Kunal Amarnani
L02 – Dr. Smith
Helicopter Group
Use of Motion Capture in an Autonomous Aerial Vehicle
Introduction
Motion capture is “involves measuring an object's position and orientation in
physical space, then recording that information in a computer-usable form” [1]. It refers
to the process of using several cameras to record the movement of objects and translating
the objects motion onto a 3D virtual environment. This paper focuses on the use of
motion capture cameras to record the movement of an aerial vehicle in a large room. The
data received can then be used to control the movement of the vehicle.
Commercial Applications of Autonomous Vehicles
The demand for autonomous aerial vehicles (such as helicopters) has seen an
increase over the past few years, as they have become an important part of military
exercises. The use of Unmanned Aerial Vehicles (UAVs) reduces the risk to human life
especially during scouting missions. UAVs have been successfully used in the Iraq war
and even in the Katrina rescue effort. However, there still exists a lot of difficulty in
implementing and coordinating multiple UAVs at the same time. Using a motion capture
system to control the UAVs in a controlled environment will enable researchers to
explore multivehicle coordination much further [2].
Technology behind Motion Capture Cameras
In order to capture the movement of the vehicle, it must first be outfitted with
reflective dots. The camera can the follow these dots and triangulate the respective
position of the dots onto the virtual 3D environment.
The cameras consist of a video camera, a strobe head unit, a lens, and an optical
filter. The strobe head unit emits a distinct wavelength of light that is reflected by the
surface dots located on the vehicle. The light is emitted as a bright flash that is timed to
coincide with the opening of the camera’s shutter. This reduces the interference from
outside sources of light. The lens captures the light reflected off the surface dots and
forms a focused image on the camera’s sensor plane. In order to remove other
wavelengths of light other than those emitted by the LEDs in the strobe head unit, each
camera has an optical filter. The filter allows in low-level wavelengths like those emitted
by the strobe head unit (e.g. near infra-red light or infra-red light).
In order to gain an accurate portrayal of the vehicle in a 3D environment, several
cameras are needed to triangulate the relative position of each dot in the room. These
cameras must be evenly spaced around the room in order to maximize their efficiency.
Implementing the Motion Capture System
The system is very hard to build from scratch as it requires a high resolution
camera with very shutter speed as well as several infrared emitting diodes that are in
perfect sync with the shutter.
However, there are several commercial systems readily available for purchase,
including the VICON MX. The system comes with several high resolution cameras, all
the hardware controllers required to link the cameras up to the computer, as well as the
required software to analyze the data. Once the motion capture system has been set up,
and the relative position of the vehicle in the room has been found, the vehicle can then
be moved autonomously by the computer using its current position and its required
destination.
[1]
Scott Dyer, Jeff Martin, John Zulauf, "Motion Capture White Paper," [Online
Document], 12 Dec 1995, Available: http://reality.sgi.com/employees/jam
sb/mocap/MoCapWP_v2.0.html
[2]
J. How, “Raven: Testbed for autonomous UAVs,” Aero-Astro, No. 4, 2006-2007
[3]
Maureen Furniss, “Motion Capture,” [Online Document], 19 Dec 1999,
Available: HTTP://web.mit.edu/comm-forum/papers/furniss.html
[4]
Vicon MX Hardware System Reference, Rev 1.6, Vicon, Oxford, UK, 2007
[5]
Vicon Products Glossary for Vicon MX and V-series systems, Vicon, Oxford, UK,
2007
[6]
Vicon MX [Online]. Available: http://www.vicon.com/products/viconmx.html