Mountain Runners

Let's consider a race to the top of a mountain. Runners have been scattered about a map in some low lying areas and need to find the best path up to the peak.

We'll use Pathfinding.Pathfinder and a Pathfinding.HeightMap to simulate this.

Setup

using Agents, Agents.Pathfinding
using Random
using FileIO # To load images you also need ImageMagick available to your project

@agent Runner GridAgent{2} begin end

Our agent, as you can see, is very simple. Just an id and position provided by @agent. The rest of the dynamics of this example will be provided by the model.

function initialize(map_url; goal = (128, 409), seed = 88)
    # Load an image file and convert it do a simple representation of height
    heightmap = floor.(Int, convert.(Float64, load(download(map_url))) * 255)
    # The space of the model can be obtained directly from the image.
    # Our example file is (400, 500).

    # The pathfinder. We use the `MaxDistance` metric since we want the runners
    # to look for the easiest path to run, not just the most direct.
    pathfinder = Pathfinder(cost_metric = HeightMap(heightmap, MaxDistance{2}()))
    space = GridSpace(size(heightmap); pathfinder, periodic = false)
    model =
        ABM(Runner, space; rng = MersenneTwister(seed), properties = Dict(:goal => goal))
    for _ in 1:10
        # Place runners in the low-lying space in the map.
        runner = add_agent!((rand(model.rng, 100:350), rand(model.rng, 50:200)), model)
        # Everyone wants to get to the same place.
        set_target!(runner, goal, model)
    end
    return model
end

initialize (generic function with 1 method)

The example heightmap we use here is a small region of countryside in Sweden, obtained with the Tangram heightmapper.

Dynamics

With the pathfinder in place, and all our runners having a goal position set, stepping is now trivial.

agent_step!(agent, model) = move_along_route!(agent, model)

agent_step! (generic function with 1 method)

Let's Race

Plotting is simple enough. We just need to use the InteractiveDynamics.abm_plot for our runners, and display the heightmap for our reference. A better interface to do this is currently a work in progress.

using InteractiveDynamics
using CairoMakie

We load the sample heightmap

map_url =
    "https://raw.githubusercontent.com/JuliaDynamics/" *
    "JuliaDynamics/master/videos/agents/runners_heightmap.jpg"
model = initialize(map_url)

AgentBasedModel with 10 agents of type Runner
 space: GridSpace with size (400, 500), metric=chebyshev, periodic=false, pathfinder=A* in 2 dimensions, diagonal, ϵ=0.0, metric=HeightMap with base: MaxDistance
 scheduler: fastest
 properties: Dict(:goal => (128, 409))

and plot

static_preplot!(ax, model) = scatter!(ax, model.goal; color = (:red, 50), marker = 'x')

abm_video(
    "runners.mp4",
    model,
    agent_step!;
    resolution = (700, 700),
    frames = 410,
    framerate = 45,
    ac = :black,
    as = 8,
    scatterkwargs = (strokecolor = :white, strokewidth = 2),
    heatarray = model -> heightmap(model),
    heatkwargs = (colormap = :terrain,),
    static_preplot!
)