Autonomous robots can move through a room without being told every step because they build a map as they travel. A robot vacuum is a familiar example: it scans walls, furniture, and open floor space while estimating where it is. This process matters because robots need both a map and a position on that map to plan safe paths.
Without mapping, a robot would waste time, miss areas, or bump into obstacles.
Key Facts
- SLAM stands for Simultaneous Localization and Mapping.
- Localization means estimating the robot's position and direction in the room.
- Mapping means building a model of walls, obstacles, and open space.
- LIDAR estimates distance using d = vt/2, where v is light speed and t is round trip time.
- An occupancy grid divides the room into cells marked free, occupied, or unknown.
- Wheel odometry estimates travel using distance = wheel circumference × number of rotations.
Vocabulary
- SLAM
- SLAM is the process a robot uses to build a map of an unknown area while also tracking its own location.
- LIDAR
- LIDAR is a sensing method that uses laser light to measure distances to nearby objects and surfaces.
- Occupancy grid
- An occupancy grid is a map made of small cells that show whether each part of the space is open, blocked, or still unknown.
- Localization
- Localization is the robot's estimate of where it is and which direction it is facing.
- Odometry
- Odometry is the use of wheel motion or motor data to estimate how far and in what direction a robot has moved.
Common Mistakes to Avoid
- Treating the map as perfect is wrong because sensor readings can be noisy, blocked, or reflected by shiny surfaces.
- Forgetting that the robot must track its own position is wrong because a map is only useful if the robot knows where it is on that map.
- Assuming wheel rotations give exact distance is wrong because wheels can slip on rugs, cords, or smooth floors.
- Marking every unseen space as blocked is wrong because unknown cells are different from obstacles until the robot scans them.
Practice Questions
- 1 A robot's wheel circumference is 20 cm. If the wheel turns 15 times, how far does the robot estimate it has traveled in centimeters and meters?
- 2 A LIDAR pulse has a round trip time of 20 ns. Using v = 3.0 × 10^8 m/s, calculate the distance to the wall with d = vt/2.
- 3 A robot vacuum enters a room with a couch, table legs, and an open doorway. Explain why it needs both LIDAR measurements and odometry to make a reliable map.