Time of Flight (TOF) is the time that laser pulse takes to reach the target surface and comes back to the laser scanner’s receiver divided by two. The range to the target is calculated based on the knowledge of the velocity of the pulses in air (propagation medium).
The scan frequency is defined as the number of scan lines per second.
Range gate is the difference between the maximum range and the minimum range the laser scanner is capable of performing range measurements. Instruments with multiple time around capability have no range gate.
The Pulse Repetition Rate (PRR) indicates the (average) pulse repetition rate or frequency with which the laser of the rangefinder emits pulses.
Precision (also called reproducibility or repeatability) is the degree to which further measurements, under unchanged conditions, show the same results. By taking averages over a group of measurements, the precision can be improved, but not the accuracy.
A point cloud is a set of points with coordinate values in a well-defined coordinate system. Beside the coordinates, each point of the point cloud has valuable additional attributes, such as timestamp, amplitude, reflectance, and pulse shape deviation.
Multiple Time Around / MTA is the situation that might occur while scanning when several laser pulses are emitted before the echo from the previous laser pulse reaches the laser scanner. It means that multiple pulses are ‘in the air’ simultaneously. It depends on range to a target and laser pulse repetition rate. Ranging becomes ambiguous, i.e. assignment of the echoes to their corresponding laser pulses is not possible without additional information. This is often referred to as multiple time around (MTA) problem.
The measurement rate gives the average number of measurements per second and depends on the PRR (pulse repetition rate) of the laser and the actual scan range.
Loop closure is needed to start and end a scan in the same place. It is essential that a loop is closed when scanning with a SLAM based system so the sensor can match the features and complete the scan.
Maximum range is the maximum achievable target range up to which the laser scanner can perform range measurements. The maximum range depends strongly on the target characteristics (reflectance), but also an atmospheric visibility and sun light illuminations of the target.
