CODEWITHSUNDEEP
netlogo
607
607

Reputation: 35

Netlogo 'towards' behaviour

For a pursuit-evasion assignment I need to use the NetLogo command 'towards', but it doesn't seem to work, or I don't understand it.
What I think it should do: give the angle between the heading of the turtle and the line connecting the turtle with the target.
Here's the code for a simple model I made just to show the problem.

to set-up
  clear-all
  create-turtles 2
  ask turtle 0 [
    set xcor 0
    set ycor 0
    set shape "circle"
  ]
  ask turtle 1 [
    set xcor min-pxcor
    set ycor max-pycor
    set heading 135
  ]
end

to go
  ask turtle 0 [ fd 0.1 ]
  ask turtle 1 [ show towards turtle 0 ]
end

And here's a video of the behaviour. https://youtu.be/MUBiAypppc4 (I couldn't find a way to remove the audio without just replacing it using YouTube's current editing system, I'm sorry; you'll have to mute the audio yourself)
Examples of expected behaviour:
from 0:14 to 0:19, I would expect the number to gradually decrease, not increase
at about 0:38, I would expect the number to be 0, not somewhere around 300
between 0:38 and 0:42, I would expect the number to decrease or increase consistently, without those two sudden jumps

Is there a problem somewhere, or does 'towards' mean something different than I thought?

Upvotes: 1

Views: 134

Answers (1)

JenB
JenB

Reputation: 17678

So turtle 0 is moving and turtle 1 is reporting the direction to turtle 0. I think towards is working fine but you have forgotten about the world settings. For example, in the 14-19s part, the shortest path from 0 to 1 is down and left (about 220 heading), but that shortest path is with the world wrapped. Your turtles can move off one side and come in on the other (as you can see turtle 1 doing).

NetLogo measures distances and directions taking into account the wrapping configuration. It knows that the shortest path to get from turtle 0 to turtle 1 goes off the side and comes in the other, and reports the direction that the turtle would have to move to follow that path.

Create a link and you can see this. Revised code:

to set-up
  clear-all
  create-turtles 2
  ask turtle 0 [
    set xcor 0
    set ycor 0
    set shape "circle"
  ]
  ask turtle 1 [
    set xcor min-pxcor
    set ycor max-pycor
    set heading 135
    create-link-with turtle 0
  ]
end

to go
  ask turtle 0 [ fd 0.1 ]
  ask turtle 1 [ show towards turtle 0 ]
end

Upvotes: 2

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