The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
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UAV. In (Sik, 2004) an alternative mini UAV-helicopter is 
presented, which was used as a photogra-phic system for the 
acquisition of ancient towers and temple sites. The helicopter 
should replace high camera tripods and ladder trucks, which are 
uneconomical in cost and time. The helicopter Hirobo & Eagle 
90 has a main rotor diameter of 1.8 m of the main rotor and a 
payload capability of 8.5 kg. The helicopter could carry 
different camera systems like miniature (35 mm), medium (6 
cm x 4.5 cm) and panorama (6 cm x 12 cm) format cameras and 
video cameras. A gimbal was designed as a buffer that can 
absorb noises as well as vibrations. Onboard the system, a small 
video camera is installed too, which is connected to the ground 
station to transmit the images to a monitor in real time. 
Our proposed mapping system differentiates from existing 
UAV-helicopters mainly because of the adopted imaging 
system and the maximum flying height. Indeed we planned to 
employ a model helicopter equipped with GPS, orientation 
sensors, two color digital CCD cameras, working in continous 
mode, synchronisation devices, data transfer unit and batteries 
as power source. In order to keep the system as compact and 
lightweight as possible, digital images and positioning data will 
be stored on-board on memory cards. Figure 1 shows a close-up 
view of our model helicopter, while related technical 
specifications are presented in table 1. 
Figure 1. The model helicopter Raptor 90 v2 
Fuselage length 
1410 mm 
Fuselage width 
190 mm 
Height 
465 mm 
Main rotor diameter 
1580 mm 
Tail rotor diameter 
260 mm 
Total weight 
4.8 kg 
Table 1. Main technical specifications of the Raptor 90 v2 
All the sensors are mounted on a customized platform fixed 
below the helicopter cell between the landing vats. The ima 
ging system is based on a pair of color lightweight digital 
cameras (Panasonic), that will be properly placed on the 
platform and tilted in order to provide an image overlap 
between right and left camera of 70%. The baselength will be 
established according to such requirement and the FOV of the 
cameras. Position and attitude of the model helicopter will be 
provided by a MEMS based Inertial Measurement Unit (IMU) 
with integrated GPS and static pressure sensor, the Mti-G from 
Xsens Technologies (figure 2). This measurement unit has an 
onboard Attitude and Heading Reference System (AHRS) and 
Navigation processor which runs a real-time Xsens Kalman 
Filter providing drift-free GPS positions, 3D orientation data 
and 3D earth-magnetic data. Main specifications of the MTi-G 
are reported in table 2. 
Dimensions 
58 x 58 x 33 mm (WxLxH) 
Weight 
68 g 
Ambient temperature 
(operating range) 
-20 ... + 55 °C 
Operating voltage 
4.5-30 V 
Power consumption 
540 mW 
Table 2. MTi-G technical specifications 
Figure 2. The MTi-G by Xsense Technologies. 
Different approaches have been evaluated for the helicopter 
control system: we found that the better solution, in terms of 
complexity, costs and development times, was to mount the 
control system onboard. In this way, the need to establish a 
bidirectional data communication link between ground station 
and helicopter for the whole flight session can be avoided. 
However we planned to use a radio link in order to manually 
pilot the helicopter during take-off and landing operations. 
Given the size and weight constraints for the guidance system 
components, we adopted an 520 MHz X-Scale Mini processor 
from RLC Enterprises Inc (figure 3). This unit can be 
programmed with C++ language through direct interface with 
the Microsoft Visual Studio suite, allowing us to implement not 
only the code needed for the helicopter control but also for the 
direct georeferencing of acquired digital images. 
Figure 3. The RLC 520 MHz XScale-Mini processor.