Global Positioning System Reference
In-Depth Information
There are several advantages to utilizing a UAV. One of the most important advantages is
that it is unmanned and therefore can fly over dangerous zones. This advantage suits the
purpose of direct geo-referencing in this study. Direct geo-referencing does not require that
ground control points have accurately measured ground coordinate values. In dangerous
zones, it is impossible to set control points, unlike the case in normal aerial surveys. The
addition of this direct geo-referencing method from a UAV could be an ideal tool for
monitoring dangerous situations. Therefore, this UAV-based mapping system is perfectly
suited for disaster areas such as landslides and floods, and for other applications such as
river monitoring.
Weight
330kg
Payload
100kg
Motor
83.5 hp
Main rotor
2 rotors, diameter 4.8m
Tail rotor
2 rotors, diameter 0.8m
Operational
3km or more
Flight time
1 hour
Ceiling
2,000m
Table 4. Specification of RPH2
5.1.1 UAV based system
All the sensors are tightly mounted under the UAV to ensure that they have a constant
geometric relationship during the measurement. The digital cameras and the laser scanner
are calibrated to estimate the relative position and attitude. Moreover, all sensors are
controlled by a laptop PC and are synchronized by GPS time, one pulse per second. Finally
the sensors are set, as shown in Figure 10.
5.1.2 Digital 3D modeling
During measurement, the platform, including all of the sensors, is continuously changing its
position and attitude with respect to time. For direct geo-referencing of laser range data, the
hybrid positioning data are used. There are two coordinate systems; the laser scanner and
the hybrid positioning, WGS84 (World Geodetic System 1984) based on GPS and the BBA
data. It is necessary to transform the laser scanner coordinate into the WGS84 coordinate by
geo-referencing. Geo-referencing of the laser range data is determined by the 3D Helmert's
transformation, which is computed by the rotation matrix and translation matrix with the
hybrid positioning data and calibration parameters as offset values, as shown in Equation
(3), for calibration by the laser scanner. The offset values from the laser scanner to the digital
cameras in the body frame are already obtained by the sensor calibration. Geo-referencing of
laser range data and images is done directly.
Figure 11 shows the 3D point cloud data that are directly geo-referenced by the hybrid IMU
data. In this research, the WGS84 is used as the base coordinate system for the 3D point
cloud data. The UAV-based system in this research utilized a landslide survey by
Search WWH ::
Custom Search