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REPLICATION OF MARBLE EXHIBITS USING PHOTOGRAMMETRY AND LASER
SCANNING (OR HOW TO FORGE EXHIBITS).
D. Skarlatos", S. Theodoridou 2 . D. Hennings 3 , S. Ville 4
"National Technical University of Athens, 9 Iroon Polytexniou Str., 15780 Athens, Greece - dskarlat@survey.ntua.gr
"Polyline S.A., 54 G. Gennimata Str., 55134 Thessaloniki, Greece - sofia@polyline.gr
3 IFAM, 12 Wiener Str., 28359 Bremen, Germany - dh@ifam.fhg.de
4 Materialize, Technologielaan 15, 3001 Leuven, Belgium - sven.ville@materialise.be
Commission VI, WG VI/4
KEY WORDS: Automation, modeling, distortion, edge, non metric, archaeological heritage conservation, preservation of artifacts,
replication
ABSTRACT:
The replication (exact copying) of marble museum exhibits using marble powder is being analysed in this paper. Optical and laser
scanners has been used to collect dense point clouds, which form a three-dimensional computer model. This model has been used to
physically reconstruct the object using rapid prototyping techniques. Model of objects from 0.15m up to 1.86m have been replicated
as examples. The procedure and the problems confronted with the solutions given on each case, along with experience gained are
being discussed. Problems concerning accuracy, number of points and formulation of the model are reported. Comparison of the
systems in terms of accuracy, speed and functionality is the main concern of this paper.
Particular reference is being done to the optical scanner. In order to minimize the number of the photographs,
maximize the data collection rate and automate as much as possible the procedure, a slide projector with a grid is being used as the
second camera. The process is depended on machine vision techniques, which automates line extraction and point cloud calculation
thus reducing time, but deteriorating a bit the accuracy. The physical reproduction of Kouros, a 1.86 meter statue is being examined
as an example.
1. INTRODUCTION. 2. SELECTION OF METHODOLOGY
It is quite a common statement to say that the computer
evolution has altered many aspects of our lives, but it is also
true. A few years ago photogrammetry was an exotic
application for precision measurements, open only to experts,
and only a few experts from similar fields were aware of this
scientific application.
The work described in this paper, has been done as part of the
European research programme “Eco_marble”. The main scope
was to create marble copies from marble dust. The main steps in
this procedure were:
• digital modelling of the object using laser scanning,
photogrammetry, or both,
• manipulation of large point clouds, nurb modelling,
processing and finishing of the model
• development of high marble percentage mixtures for use
in a variety of manufacturing machines
• pre processing of the point cloud and preparation for the
rapid prototyping machine
• evaluation of the copies, in terms of material quality,
accuracy and authenticity by the archaeologists and museum
representatives
This paper is mainly concerned with the modeling methods
used, namely laser scanning and optical scanning (or
photogrammetry if you prefer) and their comparison in terms of
accuracy as well as ease of application, density of points and
limitations.
2.1 Review of systems and available techniques
The main aim was to develop methodology for object
modelling. Since this model was to be used for reconstruction it
had to be very dense and very accurate. The accuracy for such
work is being dictated by the manufacturing precision. Most of
them have precision of 150 um, to 100 um, while in some of
them is down to 50um.
Software such as 3D Builder, Photomodeler and Canoma can
offer interesting modelling features in a reasonably priced
package, but their applications are limited by the low
automation level. Hence useful only in gathering a few points
and simple geometry objects. The only work with complex
objects is reported in Yixuan, Z. et al. (1999). It is rather
discouraging in terms of time and man months spend, hence
completely abandoned.
Conventional photogrammetric software with automatic point
collection module was also tested with poor results.
Another interesting case is reported in Scaioni M., et al. (1996).
In this particular paper InduSURF was the commercial package
used. InduSURF is a close range application with the possibility
to automatically collect points in the same reference system
from all images, hence constructing a complete 3d point cloud,
which fully describes the object. The selection of the extraction
areas and the corresponding pairs is being done manually. The
description of the work as well as accuracy for the final point
cloud, are not discussed well enough, but the system is
described with more details by Kloudas (1995). Two interesting
points in the paper are the fact that a random pattern is projected
over the object to provide texture for matching and the RMS of
the bundle adjustment reported, 0.027,0.029 and 0.022 mm in
X,Y,Z respectively.
