + (cv-minv)*erod_val)

                cv = int(cv - (cv-minv)*erod_val)

                #print "down",cv,

                #print "up",iv

                x = cv,cv,cv,

                y = iv,iv,iv,

                im.putpixel((cx,cy),x)

                im.putpixel((mini,minj),y)

                cx=mini

                cy=minj

            else:

                break

            if cx <= 0:

                break

            if cy <= 0:

                break

            if cx >= maxx-1:

                break

            if cy >= maxy-1:

                break

    

    im.save("eroded.png")

erode()