Your Family Will Thank You For Getting This Lidar Robot Navigation
LiDAR Robot Navigation
LiDAR robots navigate using a combination of localization and mapping, and also path planning. This article will explain the concepts and demonstrate how they function using an example in which the robot achieves a goal within a row of plants.
LiDAR sensors have low power requirements, allowing them to extend a robot's battery life and decrease the amount of raw data required for localization algorithms.
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LiDAR Sensors
The sensor is the heart of Lidar systems. It releases laser pulses into the surrounding. The light waves hit objects around and bounce back to the sensor at various angles, based on the composition of the object. The sensor determines how long it takes each pulse to return and utilizes that information to determine distances. The sensor is typically placed on a rotating platform allowing it to quickly scan the entire area at high speed (up to 10000 samples per second).
LiDAR sensors are classified by whether they are designed for applications in the air or on land. Airborne lidar systems are typically connected to aircrafts, helicopters or unmanned aerial vehicles (UAVs). Terrestrial LiDAR systems are usually mounted on a static robot platform.
To accurately measure distances, the sensor must be aware of the precise location of the robot at all times. This information is usually captured through a combination of inertial measurement units (IMUs), GPS, and time-keeping electronics. These sensors are used by LiDAR systems in order to determine the precise location of the sensor in space and time. This information is then used to create a 3D model of the environment.
LiDAR scanners can also identify various types of surfaces which is especially useful when mapping environments that have dense vegetation. For instance, if an incoming pulse is reflected through a canopy of trees, it is likely to register multiple returns. Typically, the first return is attributed to the top of the trees, while the final return is attributed to the ground surface. If the sensor records these pulses separately this is known as discrete-return LiDAR.
The Discrete Return scans can be used to analyze the structure of surfaces. For instance, a forested region could produce the sequence of 1st 2nd and 3rd return, with a final large pulse representing the ground. The ability to separate and store these returns as a point cloud allows for detailed terrain models.
Once an 3D map of the surrounding area has been created and the robot has begun to navigate using this data. This involves localization as well as building a path that will take it to a specific navigation "goal." It also involves dynamic obstacle detection. This is the process of identifying obstacles that are not present in the original map, and adjusting the path plan accordingly.
SLAM Algorithms

SLAM (simultaneous localization and mapping) is an algorithm that allows your robot to create an image of its surroundings and then determine the position of the robot relative to the map. Engineers utilize this information for a variety of tasks, including planning routes and obstacle detection.
To enable SLAM to function, your robot must have a sensor (e.g. A computer that has the right software for processing the data as well as either a camera or laser are required. You will also need an IMU to provide basic positioning information. The result is a system that can accurately determine the location of your robot in an unknown environment.
The SLAM process is complex, and many different back-end solutions exist. Whatever solution you choose, a successful SLAM system requires a constant interplay between the range measurement device and the software that extracts the data, and the vehicle or robot. It is a dynamic process that is almost indestructible.
As the robot moves the area, it adds new scans to its map. The SLAM algorithm compares these scans to prior ones making use of a process known as scan matching. This aids in establishing loop closures. The SLAM algorithm is updated with its robot's estimated trajectory when a loop closure has been identified.
Another factor that makes SLAM is the fact that the surrounding changes over time. For instance, if your robot travels down an empty aisle at one point, and then comes across pallets at the next spot, it will have difficulty finding these two points on its map. This is where the handling of dynamics becomes important, and this is a typical characteristic of the modern Lidar SLAM algorithms.
SLAM systems are extremely efficient in 3D scanning and navigation despite the challenges. It is especially beneficial in situations that don't rely on GNSS for its positioning for example, an indoor factory floor. It is important to remember that even a well-configured SLAM system can experience errors. It is essential to be able to detect these flaws and understand how they impact the SLAM process in order to fix them.
Mapping
The mapping function creates a map for a robot's environment. This includes the robot, its wheels, actuators and everything else that is within its vision field. The map is used to perform localization, path planning and obstacle detection. This is an area in which 3D lidars are extremely helpful, as they can be utilized like an actual 3D camera (with a single scan plane).
Map building is a time-consuming process however, it is worth it in the end. The ability to create an accurate, complete map of the robot's surroundings allows it to conduct high-precision navigation as well being able to navigate around obstacles.
In general, the greater the resolution of the sensor then the more accurate will be the map. Not all robots require high-resolution maps. For example floor sweepers might not require the same level detail as an industrial robotic system that is navigating factories of a large size.
This is why there are a variety of different mapping algorithms that can be used with LiDAR sensors. One of the most popular algorithms is Cartographer which employs the two-phase pose graph optimization technique to correct for drift and maintain an accurate global map. It is particularly effective when used in conjunction with Odometry.
GraphSLAM is another option, which uses a set of linear equations to represent the constraints in the form of a diagram. The constraints are modelled as an O matrix and a X vector, with each vertice of the O matrix representing a distance to a landmark on the X vector. A GraphSLAM update is a series of additions and subtraction operations on these matrix elements, with the end result being that all of the X and O vectors are updated to accommodate new information about the robot.
SLAM+ is another useful mapping algorithm that combines odometry with mapping using an Extended Kalman filter (EKF). The EKF updates the uncertainty of the robot's position as well as the uncertainty of the features that were mapped by the sensor. This information can be used by the mapping function to improve its own estimation of its location, and also to update the map.
Obstacle Detection
A robot needs to be able to see its surroundings to avoid obstacles and get to its desired point. It uses sensors like digital cameras, infrared scanners laser radar and sonar to determine its surroundings. It also makes use of an inertial sensors to determine its speed, location and orientation. These sensors assist it in navigating in a safe manner and prevent collisions.
A range sensor is used to measure the distance between a robot and an obstacle. The sensor can be placed on the robot, in an automobile or on the pole. It is important to keep in mind that the sensor is affected by a myriad of factors like rain, wind and fog. Therefore, it is essential to calibrate the sensor prior every use.
A crucial step in obstacle detection is the identification of static obstacles, which can be accomplished using the results of the eight-neighbor-cell clustering algorithm. This method isn't particularly precise due to the occlusion caused by the distance between laser lines and the camera's angular velocity. To overcome this problem multi-frame fusion was implemented to increase the effectiveness of static obstacle detection.
The method of combining roadside camera-based obstruction detection with the vehicle camera has proven to increase the efficiency of data processing. It also provides redundancy for other navigation operations, like path planning. The result of this technique is a high-quality picture of the surrounding environment that is more reliable than one frame. In outdoor tests the method was compared against other methods for detecting obstacles like YOLOv5 monocular ranging, VIDAR.
The results of the test showed that the algorithm could accurately identify the height and location of an obstacle, as well as its tilt and rotation. It also had a good performance in identifying the size of obstacles and its color. The method also exhibited excellent stability and durability even in the presence of moving obstacles.