光達

光達（LIDAR）會測量機器人周圍一整圈的距離，單位是公尺，就像同時使用許多個距離感測器。在入門機器人上，它的名稱是 lidar，位於機器人頂部。

它會在機器人周圍測量 512 個點，分成上下堆疊的 4 層，最遠 1 m。沒有碰到任何物體的點會讀到 inf。

讀取距離

getLayerRangeImage(0) 會提供一層的 512 個距離。第一個點在機器人正前方，接著順時針排列：四分之一處在右方，一半處在後方，四分之三處在左方。

Python

from controller import Robot

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

lidar = robot.getDevice("lidar")
lidar.enable(timeStep)
n = lidar.getHorizontalResolution()  # Number of points in each layer
print("Points per layer:", n, "Layers:", lidar.getNumberOfLayers())

while robot.step(timeStep) != -1:
    distances = lidar.getLayerRangeImage(0)  # One layer, in meters, clockwise from the front
    front = distances[0]
    right = distances[n // 4]
    back = distances[n // 2]
    left = distances[3 * n // 4]
    print("front:", round(front, 3), "right:", round(right, 3), "back:", round(back, 3), "left:", round(left, 3))

C/C++

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

using namespace webots;
using namespace std;

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

  Lidar *lidar = robot->getLidar("lidar");
  lidar->enable(timeStep);
  int n = lidar->getHorizontalResolution(); // Number of points in each layer
  cout << "Points per layer: " << n << " Layers: " << lidar->getNumberOfLayers() << endl;

  while (robot->step(timeStep) != -1) {
    const float *distances = lidar->getLayerRangeImage(0); // One layer, in meters, clockwise from the front
    cout << "front: " << distances[0] << " right: " << distances[n / 4] << " back: " << distances[n / 2]
         << " left: " << distances[3 * n / 4] << endl;
  }

  delete robot;
  return 0;
}

下圖是入門機器人在 world1.wbt 中測得的一層資料，從上方繪製，機器人位於中央。周圍的牆壁會顯示成一排排的點。

點雲

光達也可以把每個點提供為相對於光達的位置，這對畫出機器人所見的地圖很有用。計算點雲需要額外的時間，所以只有在會用到時才啟用它。

Python

from controller import Robot

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

lidar = robot.getDevice("lidar")
lidar.enable(timeStep)
lidar.enablePointCloud()  # Computing the point cloud takes extra time

while robot.step(timeStep) != -1:
    points = lidar.getPointCloud()
    point = points[0]  # Positions relative to the lidar, in meters
    print("x:", round(point.x, 3), "y:", round(point.y, 3), "z:", round(point.z, 3), "layer:", point.layer)

C/C++

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

using namespace webots;
using namespace std;

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

  Lidar *lidar = robot->getLidar("lidar");
  lidar->enable(timeStep);
  lidar->enablePointCloud(); // Computing the point cloud takes extra time

  while (robot->step(timeStep) != -1) {
    const LidarPoint *points = lidar->getPointCloud();
    const LidarPoint &point = points[0]; // Positions relative to the lidar, in meters
    cout << "x: " << point.x << " y: " << point.y << " z: " << point.z << " layer: " << point.layer_id << endl;
  }

  delete robot;
  return 0;
}

放置光達

在你自己的機器人中，請把光達放在頂部，並使用與入門機器人相同的旋轉角度，讓它保持水平。如果放在機身內部或傾斜放置，它會測量到機器人本身。