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7.4 Last-hit mode
The Quarryman Pro measures distances by sending a pulse of laser energy out to a target and timing how long it
takes the pulse to reach the target, reflect from it, and return to the receiving optics.
In some conditions, the pulse can be reflected off particles in the air between the laser and the intended target: for
example, if the instrument is in a particularly dusty environment, if there is mist in the air, or if it is snowing.
In these conditions, turn on
Last-hit
mode. In this mode, the laser will try to filter out the false readings from particles
in the air by concentrating on the pulses which have taken the longest time to return to the laser. These will generally
be the pulses that have penetrated to the targeted surface, rather than those which have been reflected by the
airborne particles.
However, if the conditions are so bad that very few pulses are penetrating to the intended target, then
Last-hit
mode will not be able to help. In this case, you may need to postpone the survey until the weather improves or the
dust clears. Alternatively, you may be able to move the instrument to a position where there is a clearer view of the
scene to be scanned.
Note that you should never use
Last-hit
mode to shoot to reflective targets, as erroneous ranges can result. It is
recommended to leave
Last-hit
mode off unless it is specifically required.
Chord value
selected to
determine scan
line spacing
Figure 46 FastScan with Chord increment selected
