Cosine Error
Definition
The under-reading of true speed that occurs when the radar or LIDAR beam is not perfectly aligned with the vehicle's direction of motion. Always works in favour of the driver, never against.
- Cause
- Beam not aligned with vehicle's direction of travel
- Effect
- Under-reads true speed
- Direction of bias
- Always favours the driver
Common questions
Why can't cosine error ever make a reading too high?+
The trigonometry of the effect means the measured component of velocity along the beam is always less than or equal to the vehicle's actual speed, so the error can only reduce the reading, never inflate it.
How is cosine error relevant to challenging a speed measurement in court?+
Because the effect only helps the driver, a defence argument based on cosine error would need to show the reading was actually too low to support the charge, not that it overstated speed, which limits how the error is typically used in disputes.
Related terms
- ANPR
- Automatic Number Plate Recognition. A camera plus OCR pipeline that reads vehicle number plates at speed and logs the plate, timestamp, and...
- Calibration Cycle
- The periodic re-certification of a speed-measurement device against a traceable reference, usually annually for radar guns and every six months for LIDAR....
- Doppler Effect
- The change in observed frequency when the source and the observer move relative to each other. A radar gun emits a known...
- FASTag-ANPR Fusion
- Indian highway tolling pairs RFID FASTag reads with ANPR cameras at every electronic toll gantry, creating a national vehicle-position log that investigators...
- Time-of-Flight (LIDAR)
- A measurement principle where the device emits short laser pulses and times how long each pulse takes to return. Multiple pulses over...