Distance Sensor

A distance sensor measures the distance, in metres, to the first object in front of it, up to 0.8 m. The starter robot has three: leftDist, frontDist and rightDist, looking left, forward and right.

Reading a sensor

Python

from controller import Robot

robot = Robot()
timeStep = int(robot.getBasicTimeStep())

frontDist = robot.getDevice("frontDist")  # Get the sensor by name
frontDist.enable(timeStep)                 # Enable it

while robot.step(timeStep) != -1:
    print("Front:", round(frontDist.getValue(), 3), "m")

C/C++

#include <iostream>
#include <webots/Robot.hpp>
#include <webots/DistanceSensor.hpp>

using namespace webots;
using namespace std;

int main() {
  Robot *robot = new Robot();
  int timeStep = (int)robot->getBasicTimeStep();

  DistanceSensor *frontDist = robot->getDistanceSensor("frontDist"); // Get the sensor by name
  frontDist->enable(timeStep);                                        // Enable it

  while (robot->step(timeStep) != -1)
    cout << "Front: " << frontDist->getValue() << " m" << endl;

  delete robot;
  return 0;
}

Finding walls

A tile is 12 cm wide, so when the robot is in the middle of a tile, a wall on its side is about 5 cm away. This program checks the three sensors, and prints which ones see a wall:

Python

from controller import Robot

robot = Robot()
timeStep = int(robot.getBasicTimeStep())

# Keep the sensors in a dictionary, to use them by name
sensors = {}
for name in ["leftDist", "frontDist", "rightDist"]:
    sensors[name] = robot.getDevice(name)
    sensors[name].enable(timeStep)

WALL = 0.07  # Closer than 7 cm counts as a wall next to the robot

while robot.step(timeStep) != -1:
    walls = [name for name, sensor in sensors.items() if sensor.getValue() < WALL]
    print("Walls:", walls)

C/C++

#include <iostream>
#include <string>
#include <vector>
#include <webots/Robot.hpp>
#include <webots/DistanceSensor.hpp>

using namespace webots;
using namespace std;

int main() {
  Robot *robot = new Robot();
  int timeStep = (int)robot->getBasicTimeStep();

  vector<string> names = {"leftDist", "frontDist", "rightDist"};
  vector<DistanceSensor *> sensors;
  for (const string &name : names) {
    sensors.push_back(robot->getDistanceSensor(name));
    sensors.back()->enable(timeStep);
  }

  const double WALL = 0.07; // Closer than 7 cm counts as a wall next to the robot

  while (robot->step(timeStep) != -1) {
    cout << "Walls:";
    for (size_t i = 0; i < sensors.size(); i++)
      if (sensors[i]->getValue() < WALL)
        cout << " " << names[i];
    cout << endl;
  }

  delete robot;
  return 0;
}

Sensors measure from where they are on the robot, not from its centre. Print the values next to a wall to choose your own limits.