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status. The Cyrax had shown strange effects during outdoors 
night-time scans in complete darkness, and surprisingly loosing 
points on some materials. The answer to this was not given 
before the tests took place. The ILRIS-3D had been delivered to 
the Swedish Defence Research Agency in a rush and had not 
been perfectly calibrated by Optech before delivery. 
1.2 Pulsed time of flight laser ranging 
All three systems included in the test make use of pulsed time 
of flight (TOF) laser ranging, probably the most obvious 
method of operating a laser ranging system because the actual 
time of flight is measured directly. Time measurement is 
performed by accurately measuring the time of flight of the 
laser pulse from exiting the laser, reflect off the object, 
returning to the laser, detected by the system and stopping the 
time of measurements. Knowing the speed of light and 
multiplying with half the travel time gives the actual distance to m 
the object. One advantage of using pulsed light is the possibility 
of transmitting a high amount of energy in a very short time, 
which limits the influence of background noise. However, very 
accurate systems require short pulses and going to short pulses 
limits the possible amount of energy in the pulse. The basic 
problem of a TOF laser ranging system is to detect exactly the 
arrival time of the reflected light pulse. A fast time measuring 
device and good signal processing increases distance 
measurement accuracy. Looking at some specific continuos 
wave laser ranging systems the pulsed systems is comparably 
slow due to the relatively low repetition rates for the pulses. 
2. TESTING THE SYSTEMS 
2.1 Testing facilities 
The tests were realised at the Swedish Defence Research 
Agency in Linköping, indoors in a room suitable for testing 
measurements over relatively long distances. Lightning 
condition was uniform for the whole test range, and with the 
light from fluorescent (strip) lighting switch on. The 
temperature and humidity in the room was normal and well 
within the specified limits for the systems used in the tests. The 
air was normal and free from possible dust interfering with the 
measurements. 
2.2 System specification 
Three different high-resolution ground based laser-scanning 
systems were included in the tests: One Cyrax 2500, recently 
acquired by the University of Gavle, one Optech Ilris 3-D and 
one Riegl LMS-Z210. The systems from Optech and Riegl were 
placed at the test disposal by the Laser Systems department at 
the Swedish Defence Research Agency in Linköping. 
As a reference, one reflectorless measuring Trimble 5600 Total 
Station, owned by the University of Gavle, was used. 
2.2.1 Cyrax 2500 
The University of Gavle, Sweden, owns the Cyrax 2500 used in 
the tests. The scanner was purchased late 2001 for use in 
research, especially in the built environment, and in special 
education programmes. 
The basic components of the Cyrax system are the scan head, a 
specially design tripod, a power box, the laptop computer and 
specially design targets. The scan head consist of the actual 
laser scanner and a CCD camera and is connect as a unit to the 
specially design fork mount. The fork mount gives the 
possibilities to easily pan and tilt the scan head in a proper 
position to the targeted area. The Cyrax system is powered by a 
specially designed power box and can either operate from AC 
line power connected to the box our from up to two batteries 
installed in the box. Fully charged two batteries are expected to 
power the system for up to 8 hours. 
The Cyrax uses a pulsing, passively Q-switched green laser that 
scan the object as a cloud of point. This point cloud is a 
representation of actual object’s surface in three dimensions. 
High-speed motorised mirrors deflect the laser pulse as it exits 
the system and sweeps the laser over the object. The Cyrax is 
capable of scanning up 1000 points per second and with a 
single-point position accuracy of ±6 mm. 
With help of a laptop computer connected to the system and the 
Cyrax Cyclone software, the scanner functionality is controlled. 
Furthermore, the Cyclone software provides powerful tools for 
e.g. modelling, meshing and measuring of distances within the 
point cloud. The Cyclone software also includes tools for 
importing of other scanner systems data as well as tools for 
exporting of data. It is also possible to export modelled objects 
to common CAD software, e.g. to AutoCad and Microstation. 
The Cyrax 2500 is the latest version of high-resolution ground 
based laser-scanning systems from Cyra Technologies. 
Development of the Cyrax system was a joint project between 
Cyra Technologies, Los Alamos National Laboratory and 
Massachusetts Institute of Technology (MIT) Lincoln 
Laboratory. The Los Alamos Physics Division developed the 
precise time measuring circuit, Cyra Technologies was 
responsible for developing the software for the system, today 
the software package Cyclone, and MIT Lincoln Laboratory 
developed the laser for the system. Since February 2001 Cyra 
Technologies Inc. is a wholly owned subsidiary of Leica 
Geosystems AG. 
2.2.2 Optech ILRIS-3D 
Swedish Defence Research Agency and its Laser Systems 
department became an owner of one Optech ILRIS-3D system 
in middle of year 2001. The Laser Systems department was one 
of the first buyers of ILRIS-3D system. 
The ILRIS-3D has a distance measuring accuracy close to what 
can be achieved with the Cyrax system. It is twice as fast as the 
Cyrax both much slower than the Riegl system. The system is 
controlled with help of a hand held PDA and measured data are 
stored on ATA flash cards. This eliminates the need for a laptop 
computer during field operation. However, back in the office 
data needs to be downloaded from flash cards to a computer for 
further processing. The system also includes tools for exporting 
of data. 
2.2.3 Riegl LMS-Z210 
Swedish Defence Research Agency and its Laser Systems 
department has been an owner of the LMS-Z210 system for 
some years. The system is a rugged and fully portable sensor 
especially designed for the rapid acquisition of high-quality 
distance measurements under high demanding environmental 
conditions. The LMS-Z210 records not only position and 
intensity values but also a RGB value for each measured point. 
The speed of the system is considerably faster than both the 
ILRIS-3D and the Cyrax, but the distance measuring accuracy