globals [w ; width (in degrees) of blind spot behind bird obstacles_opaque? ; whether or not a bird is unaware of neighbors ; that are hidden behind obstacles screen-half-width ; one half of world-width screen-half-height] ; one half of world-height turtles-own [neighbor_1 neighbor_2 neighbor_3 ; ID number of closest neighbors distance_1 distance_2 distance_3 ; distance to closest neighbors target_1 target_2 target_3 ; preferred heading considering each neighbor -alone- target ; preferred heading considering all three neighbors i ; counter for selecting neighbors dist ; distance from a bird to the one in question acceleration ; extra distance to move forward in a time step vis_x ; x-counter when testing for obstacles vis_y ; y-counter when testing for obstalces vis_x_inc ; increment to vis_x when testing for obstacles vis_y_inc ; increment to vis_y when testing for obstacles vis_step] ; number of patches needing to be tested for obstacles TO RESET_BOARD ;----------------------------------------------------------------------------------- set screen-half-width floor (world-width / 2) set screen-half-height floor (world-height / 2) ask patches [ ifelse ((abs pxcor) = screen-half-width) or ((abs pycor) = screen-half-height) [set pcolor green] ; colors patches green on edge of screen [set pcolor black] ; colors all other patches black ] end TO RESET_BIRDS ;----------------------------------------------------------------------------------- set screen-half-width floor (world-width / 2) set screen-half-height floor (world-height / 2) set w 30 ; sets width of blind spot obstacles_opaque ; calls procedure to make obstacles opaque ; to birds clear-turtles ; kills turtles crt number ; creates turtles and assigns them random positions ask turtles [ setxy ((random world-width) - screen-half-width) ((random world-height) - screen-half-height) ; and headings set heading random 360 set color scale-color red (abs (heading - 180)) 0 180 ; colors turtles according to their headings repeat 1000 [if pcolor = green ; randomly moves turtles that are in obstacles [setxy ((random world-width) - screen-half-width) ((random world-height) - screen-half-height)]] ] end TO OBSTACLES_TRANSPARENT ;------------------------------------------------------------------------- set obstacles_opaque? false ; sets "obstacles_opaque?" false end TO OBSTACLES_OPAQUE ;------------------------------------------------------------------------------ set obstacles_opaque? true ; sets "obstacles_opaque?" true end ;;;; TURTLE PROCEDURES ;;;; TO GO ;-------------------------------------------------------------------------------------------- set i 0 ; initializes variables used in finding neighbors set distance_1 1000 set distance_2 1000 set distance_3 1000 ; (below) determines ID numbers and distances for three closest neighbors; each turtle is ; first checked to be visible (i.e., out of blind spot and in front of obstacles), and then ; its distance is compared with that of neighbor_3. If a bird is closer than neighbor_3, ; it is then compared with neighbor_2 and (if it's closer than neighbor_2) with neighbor_1; ; variables are then re-assigned to accomodate the new neighbor as one of the closest three. repeat count turtles [ifelse not ((i = who) or in_blind_spot? or behind_opaque_obstacle?) [set dist distance turtle i ifelse dist < distance_3 [ifelse dist < distance_2 [set neighbor_3 neighbor_2 set distance_3 distance_2 ifelse dist < distance_1 [set neighbor_2 neighbor_1 set distance_2 distance_1 set neighbor_1 i set distance_1 dist] [set neighbor_2 i set distance_2 dist repeat 2 [fd 0]]] ; (see note at end for explanantion of "fd 0") [set neighbor_3 i set distance_3 dist repeat 4 [fd 0]]] [repeat 6 [fd 0]]] [repeat 7 [fd 0]] set i i + 1] set acceleration 0 ; sets acceleration to zero set target_1 calc_target neighbor_1 distance_1 ; calculates targets (see procedure below) based on set target_2 calc_target neighbor_2 distance_2 ; the headings and positions of each neighbor; set target_3 calc_target neighbor_3 distance_3 ; acceleration is set by the calc_target procedure ; (below) calculates a bird's composite target, weighting each individual target by the inverse ; of distance to that neighbor set target atan ((sin target_1) * 100 / distance_1 + (sin target_2) * 100 / distance_2 + (sin target_3) * 100 / distance_3) ((cos target_1) * 100 / distance_1 + (cos target_2) * 100 / distance_2 + (cos target_3) * 100 / distance_3) ; (below) turns bird towards target by a fraction specified by "flexibility"; random motion is also ; included to an extent governed by "noise". The "... + 540) mod 360) - 180" clause is necessary to ; ensure that the bird turns in the right direction. For example, if a bird is oriented at 0 degrees ; and its target is 300 degrees, it should consider a 60 [ = ((0 - 300 + 540) mod 360) - 180] degree ; turn to the left instead of a 300 [ = 300 - 0] degree turn to the right. lt (flexibility / 100 * (((heading - target + 540) mod 360) - 180)) + (random noise) - (random noise) set color scale-color red (abs (heading - 180)) -60 180 ; colors turtles according to new heading ifelse (([pcolor] of patch-at dx dy) = green) ; "bounces" birds off of obstacles as light would [ifelse (([pcolor] of patch-at 0 dy) = green) ; reflect off of a mirror [set heading 180 - heading ifelse (([pcolor] of patch-at dx 0) = green) [set heading 360 - heading] [fd 0]] ; (see note at end for explanantion of "fd 0") [fd 0 ifelse (([pcolor] of patch-at dx 0) = green) [set heading 360 - heading] [ifelse (abs cos heading) > (abs sin heading) [set heading 360 - heading] [set heading 180 - heading]]]] [repeat 2 [fd 0]] fd 1 + acceleration ; moves birds forward end TO-REPORT CALC_TARGET [the_neighbor the_distance] ;--------------------------------------------------------------- ; (below) calculates target by rules described in information window; please see note at end ; for an explanation of "fd 0" ifelse the_distance < repel_range [fd 0 report 180 + towards turtle the_neighbor] [ifelse the_distance < dir_range [fd 0 report [heading] of turtle the_neighbor] [ifelse the_distance < pos_range [ifelse (abs ((((heading - towards turtle the_neighbor) + 540) mod 360) - 180)) < 90 [set acceleration acceleration + 0.3] [set acceleration acceleration - 0.3] report towards turtle the_neighbor] [fd 0 report heading]]] end TO MAKE_OBSTACLE if mouse-down? [ask patches [ if ((abs (pxcor - mouse-xcor)) < 2) and ((abs (pycor - mouse-ycor)) < 2) [set pcolor green]] ] end TO REMOVE_OBSTACLE if mouse-down? [ask patches [ if ((abs (pxcor - mouse-xcor)) < 2) and ((abs (pycor - mouse-ycor)) < 2) [set pcolor black] ] ] end TO-REPORT BEHIND_OPAQUE_OBSTACLE? ;----------------------------------------------------------------------- if not obstacles_opaque? [report false] ; procedure ends and returns "false" if obstacles ; are not currently opaque set vis_x ([xcor] of turtle i) - xcor ; sets variables described above set vis_y ([ycor] of turtle i) - ycor set vis_step max list abs vis_x abs vis_y set vis_x_inc vis_x / vis_step set vis_y_inc vis_y / vis_step repeat vis_step ; checks the patches between a neighbor and the [if ([pcolor] of patch-at vis_x vis_y) = black ; bird in question, stopping on a patch that is [set vis_x vis_x - vis_x_inc ; an obstacle set vis_y vis_y - vis_y_inc]] ; (below) returns "false" if all patches between ; birds were checked, but returns "true" if the ; checker got stuck on an obstacle between birds report not (((round vis_x) = 0) and ((round vis_y) = 0)) end TO-REPORT IN_BLIND_SPOT? ;-------------------------------------------------------------------------------- ; (below) compares bird's heading with direction to a neighbor to see if it falls within the ; blind spot if 0 = distance turtle i [report false] report (abs ((((heading - towards-nowrap turtle i) + 360) mod 360) - 180)) < (w / 2) end @#$#@#$#@ GRAPHICS-WINDOW 303 10 801 529 30 30 8.0 1 10 1 1 1 0 1 1 1 -30 30 -30 30 0 0 1 ticks BUTTON 28 20 131 53 reset board reset_board NIL 1 T OBSERVER NIL NIL NIL NIL SLIDER 45 112 217 145 number number 0 50 40 1 1 birds HORIZONTAL SLIDER 45 151 217 184 repel_range repel_range 0 10 3 1 1 NIL HORIZONTAL SLIDER 45 190 217 223 dir_range dir_range 0 100 7 1 1 NIL HORIZONTAL SLIDER 45 228 217 261 pos_range pos_range 0 50 25 1 1 NIL HORIZONTAL SLIDER 45 267 217 300 flexibility flexibility 0 100 40 1 1 NIL HORIZONTAL SLIDER 45 305 217 338 noise noise 0 20 5 1 1 NIL HORIZONTAL BUTTON 138 20 236 53 reset birds reset_birds NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 28 58 131 91 cycle ask turtles [go] T 1 T OBSERVER NIL NIL NIL NIL BUTTON 138 59 236 92 go once ask turtles [go] NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 22 413 243 446 make obstacles opaque (default) obstacles_opaque NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 22 452 242 485 make obstacles transparent obstacles_transparent NIL 1 T OBSERVER NIL NIL NIL NIL BUTTON 22 376 130 409 make obstacle make_obstacle T 1 T OBSERVER NIL NIL NIL NIL BUTTON 133 376 242 409 remove obstacle remove_obstacle T 1 T OBSERVER NIL NIL NIL NIL @#$#@#$#@ WHAT IS IT? ------------ This project is an attempt to simulate the coordinated motion of a group of individuals such as fish in a school, or birds in a flock. Each bird follows a simple rule, and the flock as a whole moves without any leader. A bird adjusts its flight based on the position and/or heading of its three nearest neighbors; this adjustment is partitioned into three zones: 1) Repel range. A bird moves away from neighbors that are too close. 2) Direction range. A bird aligns with neighbors that are a comfortable distance away (i.e., it attempts to match the neighbor's heading.) 3) Position range. A bird moves towards neighbors that are far away. A bird adjusts its heading towards a vector sum of the "target" headings that these would imply for each neighbor; the influences of birds are weighted by the inverse of distance, such that close birds are more influential than distant ones. In addition, a bird will accelerate slightly for each neighbor in front of it and in the position range; it will decelerate slightly for each neighbor that is behind it and in the position range. This allows trailing birds to catch up with the flock and leading birds to slow down without turning around. All birds also have a blind spot (the default is 30 degrees) directly behind them, in which they cannot sense the presence of other birds. For the sake of simplicity, birds reflect off of obstacles as light would reflect off of a mirror. Though this is not necessarily realistic, it adds variety to the simulation by forcing the birds to continually adapt the flocking structure to outside influences. HOW TO USE IT ------------- The RESET_BOARD button erases all obstacles that have been drawn and restores the edge boundary. The RESET_TURTLES button creates the specified number of birds and places them in black cells on the board. The GO button executes the flocking rules described above; one button executes a step at a time and the other runs continuously. The MAKE_OBSTACLES and REMOVE_OBSTACLES buttons allow you to make obstacles that the birds must avoid, and to remove them. The OBSTACLES_TRANSPARENT and OBSTACLES_OPAQUE buttons toggle the way birds perceive obstacles in the middle of the screen. After selecting obstacles_transparent, birds can still see neighbors that are on the opposite side of an obstruction. Selecting obstacles_opaque (which is done by default in the reset_birds procedure) causes obstacles to block the birds' line of sight and hide neighbors that are behind obstacles. The step by step go button should be used when obstacles are opaque, because no attempt is made to synchronize the turtles' execution of commands when they are looking for obstacles. The NUMBER slider sets the number of birds in the simulation. The REPEL_RANGE, DIR_RANGE, and POS_RANGE sliders control the outer limits of each of these zones. The relative sizes must be maintained for the program to function properly (i.e. repel_range < dir_range < pos_range.) The NOISE slider determines the maximum random adjustment that a bird could make to its heading in a single time step. The FLEXIBILITY slider controls how completely a bird adjusts its heading to the calculated target. A flexibility of zero would cause a bird to maintain straight-line motion (excluding walls and random turns), while a flexibility of 100 represents instantaneous adjustment to the influences of the three closest neighbors. THINGS TO NOTICE ---------------- Obstacles can easily be created in the center of the screen by using the MAKE_OBSTACLE button; the flock remains quite cohesive when confronted with various shapes and sizes of obstacles. Cohesiveness is affected by the parameters, in particular flexibility and noise. CREDITS ------- Modified for NetLogo by B.J. MacLennan, October 2007, from original version by William Thies on Scott Camazine's website. Based on the Huth and Wissel (1992) model of fish schooling. @#$#@#$#@ default true 0 Polygon -7500403 true true 150 5 40 250 150 205 260 250 airplane true 0 Polygon -7500403 true true 150 0 135 15 120 60 120 105 15 165 15 195 120 180 135 240 105 270 120 285 150 270 180 285 210 270 165 240 180 180 285 195 285 165 180 105 180 60 165 15 arrow true 0 Polygon -7500403 true true 150 0 0 150 105 150 105 293 195 293 195 150 300 150 box false 0 Polygon -7500403 true true 150 285 285 225 285 75 150 135 Polygon -7500403 true true 150 135 15 75 150 15 285 75 Polygon -7500403 true true 15 75 15 225 150 285 150 135 Line -16777216 false 150 285 150 135 Line -16777216 false 150 135 15 75 Line -16777216 false 150 135 285 75 bug true 0 Circle -7500403 true true 96 182 108 Circle -7500403 true true 110 127 80 Circle -7500403 true true 110 75 80 Line -7500403 true 150 100 80 30 Line -7500403 true 150 100 220 30 butterfly true 0 Polygon -7500403 true true 150 165 209 199 225 225 225 255 195 270 165 255 150 240 Polygon -7500403 true true 150 165 89 198 75 225 75 255 105 270 135 255 150 240 Polygon -7500403 true true 139 148 100 105 55 90 25 90 10 105 10 135 25 180 40 195 85 194 139 163 Polygon -7500403 true true 162 150 200 105 245 90 275 90 290 105 290 135 275 180 260 195 215 195 162 165 Polygon -16777216 true false 150 255 135 225 120 150 135 120 150 105 165 120 180 150 165 225 Circle -16777216 true false 135 90 30 Line -16777216 false 150 105 195 60 Line -16777216 false 150 105 105 60 car false 0 Polygon -7500403 true true 300 180 279 164 261 144 240 135 226 132 213 106 203 84 185 63 159 50 135 50 75 60 0 150 0 165 0 225 300 225 300 180 Circle -16777216 true false 180 180 90 Circle -16777216 true false 30 180 90 Polygon -16777216 true false 162 80 132 78 134 135 209 135 194 105 189 96 180 89 Circle -7500403 true true 47 195 58 Circle -7500403 true true 195 195 58 circle false 0 Circle -7500403 true true 0 0 300 circle 2 false 0 Circle -7500403 true true 0 0 300 Circle -16777216 true false 30 30 240 cow false 0 Polygon -7500403 true true 200 193 197 249 179 249 177 196 166 187 140 189 93 191 78 179 72 211 49 209 48 181 37 149 25 120 25 89 45 72 103 84 179 75 198 76 252 64 272 81 293 103 285 121 255 121 242 118 224 167 Polygon -7500403 true true 73 210 86 251 62 249 48 208 Polygon -7500403 true true 25 114 16 195 9 204 23 213 25 200 39 123 cylinder false 0 Circle -7500403 true true 0 0 300 dot false 0 Circle -7500403 true true 90 90 120 face happy false 0 Circle -7500403 true true 8 8 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Polygon -16777216 true false 150 255 90 239 62 213 47 191 67 179 90 203 109 218 150 225 192 218 210 203 227 181 251 194 236 217 212 240 face neutral false 0 Circle -7500403 true true 8 7 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Rectangle -16777216 true false 60 195 240 225 face sad false 0 Circle -7500403 true true 8 8 285 Circle -16777216 true false 60 75 60 Circle -16777216 true false 180 75 60 Polygon -16777216 true false 150 168 90 184 62 210 47 232 67 244 90 220 109 205 150 198 192 205 210 220 227 242 251 229 236 206 212 183 fish false 0 Polygon -1 true false 44 131 21 87 15 86 0 120 15 150 0 180 13 214 20 212 45 166 Polygon -1 true false 135 195 119 235 95 218 76 210 46 204 60 165 Polygon -1 true false 75 45 83 77 71 103 86 114 166 78 135 60 Polygon -7500403 true true 30 136 151 77 226 81 280 119 292 146 292 160 287 170 270 195 195 210 151 212 30 166 Circle -16777216 true false 215 106 30 flag false 0 Rectangle -7500403 true true 60 15 75 300 Polygon -7500403 true true 90 150 270 90 90 30 Line -7500403 true 75 135 90 135 Line -7500403 true 75 45 90 45 flower false 0 Polygon -10899396 true false 135 120 165 165 180 210 180 240 150 300 165 300 195 240 195 195 165 135 Circle -7500403 true true 85 132 38 Circle -7500403 true true 130 147 38 Circle -7500403 true true 192 85 38 Circle -7500403 true true 85 40 38 Circle -7500403 true true 177 40 38 Circle -7500403 true true 177 132 38 Circle -7500403 true true 70 85 38 Circle -7500403 true true 130 25 38 Circle -7500403 true true 96 51 108 Circle -16777216 true false 113 68 74 Polygon -10899396 true false 189 233 219 188 249 173 279 188 234 218 Polygon -10899396 true false 180 255 150 210 105 210 75 240 135 240 house false 0 Rectangle -7500403 true true 45 120 255 285 Rectangle -16777216 true false 120 210 180 285 Polygon -7500403 true true 15 120 150 15 285 120 Line -16777216 false 30 120 270 120 leaf false 0 Polygon -7500403 true true 150 210 135 195 120 210 60 210 30 195 60 180 60 165 15 135 30 120 15 105 40 104 45 90 60 90 90 105 105 120 120 120 105 60 120 60 135 30 150 15 165 30 180 60 195 60 180 120 195 120 210 105 240 90 255 90 263 104 285 105 270 120 285 135 240 165 240 180 270 195 240 210 180 210 165 195 Polygon -7500403 true true 135 195 135 240 120 255 105 255 105 285 135 285 165 240 165 195 line true 0 Line -7500403 true 150 0 150 300 line half true 0 Line -7500403 true 150 0 150 150 link true 0 Line -7500403 true 150 0 150 300 link direction true 0 Line -7500403 true 150 150 30 225 Line -7500403 true 150 150 270 225 pentagon false 0 Polygon -7500403 true true 150 15 15 120 60 285 240 285 285 120 person false 0 Circle -7500403 true true 110 5 80 Polygon -7500403 true true 105 90 120 195 90 285 105 300 135 300 150 225 165 300 195 300 210 285 180 195 195 90 Rectangle -7500403 true true 127 79 172 94 Polygon -7500403 true true 195 90 240 150 225 180 165 105 Polygon -7500403 true true 105 90 60 150 75 180 135 105 plant false 0 Rectangle -7500403 true true 135 90 165 300 Polygon -7500403 true true 135 255 90 210 45 195 75 255 135 285 Polygon -7500403 true true 165 255 210 210 255 195 225 255 165 285 Polygon -7500403 true true 135 180 90 135 45 120 75 180 135 210 Polygon -7500403 true true 165 180 165 210 225 180 255 120 210 135 Polygon -7500403 true true 135 105 90 60 45 45 75 105 135 135 Polygon -7500403 true true 165 105 165 135 225 105 255 45 210 60 Polygon -7500403 true true 135 90 120 45 150 15 180 45 165 90 square false 0 Rectangle -7500403 true true 30 30 270 270 square 2 false 0 Rectangle -7500403 true true 30 30 270 270 Rectangle -16777216 true false 60 60 240 240 star false 0 Polygon -7500403 true true 151 1 185 108 298 108 207 175 242 282 151 216 59 282 94 175 3 108 116 108 target false 0 Circle -7500403 true true 0 0 300 Circle -16777216 true false 30 30 240 Circle -7500403 true true 60 60 180 Circle -16777216 true false 90 90 120 Circle -7500403 true true 120 120 60 tree false 0 Circle -7500403 true true 118 3 94 Rectangle -6459832 true false 120 195 180 300 Circle -7500403 true true 65 21 108 Circle -7500403 true true 116 41 127 Circle -7500403 true true 45 90 120 Circle -7500403 true true 104 74 152 triangle false 0 Polygon -7500403 true true 150 30 15 255 285 255 triangle 2 false 0 Polygon -7500403 true true 150 30 15 255 285 255 Polygon -16777216 true false 151 99 225 223 75 224 truck false 0 Rectangle -7500403 true true 4 45 195 187 Polygon -7500403 true true 296 193 296 150 259 134 244 104 208 104 207 194 Rectangle -1 true false 195 60 195 105 Polygon -16777216 true false 238 112 252 141 219 141 218 112 Circle -16777216 true false 234 174 42 Rectangle -7500403 true true 181 185 214 194 Circle -16777216 true false 144 174 42 Circle -16777216 true false 24 174 42 Circle -7500403 false true 24 174 42 Circle -7500403 false true 144 174 42 Circle -7500403 false true 234 174 42 turtle true 0 Polygon -10899396 true false 215 204 240 233 246 254 228 266 215 252 193 210 Polygon -10899396 true false 195 90 225 75 245 75 260 89 269 108 261 124 240 105 225 105 210 105 Polygon -10899396 true false 105 90 75 75 55 75 40 89 31 108 39 124 60 105 75 105 90 105 Polygon -10899396 true false 132 85 134 64 107 51 108 17 150 2 192 18 192 52 169 65 172 87 Polygon -10899396 true false 85 204 60 233 54 254 72 266 85 252 107 210 Polygon -7500403 true true 119 75 179 75 209 101 224 135 220 225 175 261 128 261 81 224 74 135 88 99 wheel false 0 Circle -7500403 true true 3 3 294 Circle -16777216 true false 30 30 240 Line -7500403 true 150 285 150 15 Line -7500403 true 15 150 285 150 Circle -7500403 true true 120 120 60 Line -7500403 true 216 40 79 269 Line -7500403 true 40 84 269 221 Line -7500403 true 40 216 269 79 Line -7500403 true 84 40 221 269 x false 0 Polygon -7500403 true true 270 75 225 30 30 225 75 270 Polygon -7500403 true true 30 75 75 30 270 225 225 270 @#$#@#$#@ NetLogo 4.1 @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ @#$#@#$#@ default 0.0 -0.2 0 0.0 1.0 0.0 1 1.0 0.0 0.2 0 0.0 1.0 link direction true 0 Line -7500403 true 150 150 90 180 Line -7500403 true 150 150 210 180 @#$#@#$#@ 0 @#$#@#$#@