Intelligent Agent #2
(ninja turtles)

As promised, here is a super simple example of an Intelligent Agent program using NetLogo.

The goal is to find the boundaries within an image. There are powerful algorithms for locating boundaries, but I wanted to do it another way, I wanted to see if Intelligent Agents could be used. As I said in my earlier post, NetLogo provides a rapid prototyping means for creating Agents and offers a visual development and execution environment. Below is the image I started with. Note the low resolution. NetLogo could handle a much higher resolution image, but the image would be too large to fit in this post, so I had to lower the resolution so I could display it here. (now someone who is an expert in NetLogo might point me to a setting to make the ‘patches’ smaller, that would help).

Screen shot before Agent run.

Screen shot after Agents have run a bit.

As you can see, the Agents did a fair job of locating the color contours, and thus the edges.
My approach is bone headed simple. Agents wander around randomly keeping track of the color of recently visited patches. If the new patch is enough different from the prior patch, then it marks the patch White to indicate a boundary.
The approach has a serious flaw, and a weakness. The flaw is that the boundary is dependent on the direction of the Agent at the time it encounters a boundary. For example, an Agent moving from Blue to Red will mark the Red patch, while a neighboring Agent moving from Red to Blue will mark the Blue patch. This causes the edge to be much more ragged than it really is. This could be solved by adding a rule such as always mark the lighter colored patch.
The weakness is the algorithm could be much more efficient. Rather than wander aimlessly, the Agent could try to determine the direction of the edge and follow it. If two Agents collide, one could jump to a new location to let the other complete the boundary.

I am sure you are eager to see some code. OK, here goes:
extensions [bitmap ]

turtles-own [last-color second-last-color hunt-color]

to setup
let img bitmap:import "C:\\Temp\\Desert.jpg"
;;set img bitmap:to-grayscale img
bitmap:copy-to-pcolors img false

create-turtles 10 [fd 10]
ask turtles [
set last-color pcolor
set second-last-color pcolor
set hunt-color pcolor

to hunt
ask turtles[
rt random 50
lt random 50
fd 1
if pcolor = 0
set second-last-color last-color
set last-color pcolor
if isContour second-last-color last-color
[set pcolor [255 255 255]]


to-report isContour [color1 color2]
let retVal false
foreach [0 1 2]
;; show item ?1 color1
if abs (item ?1 color1 - item ?1 color2) > 60 ;; or item ?1 color2 - item ?1 color1 > 60
[set retVal true]
if approximate-rgb item 0 color1 item 1 color1 item 2 color1 = white or approximate-rgb item 0 color2 item 1 color2 item 2 color2 = white
[set retVal false]
report retVal

to jump-elsewhere
set xcor random 40
set ycor random 40
set last-color pcolor
set second-last-color pcolor
set hunt-color pcolor

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