The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008
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mentioned processing chain are recapitulated. The paper
concludes with an outlook on ongoing and future development
steps.
2. UNMANNED AERIAL VEHICLE SYSTEMS
2.1 Overview
A rapid development of unmanned aerial vehicle systems has
taken place in the last few years. Today, a wide variety of
different UAV systems exists on the market. The European
Association of Unmanned Vehicle Systems (EUROUVS) has
drawn up a classification of the different system platforms. In
(Bento, M. 2008) the current EUROUVS classification is
presented and a good state of the art overview is given.
Category
Max. Max. Endurance Data
Take Off Flight Link
Weight Altitude Range
Micro
Mini
< 5kg 250m lh < 10km
< 30kg 150-300m <2h < 10km
Table 1: Classification of mini and micro UAV systems
This paper is focused on mini and micro UAV systems. Table 1
shortly recapitulates the technical specifications of these two
UAV categories, again based on the current classification by
UVS International. Most of the mini or micro UAV systems
available today integrate a flight control system, which
autonomously stabilises these platforms and also enables the
remotely controlled navigation. Several systems additionally
integrate an autopilot, which allows an autonomous flight based
on predefined waypoints. These flight control systems are
typically based on MEMS (Micro-Electro-Mechanical System)
IMU systems, navigation-grade GPS receivers, barometers, and
magnetic compasses. The different sensor observations are
usually integrated to an optimal flight state using an EKE
(Extended Kalman Filter), which is subsequently used in the
flight controller. For mapping applications, it is also possible to
use this flight control data to geo-register the captured payload
sensor data like still images or video streams. However, as a
result of the utilisation of low-weight and low-cost flight
control sensors, the achievable geo-referencing accuracy is
strongly limited.
2.2 Microdrones md4-200 platform
Figure 1: Quadcopter micro UAV (microdrones md4-200)
system (left) with portable ground control station (right)
For the prototype solution presented in this paper we use the
micro UAV platform microdrones md4-200 which is illustrated
in Figure 1. The following listing contains a short overview of
the technical specifications of the platform and of the sensors
used for capturing video streams and flight control data.
Platform
UAV category:
max. take off weight:
max. payload:
endurance:
Sensors
GPS receiver:
IMU:
magnetic compass:
barometer
video camera (payload): non-metric / PAL output
resolution: 640x480 pixels
Flight attitude accuracy (After sensor data fusion)
position: 2.5 m CEP
altitude: 5 m SEP
roll and pitch angle: 1-2°
yaw angle (Heading): 3-5°
Notable is the low attitude accuracy of the integrated flight data,
especially the heading accuracy which is approximately three
times lower than that in roll and pitch. This has a direct
influence on the achievable video geo-referencing accuracy,
especially for large image to object distances. Details of the
implemented sensor data fusion approach are presented in
(Meister et al., 2007). The systems platform includes an
analogue data link between platform and ground control station
for video- and flight control data transmission. The flight
control state consisting of position, velocity and attitude of the
platform together with a time stamp in UTC is transmitted with
4-5Hz. Due to the restricted payload of only 300g, it is not
possible to use a video camera with high quality optics or a
genlock capability.
3. VIRTUAL GLOBES
3.1 State of the art
Different web-based 3D geoinformation services based on
virtual globes are available today. Google Earth and Microsoft
Virtual Earth are only two prominent examples. Most of the
available virtual globe technologies have the possibility to
integrate large amounts of geospatial content, like terrain
models, orthomosaics, 3D objects, points of interest or
multimedia objects. Many solutions have an excellent ability to
stream very large volumes of geodata.
Among the shortcomings of virtual globe services are the often
outdated geodata contents. However, for many possible
application scenarios like real-time surveillance or decision
support applications the availability or integration of up-to-date
or even live imagery data is crucial. Furthermore, with most
virtual globes, it is not known which underlying earth model is
implemented. However, for an accurate geospatial content
integration the knowledge of the used geodetic global reference
system(s) is crucial. Overviews of available virtual globe
technologies can be found in (Thalmann, 2007) or (Bleisch and
Nebiker, 2006).
micro (quadcopter)
0.9 kg
0.3 kg
20 min
u-blox (navigation grade -
pseudorange processing)
6DOF MEMS based
three-axis sensor