PredatorPrey_step12

12. Image loading

This 12th step illustrates how to load an image file and to use it to initialize a grid.

Formulation

• Building of the initial environment (food and food_prod of the cells) from an image file.

Model Definition

global variable

We add a new global variable to store the image data:

file map_init <- image_file("../includes/data/raster_map.png");

The image file is here:

You have to copy it in your project folder: includes/data/.

Model initialization

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 a process to represent an existing real environment in your model.

We modify the global init of the model in order to cast the image file in a matrix.

First of all, when the variable map_init is defined from an image file (or a csv file), it can be manipulated directly as a matrix, with the dimensions of the image (here it is a 50x50 image, which matches with the grid size). In the case we need to resize the image, we can use the file as_matrix {nb_cols, nb_lines} operator that allows converting a file (image, csv) to a matrix composed of nb_cols columns and nb_lines lines.

Concerning the manipulation of a 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 a 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 ;
    ask vegetation_cell {
	color <- rgb (map_init at {grid_x,grid_y}) ;
	food <- 1 - (((color as list) at 0) / 255) ;
	food_prod <- food / 100 ; 
    }
}

Complete Model

https://github.com/gama-platform/gama/blob/main/gama.library/tutorials/Predator%20Prey/models/Model%2012.gaml