Calibration Methodology for Laser Scanner External Parameters
Masahiko Nagai, Ryosuke Shibasaki, Dinesh Manandhar
Center for Spatial Information Science, The University of Tokyo
Cw-503, IIS, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan
Tel: +81-3-5452-6417 Fax: +81-3-5452-6414
E-mail: nagaim@iis.u-tokyo.ac.jp
ABSTRACT
In order to present a space in details, it is indispensable to acquire 3D information. Laser
scanner is one of the most effective tool for acquiring 3D information. For 3D measurement by a
laser scanner, it is necessary to conduct sensor calibration to know the relative position and
attitude against other positioning sensor. However, quick and handy method of a laser scanner
calibration did not exist, because laser beam is invisible for human eyes and it is very difficult to
see whether the center of a laser beam exactly hit upon control points. In this study, we propose
a new method of calibration to determine the external orientation parameters of a laser scanner
using a solar cell connected to an earphone for laser beam detection. If the laser beam hit the
solar cell, beep sound let us know it does. By finding out the location of maximum sound level,
the center of laser beam can be located for calibration even though laser beam is invisible.
Through the experiment with this method, it is concluded that the external orientation
parameters of laser scanner can be determined, and it helps to combine a laser scanner with a
digital camera or IMU easily for simple 3D measurement.
1. INTRODUCTION
A lot of researches are conducted for acquiring 3D spatial information by using
photogrammetric methods. With this method, 3D information is extracted by stereo matching,
but this method is very difficult to automate in certain measurement conditions because of
shadows or occlusion of features. On the other hand, a laser scanner can directly measure 3D
shape of a target feature automatically. Laser scanner has been successfully applied in many
applications. Furthermore, with the development of technology, a laser scanner become cheaper.
Nowadays, some laser scanners can be purchased in few thousands of US dollars. That is, a laser
scanner can be used for 3D measurements easily.
In case of 3D measurement by a laser scanner, it is indispensable to conduct external calibration
against other positioning sensor (Manandhar and Shibasaki, 2002). However, a laser beam of a
laser scanner is invisible, that makes it impossible to directly apply such control points as used
for the calibration of CCD camera. Thus, it is difficult to check whether a laser beam hits on
targets or not. In this research, a new methodology for the external orientation of laser scanner
using a solar cell is proposed.
