Laser Ally Speed LIDAR Operator Guide
Digital Ally, Inc.|Doc. 30157 Rev 12
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Appendix A – Cosine Effect
The term “Cosine Effect” as typically used in law enforcement speed
measurement, refers to the reduction of a vehicle’s measured speed
using Radar or Laser systems as compared to the actual vehicle
speed when targeting the vehicle at an angle. The diagram below
shows the line “V” as the vehicle’s travel direction and the LIDAR
operator’s line of sight “O” to the target vehicle. The angle between
these two lines is labelled theta ”Θ”. Motion of the vehicle along
“Line V” is projected onto the LIDAR operator’s line of sight “Line O”.
Using standard trigonometry, this projected motion can be shown to
be:
ΔO = ΔV x COSΘ
ΔO
ΔV
Θ
Line V
Line O
d
