This 12th step illustrates how to load an image file and to use it to initialize a grid.
We add a new global variable: the image file:
file map_init <- image_file("../images/predator_prey_raster_map.png");
The image file is here: 
You have to copy it in your project folder: images/
In order to have a more complex environment, we want to use this image as the initialization of the environment. The food level available in a vegetation_cell will be based on the green level of the corresponding pixel in the image. You will be able to use such process to represent existing real environment in your model. We modify the global init of the model in order to cast the image file in a matrix. We use for that the file as_matrix {nb_cols, nb_lines} operator that allows to convert a file (image, csv) to a matrix composed of nb_cols columns and nb_lines lines.
Concerning the manipulation of matrix, it is possible to obtain the element [i,j] of a matrix by using my_matrix [i,j].
A grid can be view as spatial matrix: each cell of a grid has two built-in variables grid_x and grid_y that represent the column and line indexes of the cell.
init {
create prey number: nb_preys_init ;
create predator number: nb_predators_init ;
matrix init_data <- map_init as_matrix {50,50};
ask vegetation_cell {
color <- rgb (init_data[grid_x,grid_y]) ;
food <- 1 - ((color as list)[0] / 255) ;
foodProd <- food / 100 ;
}
}
Congratulations, you have complete your first GAMA models! Now, you know have enough knowledge to create many models that includes: dynamic grid-based environment, moving and interacting agents and the needed viusalization to make good use of your simulation. Feel free to use this knowledge to create your very own models! Or perhaps you want to continue your study with the more advanced tutorials?
model prey_predator
global {
int nb_preys_init <- 200;
int nb_predators_init <- 20;
float prey_max_energy <- 1.0;
float prey_max_transfert <- 0.1 ;
float prey_energy_consum <- 0.05;
float predator_max_energy <- 1.0;
float predator_energy_transfert <- 0.5;
float predator_energy_consum <- 0.02;
float prey_proba_reproduce <- 0.01;
int prey_nb_max_offsprings <- 5;
float prey_energy_reproduce <- 0.5;
float predator_proba_reproduce <- 0.01;
int predator_nb_max_offsprings <- 3;
float predator_energy_reproduce <- 0.5;
file map_init <- image_file("../images/predator_prey_raster_map.png");
int nb_preys -> {length (prey)};
int nb_predators -> {length (predator)};
init {
create prey number: nb_preys_init ;
create predator number: nb_predators_init ;
ask vegetation_cell {
color <- rgb (map_init at {grid_x,grid_y}) ;
food <- 1 - (((color as list)[0]) / 255) ;
foodProd <- food / 100 ;
}
}
reflex save_result when: (nb_preys > 0) and (nb_predators > 0){
save ("cycle: "+ cycle + "; nbPreys: " + nb_preys
+ "; minEnergyPreys: " + ((prey as list) min_of each.energy)
+ "; maxSizePreys: " + ((prey as list) max_of each.energy)
+ "; nbPredators: " + nb_predators
+ "; minEnergyPredators: " + ((predator as list) min_of each.energy)
+ "; maxSizePredators: " + ((predator as list) max_of each.energy))
to: "results.txt" type: "text" ;
}
reflex stop_simulation when: (nb_preys = 0) or (nb_predators = 0) {
do halt ;
}
}
species generic_species {
float size <- 1.0;
rgb color ;
float max_energy;
float max_transfert;
float energy_consum;
float proba_reproduce ;
float nb_max_offsprings;
float energy_reproduce;
file my_icon;
vegetation_cell myCell <- one_of (vegetation_cell) ;
float energy <- (rnd(1000) / 1000) * max_energy update: energy - energy_consum max: max_energy ;
init {
location <- myCell.location;
}
reflex basic_move {
myCell <- choose_cell();
location <- myCell.location;
}
vegetation_cell choose_cell {
return nil;
}
reflex die when: energy <= 0 {
do die ;
}
reflex reproduce when: (energy >= energy_reproduce) and (flip(proba_reproduce)) {
int nb_offsprings <- 1 + rnd(nb_max_offsprings -1);
create species(self) number: nb_offsprings {
myCell <- myself.myCell ;
location <- myCell.location ;
energy <- myself.energy / nb_offsprings ;
}
energy <- energy / nb_offsprings ;
}
aspect base {
draw circle(size) color: color ;
}
aspect icon {
draw my_icon size: 2 * size ;
}
aspect info {
draw square(size) color: color ;
draw string(energy with_precision 2) size: 3 color: #black ;
}
}
species prey parent: generic_species {
rgb color <- #blue;
float max_energy <- prey_max_energy ;
float max_transfert <- prey_max_transfert ;
float energy_consum <- prey_energy_consum ;
float proba_reproduce <- prey_proba_reproduce ;
int nb_max_offsprings <- prey_nb_max_offsprings ;
float energy_reproduce <- prey_energy_reproduce ;
file my_icon <- file("../images/predator_prey_sheep.png") ;
reflex eat when: myCell.food > 0 {
float energy_transfert <- min([max_transfert, myCell.food]) ;
myCell.food <- myCell.food - energy_transfert ;
energy <- energy + energy_transfert ;
}
vegetation_cell choose_cell {
return (myCell.neighbours) with_max_of (each.food);
}
}
species predator parent: generic_species {
rgb color <- #red ;
float max_energy <- predator_max_energy ;
float energy_transfert <- predator_energy_transfert ;
float energy_consum <- predator_energy_consum ;
list<prey> reachable_preys update: prey inside (myCell);
float proba_reproduce <- predator_proba_reproduce ;
int nb_max_offsprings <- predator_nb_max_offsprings ;
float energy_reproduce <- predator_energy_reproduce ;
file my_icon <- file("../images/predator_prey_wolf.png") ;
reflex eat when: ! empty(reachable_preys) {
ask one_of (reachable_preys) {
do die ;
}
energy <- energy + energy_transfert ;
}
vegetation_cell choose_cell {
vegetation_cell myCell_tmp <- shuffle(myCell.neighbours) first_with (!(empty (prey inside (each))));
if myCell_tmp != nil {
return myCell_tmp;
} else {
return one_of (myCell.neighbours);
}
}
}
grid vegetation_cell width: 50 height: 50 neighbours: 4 {
float maxFood <- 1.0 ;
float foodProd <- (rnd(1000) / 1000) * 0.01 ;
float food <- (rnd(1000) / 1000) max: maxFood update: food + foodProd ;
rgb color <- rgb(int(255 * (1 - food)), 255, int(255 * (1 - food))) update: rgb(int(255 * (1 - food)), 255, int(255 *(1 - food))) ;
list<vegetation_cell> neighbours <- (self neighbours_at 2);
}
experiment prey_predator type: gui {
parameter "Initial number of preys: " var: nb_preys_init min: 0 max: 1000 category: "Prey" ;
parameter "Prey max energy: " var: prey_max_energy category: "Prey" ;
parameter "Prey max transfert: " var: prey_max_transfert category: "Prey" ;
parameter "Prey energy consumption: " var: prey_energy_consum category: "Prey" ;
parameter "Initial number of predators: " var: nb_predators_init min: 0 max: 200 category: "Predator" ;
parameter "Predator max energy: " var: predator_max_energy category: "Predator" ;
parameter "Predator energy transfert: " var: predator_energy_transfert category: "Predator" ;
parameter "Predator energy consumption: " var: predator_energy_consum category: "Predator" ;
parameter 'Prey probability reproduce: ' var: prey_proba_reproduce category: 'Prey' ;
parameter 'Prey nb max offsprings: ' var: prey_nb_max_offsprings category: 'Prey' ;
parameter 'Prey energy reproduce: ' var: prey_energy_reproduce category: 'Prey' ;
parameter 'Predator probability reproduce: ' var: predator_proba_reproduce category: 'Predator' ;
parameter 'Predator nb max offsprings: ' var: predator_nb_max_offsprings category: 'Predator' ;
parameter 'Predator energy reproduce: ' var: predator_energy_reproduce category: 'Predator' ;
output {
display main_display {
grid vegetation_cell lines: #black ;
species prey aspect: icon ;
species predator aspect: icon ;
}
display info_display {
grid vegetation_cell lines: #black ;
species prey aspect: info ;
species predator aspect: info ;
}
display Population_information refresh:every(5) {
chart "Species evolution" type: series size: {1,0.5} position: {0, 0} {
data "number_of_preys" value: nb_preys color: #blue ;
data "number_of_predator" value: nb_predators color: #red ;
}
chart "Prey Energy Distribution" type: histogram background: rgb("lightGray") size: {0.5,0.5} position: {0, 0.5} {
data "]0;0.25]" value: prey count (each.energy <= 0.25) color:#blue;
data "]0.25;0.5]" value: prey count ((each.energy > 0.25) and (each.energy <= 0.5)) color:#blue;
data "]0.5;0.75]" value: prey count ((each.energy > 0.5) and (each.energy <= 0.75)) color:#blue;
data "]0.75;1]" value: prey count (each.energy > 0.75) color:#blue;
}
chart "Predator Energy Distribution" type: histogram background: rgb("lightGray") size: {0.5,0.5} position: {0.5, 0.5} {
data "]0;0.25]" value: predator count (each.energy <= 0.25) color: #red ;
data "]0.25;0.5]" value: predator count ((each.energy > 0.25) and (each.energy <= 0.5)) color: #red ;
data "]0.5;0.75]" value: predator count ((each.energy > 0.5) and (each.energy <= 0.75)) color: #red ;
data "]0.75;1]" value: predator count (each.energy > 0.75) color: #red;
}
}
monitor "Number of preys" value: nb_preys;
monitor "Number of predators" value: nb_predators;
}
}