Flocking 3D Alternate

Flocking 3D Alternate preview image

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Uri_dolphin3 Uri Wilensky (Author)



Tagged by Reuven M. Lerner about 7 years ago

Model group CCL | Visible to everyone | Changeable by group members (CCL)
Model was written in NetLogo 3D 4.1pre7 • Viewed 506 times • Downloaded 38 times • Run 0 times
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This is a vector-based 3D flocking model, based on Jon Klein's implementation of Craig Reynolds' Boids algorithm. Each bird is influenced by a series of urges. By assigning different weights to each urge, the birds exhibit different flocking behaviors.


Each bird has vectors for velocity and acceleration, that is, a velocity and acceleration in the x, y, and z directions. Each of these vectors is influenced by six urges, to be near the center of the flock, to have the same velocity as the rest of the flock, to be keep spacing correct, to avoid colliding with obstacles, to be near to the center of the world and to wander throughout the world. Each of these factors affects the resulting velocity and acceleration; however, the sliders in the interface weight the amount that each has an effect.


Choose the number of birds with the POPULATION slider. Press SETUP to create the birds. Press GO to start the simulation.

BUILD-CUBES randomly places floating-ball obstacles throughout the world. BUILD-WALL creates a randomly placed wall.

VISION is the distance that a bird can see around it. MAX-VELOCITY is the fastest a bird can go and MAX-ACCELERATION is the fastest a bird can accelerate. CRUISE-DISTANCE is the minimum distance from a nearby bird for a bird to feel comfortable.

A bird's movement is determined by the set of urges acting on that bird:

CENTER-CONSTANT - urge to move towards the center of its flock

VELOCITY-CONSTANT - urge to align its velocity with the velocity of her flockmates

SPACING-CONSTANT - urge to be no closer than CRUISE-DISTANCE from other birds

AVOIDANCE-CONSTANT - urge to avoid colliding with obstacles

WORLD-CENTER-CONSTANT - urge to avoid the edges of the world

WANDER-CONSTANT - urge to move in a random way

The urge-constant sliders control the weight of each urge in determining the birds' behavior.

If the VERTICAL-SPACING? switch is off the spacing urge only operates horizontally.

If a bird hits an obstacle, the bird dies. The COUNT DEAD-BIRDS monitor shows the number of dead birds.


Compare how long it takes the birds to form flocks in this model to how long it takes in the regular 3D Flocking model.

Given the default settings the flocks travel in a circular pattern.


Turn VERTICAL-SPACING? off and notice how it changes the shape of the flocks.

Try changing the different constants so that the birds become better or worse at avoiding obstacles.


Try adding different urges to the model; also try making different types of obstacles for birds to avoid.

Create different breeds of birds that behave differently from each other and see how they interact.


This model uses lists and map fairly extensively to represent and manipulate vectors.


This model is based on Jon Klein's "Swarm" demo for breve, (see http://www.spiderland.org/breve/) which was inspired by Craig Reynolds classic Boids flocking algorithm.


If you mention this model in an academic publication, we ask that you include these citations for the model itself and for the NetLogo software:

- Wilensky, U. (2005). NetLogo Flocking 3D Alternate model. http://ccl.northwestern.edu/netlogo/models/Flocking3DAlternate. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

- Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

In other publications, please use:

- Copyright 2005 Uri Wilensky. All rights reserved. See http://ccl.northwestern.edu/netlogo/models/Flocking3DAlternate for terms of use.


Copyright 2005 Uri Wilensky. All rights reserved.

Permission to use, modify or redistribute this model is hereby granted, provided that both of the following requirements are followed:

a) this copyright notice is included.

b) this model will not be redistributed for profit without permission from Uri Wilensky. Contact Uri Wilensky for appropriate licenses for redistribution for profit.

Comments and Questions

Click to Run Model

breed [ birds bird ]
breed [ dead-birds dead-bird ]

birds-own [
  flockmates         ;; agentset of nearby turtles
  nearest-neighbor   ;; closest one of our flockmates
  velocity           ;; vector with x y and z components it is determined by the previous velocity
                     ;; and the current acceleration at each step
  acceleration       ;; vector with x y and z components, determined by the six urges

;; Setup Procedures

to setup
  setxyz 0 -30 0
  create-birds population
      set size 0.75
      set velocity [ 0 0 0 ]
      set acceleration [ 0 0 0 ]
      set color yellow + 2 - random-float 6
  ask turtle 0 [ set color red ]

  ;; checkered floor
  ask patches
    with [ pzcor = min-pzcor ]
      [ set pcolor 3 + green + ( pxcor + pycor ) mod 2 ]

to place-bird ;; turtle procedure
  setxyz random-xcor random-ycor random-zcor
  ;; make sure that the birds are not on the floor or inside the
  ;; any obstacles that have been created.
  while [ pcolor != black ]
  [ setxyz random-xcor random-ycor random-zcor ]

;; Runtime Procedures

to go
  ask birds
  [ flock
    ;; if we've hit something
    ;; we're a goner
    if pcolor != black
    [ hatch-dead-birds 1
      [ bk 1 ]
      die ]
  ;; ask the dead ones to continue falling
  ask dead-birds
    [ fall ]

to flock  ;; bird procedure
  ;; look for birds in my vicinity

  ;; acceleration at each step is determined
  ;; entirely by the urges
  set acceleration (list 0 0 0)

  add-urge world-center-urge world-center-constant
  add-urge wander-urge wander-constant
  add-urge avoid-obstacle-urge avoidance-constant

  ;; if I'm not in a flock ignore the flock related
  ;; urges
  if count flockmates > 0
  [ add-urge spacing-urge spacing-constant
    add-urge center-urge center-constant
    add-urge velocity-urge velocity-constant ]

  ;; keep the acceleration within the accepted range
  if magnitude acceleration > max-acceleration
  [ set acceleration
        normalize acceleration) ]

  ;; the new velocity of the bird is sum of the acceleration
  ;; and the old velocity.
  set velocity (add velocity acceleration)

  ;; keep the velocity within the accepted range
  if magnitude velocity > max-velocity
  [ set velocity
        normalize velocity) ]

  let nxcor xcor + ( item 0 velocity )
  let nycor ycor + ( item 1 velocity )
  let nzcor zcor + ( item 2 velocity )
  facexyz nxcor nycor nzcor
  fd 0.1 * magnitude velocity

to add-urge [urge factor] ;; bird procedure
  set acceleration add acceleration scale factor normalize urge

to-report world-center-urge  ;; bird reporter
  ifelse distancexyz 0 0 0 > 10
  [ report (list (- xcor) (- ycor) (- zcor) ) ]
  [ report (list 0 0 0) ]

to-report center-urge ;; bird reporter
  ;; report the average distance from my flockmates
  ;; in each direction
  if count flockmates = 0 or center-constant = 0
  [ report (list 0 0 0) ]
      [ ?2 - ?1 ]
      (list xcor ycor zcor)
        mean [ xcor ] of flockmates
        mean [ ycor ] of flockmates
        mean [ zcor ] of flockmates ) )

to-report velocity-urge ;; bird reporter
  ;; report the average difference in velocity
  ;; from my flock mates
  if count flockmates = 0 or velocity-constant = 0
  [ report (list 0 0 0) ]
    ( map
      [ ?1 - ?2 ]
        mean [ item 0 velocity ] of flockmates
        mean [ item 1 velocity ] of flockmates
        mean [ item 2 velocity ] of flockmates )
      velocity )

to-report wander-urge ;; turtle reporter
  ;; report 3 random numbers between -1 and 1
  report n-values 3 [ (random-float 2) - 1 ]

to-report spacing-urge ;; turtle reporter
  let urge [ 0 0 0 ]
  ;; report the sum of the distances to birds
  ;; in my flock that are closer to me than
  ;; cruise-distance
  ask flockmates with [ distance myself < cruise-distance ] [
    set urge
          (list [xcor] of myself [ycor] of myself [zcor] of myself)
          (list xcor ycor zcor))
  ;; when vertical spacing is not on ignore the
  ;; z component of the spacing urge.
  if not vertical-spacing? [ set urge lput 0 but-last urge ]
  report urge

to-report avoid-obstacle-urge ;; turtle reporter
  let urge (list 0 0 0)
  if avoidance-constant = 0 [ report urge ]
  ;; report the sum of the distances from
  ;; any patches that are obstacles
  ;; in each direction
  ask patches in-radius vision with [ pcolor != black ]
  [ set urge
          (list [xcor] of myself [ycor] of myself [zcor] of myself)
          (list pxcor pycor pzcor)
  report urge

to find-flockmates  ;; turtle reporter
  ;; latch on to the nearby birds
  set flockmates other birds in-radius vision

to fall ;; dead-bird procedure
  if zcor > min-pzcor + 1
    [ set zcor zcor - 0.5 ]

;; world building

to build-cubes
  ask n-of 20 patches
  [ set pcolor blue + random 3
    ask neighbors [ set pcolor blue + random 3 ] ]

to build-wall
  let x max-pxcor - random world-width
  let ydir 1 - random 2
  if ydir = 0 [ set ydir -1 ]
  let height random max-pxcor
  ask patches
    with [ pxcor = x and ydir * pycor < 0 and pzcor < height ]
    [ set pcolor gray + random 2 ]

;; vector operations

to-report add [ v1 v2 ]
  report (map [ ?1 + ?2 ] v1 v2)

to-report subtract [ v1 v2 ]
  report (map [ ?1 - ?2 ] v1 v2)

to-report scale [ scalar vector ]
  report map [ scalar * ? ] vector

to-report magnitude [ vector ]
  report sqrt sum map [ ? * ? ] vector

to-report normalize [ vector ]
  let m magnitude vector
  if m = 0 [ report vector ]
  report map [ ? / m ] vector

; Copyright 2005 Uri Wilensky. All rights reserved.
; The full copyright notice is in the Information tab.

There are 3 versions of this model.

Uploaded by When Description Download
Uri Wilensky about 10 years ago Updated from NetLogo 4.1 Download this version
Uri Wilensky about 10 years ago Model from NetLogo distribution Download this version
Uri Wilensky about 10 years ago Flocking 3D Alternate Download this version

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