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EXPLORATIONS INTO THE BEHAVIOUR OF THREE DIFFERENT 
HIGH-RESOLUTION GROUND-BASED LASER SCANNERS 
IN THE BUILT ENVIRONMENT 
M. Johansson 
Gàvle GIS Institute, University of Gàvle, SE-80176 Gàvle, Sweden - mjj@hig.se 
KEY WORDS: Laser scanning, Close Range, Terrestrial, Accuracy, Performance 
ABSTRACT: 
Today, high-resolution ground-based laser scanning has entered the field of distance measurements for documentation of objects. 
However, the documentation of high-resolution ground-based laser scanning with respect to its specific characteristics and behaviour 
is still in its early stages. The aim of present work was to contribute to the evaluation and documentation of such systems. Three 
systems was included, the Cyrax 2500, Optech ILRIS-3D and the Riegl LMS-Z210, all based on the pulsed time of flight (TOF) 
laser ranging technique. The systems distance measurement accuracy was investigated, the systems possibilities to resolve test 
objects representing the built environment was briefly evaluated and different materials influence on the results was looked into. 
Modelled surface precision was found close to vendor specifications; still some points deviated relatively far from modelled 
surfaces. For Cyrax with a modelled precision of 2 to 4 mm maximum errors of 9 to 20 mm was found. ILRIS-3D with a modelled 
precision of 8 to 12 mm showed maximum errors from 35 to 65 mm. Due to system limitations a coarser scanning resolution was set 
for the LMS-Z210. A modelled precision of 20 mm and maximum errors of 52 to 75 mm was found for the LMS-Z210. When 
comparing distances measured with the systems to “true distances”, Cyrax was found to be within 2 mm of the true values over a 
range of 85 meter. ILRIS-3D deviated 2 to 22 mm from the “true distances” and the LMS-Z210 deviated 7 to 24 mm from “true 
distances”. For all three systems strange effects along edges of objects was found. For the ILRIS-3D the edge effects was relatively 
large compared to the other systems. The edge effect was also found to limit the possibility to resolve small objects and objects close 
to each other. Cyrax was found to resolve details best. The Cyrax system showed problems in measuring of objects with low 
reflectivity. However, major dropout of points only occurred beyond the recommenced maximum range of 50 meter. 
1. BACKGROUND AND THEORY 
1.1 Background 
This work is a first contribution from the Gavle GIS Institute in 
its exploration into the behaviour of high-resolution ground- 
based laser scanners and its use in the built environment. 
Three different laser scanners are included in the tests: One 
Cyrax 2500 from Leica Geosystems, recently acquired by the 
University of Gavle, one Ilris-3D from Optech and one LMS- 
Z210 from Riegl. The Swedish Defence Research Agency and 
its Laser Systems department in Linköping provide the systems 
from Optech and Riegl. All three systems measure distances 
with help of the time-of-flight distance measurement technique. 
As a reference, one very accurate reflectorless measuring 
geodetic surveying instrument, a Trimble 5600 DR200+ total 
station, will be used. 
The tests focus on the scanner’s behaviour in different 
important situations for documenting the built environment. 
The focus is not on a direct comparison of the scanners. Instead, 
the focus is in trying to find the unique characteristics for each 
scanner, and, although the scanners have different 
specifications, finding possible similarities and differences 
between the different scanner behaviours in problematic 
situations. 
In general, the tests can be divided into three parts. The first 
part covers the systems distance measuring accuracy; the 
second part tests how well the point clouds actually represents 
reality; and the third part consists of tests on how different 
objects reflectivity influence the performance of laser scanners. 
Activities such as detecting edges, scanning through small 
openings, recording from extreme angles of incidence and 
measurements on materials with different reflectivity will be 
examined.. For all these situations or, combination of situations, 
it is important to understand where possible erroneous points 
can be found to be able to evaluate and make use of the 
resulting point-clouds in a comfortable way. 
Two test objects have been specially designed and built for 
evaluating laser-scanning results for problematic areas in the 
built environment. One of the test objects consists of parallel 
mounted plates, approximately 60 by 40 centimetres in size, 
with fixed distances between, and with cut-outs of known 
geometrical figures in the front plate. The plates are made of a 
high reflective material and all measures, including size of cut 
outs, are within sub-millimetre accuracy. This object is 
specifically designed to give answers to the behaviour of the 
different scanner results from detecting edges and scanning 
through small openings. To be able to evaluate different angle 
of incidences and surface structures a one cubic meter box has 
been built. Pasted on the sides are different surface materials 
and the box is mounted on a centre axis to allow the possibility 
to rotate it. In addition, the top of the box is equipped with 
points of attachment for specific registration spheres, and for 
targets of different sizes for tests of distance measurement 
accuracy. A target of materials with different reflectivity will 
also be used in the tests. 
Besides information about how the different tests were realised, 
and the results from the tests obtained, the goal is to present 
possible methods to avoid “unwanted” data, or identifying were 
“unwanted” points can be found in the point-clouds. 
Though the systems before the tests took place had been used in 
research and for educational purposes as well as in real world 
“production” projects, there were some doubts about their