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TECH

TALK

RD-M1 LiDAR Road Scanner
By Shane Jakubec, GdB Geospatial
LiDAR (Light Detection and Ranging) technology is not
new to surveying. Aerial, terrestrial and mobile LiDAR
platforms have been deployed in the field for decades
from design to construction applications. However, as the
technology matures, the abundance of platforms offered by
manufacturers has increased and that includes the increasing
introduction of low-cost LiDAR platforms. This in turn
has expanded the user base in which these systems may be
deployed. In fact low-cost LiDAR scanners are even being
put into mobile phones. A quick search on YouTube can
reveal several videos showing the limited application even
these scanners can play in surveying. are informed by the two surfaces loaded into the paver. By
using this method, potential errors in the elevation readings
Traditionally mobile LiDAR platforms have cost several from the GNSS receivers on the paver can be eliminated
hundred thousand dollars, leaving them out of reach for as these are only being used for horizontal position where
smaller surveying and construction firms. However, as has typically the errors are much smaller.
been the case with other LiDAR platforms, the price of
these have fallen as well. One such system that has been on The main positional data for the RD-M1 comes from the
the market in recent years is the TopCon RD-M1 LiDAR GNSS receiver on the top of the unit, a Hiper SR. This
road scanner. This system is comprised of four main sensors: data is coupled with the information from the IMU, the
the LiDAR scanner, the GNSS (Global navigation satellite wheel encoder as well as static information from a base
system) receiver, the IMU (Inertial measurement unit), and station to refine the trajectory of the vehicle. The RD-M1
the wheel encoder. The wheel encoder is a sensor that mounts achieves higher than normal GNSS accuracies by requiring
to the lug nuts of the driving vehicle to count the rotations of several passes over the same area, typically three to four. The
the wheel in order to compensate the GNSS receiver in areas process is comparable to taking a several second shot with
of low GNSS quality. The RD-M1 differs from most mobile a GNSS receiver on a rod. The readings are averaged for a
LiDAR platforms in that the LiDAR sensor is pointed directly more accurate reading than a single shot could provide.
at the ground in the rear of the vehicle. This is because the The RD-M1 is quickly mounted to the rear of a vehicle,
RD-M1 was designed to be used in machine-controlled 3D typically a truck. The scanner is then driven up and down
paving workflows, although it’s use can be extended to other the lanes of a road to capture the road surface at speeds as
applications including design topographies. fast as highway speeds. Several miles of road can be scanned
in a couple of hours. The ease of use and speed of capture
The RD-M1 road scanner has been adopted by many
contractors to assist in 3D paving projects. It was particularly allows for quick turnaround of existing pavement surfaces
designed to support mill and fill jobs where the existing allowing for a seamless workflow between pavement lifts.
surface can be scanned, and with some minor editing to The RD-M1 is an example of how new technologies are
the scanned surface, the pavement can be replaced back increasingly becoming accessible to new users and disrupting
but with a smoother profile. TopCon calls this workflow long established workflows.
their SmoothRide™ Solution. Paving in the SmoothRide™ Of course, the RD-M1 is no substitute for a well-controlled
workflow involves giving the paver two surface files to mobile scan. However, many applications don’t need
work with. One surface file is extracted from the scan of millimeter accuracies. As surveyors it is our role to inform
the existing pavement, and the other is the design grade. contractors what tools they may need for their job. The RD-
The horizontal location of the paver is controlled by GNSS M1 offers a solution to keep costs low while providing a
receivers on each side of the paver screed, while the elevations final paving product that exceeds quality expectations.

EMPIRE STATE SURVEYOR / VOL. 57 • NO 6/ 2021 • NOVEMBER/DECEMBER 21