W08: AV Perception
Self-sensing
Uses sensors to measure current state of vehicle
Localisation
Uses sensors to determine vehicle's global and local position
Eg. Global Positioning System to determine geographic location
Surrounding-sensing
Uses sensors to sense surrounding
Eg. Hall effect sensor to measure vehicle velocity, Inertial Measurement Unit (IMU) to measure acceleration
Eg. Camera to provide road markings, LiDAR to detect obstacles
FAQ
Accuracy
The error between the true value and its measurement, which include noise levels and external interference rejection parameters
Resolution
The minimum difference between two measurements
Sensitivity
The smallest value that can be detected or measured
Dynamic Range
The minimum and maximum values that can be detected
Perspective
Quantities such as sensor range or its field of view
Active VS Passive
Whether the sensor emits energy or radiation that illuminates the environment or relies on ambient conditions
Timescale
Quantities such as update rate of sensor output and the frequency bandwidth of the measurement output over time
Output or interface technology
How the information is transmitted from the sensor to controller such as analogue voltage or current, digital outputs, serial or network data streams
Commonly available measurement on vehicles
Wheel speed
Produce a digital signal where its frequency is proportional to speed
Vehicle dynamic state
Include yaw rate, lateral and longitudinal acceleration
Driver inputs
Includes throttle and brake pedal positions, turn signals, headlights, steering wheel position
Brake pressure
Either at the master cylinder or for each wheel, usually measured by a diaphragm or silicone piezoelectric sensor
Silicon piezoelectric sensor measure changes in pressure, acceleration, strain, or force by converting them to electrical energy
Engine and exhaust variables
Includes coolant temperature, engine speed, O2 and NOx levels, spark plug firing timing
Global Navigation Satellite System (GNSS)
uses satellites to determine location
Uses time signals transmitted along a line of sight by radio from multiple satellites
Information available from a receiver
- Absolute position
- Velocity and orientation
- Precise time and synchronised pulse per second
- Raw information that can be used for precise post-processing applications
Uses sensors to perceive road markings, road slope, traffic signs, weather conditions, the state (position, velocity, acceleration, etc.)
Advantages
- Cheap
- Work normally in low visibility and low light conditions
Disadvantages
- Can only be used at low speed, for example during parking
- Shorter field of view and accuracy compared to LiDAR
Image processing sensor
Advantages
- Low-cost
- Implementation is almost entirely in software
Disadvantages
- Implemented as passive sensors, thus must cope with full range of ambient and uncontrolled conditions
- Requires a lot of processing power from the controller, which also increase heat generation