Introducing True View 635/640
Author: Lewis Graham
Published On: March 12, 2021
In June of 2020 (last June) we introduced the True View 615 and 620. These True View 3D Imaging Sensors (3DIS®) fuse an Applanix APX Position and Orientation System (POS), our dual GeoCue Mapping Cameras and a RIEGL miniVUX-2UAV laser scanner. With a maximum pulse repetition rate of 200,000 outbound pulses per second, this system produces spectacular 3D RGB-colorized LIDAR points at survey grade accuracy.
RIEGL recently introduced the miniVUX-3UAV scanner. Since we have a monthly delivery contract with RIEGL, we were able to receive early shipments of this new scanner. After testing, we integrated this into the 6xx platform, creating the True View 635 (using an APX-15) and the True View 640 (APX-20). A pictorial of the system is shown in Figure 1.
Figure 1: True View 635/640 3DIS
Other than higher point densities in certain operating modes, the miniVUX-3UAV has essentially the same specifications as the miniVUX-2UAV. Thus expect the same RIEGL survey quality network accuracy and precision.
The specifications of the miniVUX-3UAV for pulse repetition rate (PRR) are a bit confusing so I think it is worthwhile to discuss. You may be accustomed to "automotive" designed 360° scanners. These pulse at a constant frequency (say 250,000 pulses per second) and have a scanner rotation rate that can be programmed between a minimum and maximum limit (perhaps 20 to 50 revolutions per second). Thus the distance round the scanner (measured in fractional degrees) between pulses is solely a function of the scanner rotational speed. These scanners emit a fixed number of outbound pulses per second (in our example, 250,000 pulses per second).
The RIEGL systems prior to the miniVUX-3UAV operate in a similar fashion except rather than setting a rotational speed, the step size, in fractions of a degree, between pulses is programmed. This, then, determines the rotational rate of the scanner. If you set a step angle that drives the scanner rotational rate outside its range (10 to 100 revolutions per second, rps, for the 2UAV and the 3UAV, depending on scan frequency) the scanner will adjust the setting to bring it into specification. Are you confused yet?
The miniVUX-3UAV is advertised as having three scanner "frequencies" - 100, 200 and 300 kHz. This might lead you to think this scanner can emit 300,000 pulses per second but this is not the case. The miniVUX-3UAV, when in 300 kHz mode, limits the field of view (FOV) to 120°. You can set this "window" anywhere you like within the scanner's total 360° FOV. While in this window, the scanner can emit a maximum pule rate of 300 kHz (so a pulse every 3.33 micro seconds). If you do the math, you will arrive at 100,000 pulses per second, all within the user defined 120° FOV. The miniVUX-2UAV has a more traditional operational mode, emitting a maximum of 200,000 pulses per second into the total 360° FOV. If we look at a 120° FOV, we compute this as 66,666 pulses per second.
If you did not quite follow the above (I am not sure I did myself!!), you will see that, within a 120° FOV, the miniVUX-3UAV can deliver 33,333 more outbound pulses. This is a significant increase in outbound pulse rate, translating to higher density and, typically, better detection of wires and ground.
A final interesting note. GeoCue 3DIS have been designed from the beginning (with the True View 410) to optimize a 120° FOV. This is why our cameras are set at oblique angles and we default the "on" window our all of our scanners to 120° (you can change this with a parameter file). Thus you can see that the miniVUX-3UAV is a perfect scanner for a GeoCue 3DIS. Coincidence?