Correlation Based Automatic Registration of Shards on
Vessels for Archaeological Classification
A. E. Uva° *, G. Monno° *
°
CEMeC, Politecnico di Bari, Via Re David 200, 70125, Bari, Italy
dDis, Politecnico di Bari, Via Amendola 220, 70125, Bari, Italy
*
Keywords: Reverse Engineering, Geometric Modelling, Archaeological Classification, Image
Processing.
Aims and Objectives
Due to the lowering of costs and widespread presence of computers, new technologies are being
introduced into those areas where traditionally the only working method has been the “hands-on”
one. This statement can be proved especially in the field of archaeology, since many people
working in this field demand help for time-consuming, boring and repetitive tasks, such as the
classification of archaeological finds. In particular a lot of effort regards the classification of
ceramics. Ceramics, and in particular vessels, are among of the most widespread archaeological
finds. A large number of ceramic shards are found at nearly every excavation and have to be
photographed, measured, drawn and classified.
As one of the Research Unit of a collaborative project on Classification and restoration of
archaeological finds, we are developing an automated registration system for the correct positioning
of a shard (fragment) on vessel (complete ceramic vase) belonging to an archaeological precatalogued class. We use “image registration” techniques to find a correspondence between the
shard and the vessel. Over recent years image registration has emerged as an important topic in
different fields, particularly in medical image analysis. Image registration is concerned with
establishing correspondence between different images or between images and physical space.
The input data for the estimation of the shard shape is a set of points produced by any acquisition
system. For the aims of this paper, all the scanning phases which produce the digitized 3D model
are not considered. We suppose that we are given both different sets of shards points and the
complete set of (synthetic or real) vessel models.
Our method consists of the following steps:
 associate a two-dimensional 8-bit image to the shard, where each pixel value is related to a
specific property choose for comparison;
 associate a larger two-dimensional 8-bit image to the vessel, where each pixel value is
related to the same property;
 find the cross-correlation map of the smaller (shard) image on top of the larger (vessel) one;
 repeat the same steps for all the properties;
 assign a weight to each property and define a “weighted” map for all the cross-correlation
map
 finally find position and rotation of the shard;
Each shard is compared with the synthetic images generated by all the typologies already
catalogued. Our system works principally with the external surface of an archaeological shard,
evaluating the surface curvature characteristics. Other properties as internal surface curvature,
thickness, texture, can be associated to the image for a “better” registration. The technique gives a
sort of “matching” probability because the local peaks in the cross-correlation map define a set of
“best candidates”. The user can also define a minimum matching percentage to avoid bad matching
cases.
Conclusions
We demonstrated the method and give results on both synthetic and real data. Different comparison
criteria can be chosen for the registration of the shard over the vessel category. Results are very
promising, and further steps in this direction are foreseen.
Acknowledgment
This work has been part of a real interdisciplinary project and the successes result from a dynamic
interaction among all the researchers in a broad range of disciplines included in the PRIN –
PROGETTI DI RICERCA DI RILEVANTE INTERESSE NAZIONALE 2001 - ARCHEOCAD
“Archiviazione e restauro di reperti archeologici mediante tecniche CAD-RP”.
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