TOWARDS AN OPERATIONAL DIGITAL VIDEO PHOTOGRAMMETRIC SYSTEM FOR 3-D MEASUREMENTS
E. Tournas, Postgraduate Student
Dr. A. Georgopoulos, Assistant Professor
Laboratory of Photogrammetry
National Technical University of Athens
Greece
Commision Il, Intercommission Working Group I/II
KEY WORDS: Digital Video, 3-D Measurements, Hardware, Software, Industrial Application
ABSTRACT
In this paper the first attempt for developing a complete and operational photogrammetric system for determining the trajectories
of moving objects in space using digital video is described. The system is based on a Personal Computer and consists of off-the-
shelf hardware in order to enable the stereoscopic observation. The input data is a sequence of synchronised image video frames
acquired with two video cameras. It is usually assumed that the changes in a scene are due to object motion and the two cameras
are stable. The system extracts masks of moving targets in order to recognise them, thus determining 3-D coordinates of the
observed points and subsequently producing the motion characteristics of the object.
The integration of the system involves development of specialised software. Firstly camera calibration is performed on both
cameras with the help of a self calibrating least squares bundle adjustment solving simultaneously for all the unknown parameters.
Secondly the relative and absolute orientations are performed with the help of a two camera triangulation algorithm, while the
image coordinates of the observed points are determined automatically by using a cross correlation algorithm which matches the
observed premarked targets with a predefined target template. Stereoscopic vision is ensured with the help of the CrystalEyes
system applied on resampled data, which form a pair of epipolar images. Finally specialised software has been developed in order
to animate and view stereoscopically image sequences, perform 3-D measurements and support interactive point and line drawing.
In order to thoroughly investigate the suitability of the methodology an application involving analysis of seismic movements of
scaled models was performed. Experiments have been carried out in the Laboratory of Earthquake Engineering of NTUA, in order
to monitor the movements in space of an ancient Parthenon pillar model of 1:3 scale. The results of this practical application are
also briefly presented and discussed.
1. INTRODUCTION
The determination of 3-D positions of moving objects is a
highly important subject in many industrial processes and
research areas. Vision based systems combining the principles
of machine vision and digital photogrammetry have great
potential for solving such kind of measurement problems. In
the following the first approach for developing a digital
stereoscopic video system for determining the trajectories of
moving objects in space will be described.
The main aim of the system developed was to provide a way
of monitoring, recording and determining the, usually
unpredictable, motion of objects under seismic action. The
results should satisfy certain tight accuracy limits, while the
cost should, as always, be kept to a minimum. At the same
time simplicity and applicability was of high significance.
Since rapid and unpredictable movements ought to be
recorded, the use of video as the only suitable data capture
means was inevitable. When digitised, this would produce a
huge amount of electronic data, whose storage and processing
would be very difficult. Hence the need arose for developing
a custom made system in order to be able to metrically exploit
the available data. The development of the system called for
specialised software in order to exploit the off-the-shelf
hardware which was used. The system in its present stage of
development consists of a 486 PC with a 17" monitor capable
of producing refresh rates at a frequency of 120 Hz and the
necessary hardware for the stereoscopic observation
(Figure 1).
Figure 1
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996
