Documentation and computer reconstruction strategies in the study of architecture at the sanctuary of Poseidon at Kalaureia, Greece

Abstract

In the recording of the progress of the excavations and architectural features at the sanctuary of Poseidon at Kalaureia special emphasis has been placed on the use of current digital technologies. Three-dimensional site scanning was ruled out due to high costs and it has been largely replaced by extensive use of up to three total stations. In the recording of architecture the total stations are used to directly 'draw' the features with laser beam. Effective use of the laser requires frequent changes in the position of the instrument which is made possible by an extensive network of fixed points over the large site. Recording the architecture principally as lines has the added benefit of making the production of site plans and 3D reconstructions quicker. Due to the detailed measurements of the archaeological features it is also possible to present 3D digital elevation models (DEMs) of the various stages of the excavations. Further details can be added to the 3D models by draping actual photographs over the DEMs. The terrain models and recorded ancient features can be integrated with the reconstructions to display the basis of the architectural interpretations.

Full text

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International Congress „Cultural Heritage and New Technologies“ Vienna, 2008
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Documentation and computer reconstruction strategies in the study
of architecture at the sanctuary of Poseidon at Kalaureia, Greece
Jari PAKKANEN
Royal Holloway, University of London
Abstract: In the recording of the progress of the excavations and architectural features at the
sanctuary of Poseidon at Kalaureia special emphasis has been placed on the use of current digital
technologies. Three-dimensional site scanning was ruled out due to high costs and it has been largely
replaced by extensive use of up to three total stations. In the recording of architecture the total stations
are used to directly ‘draw’ the features with laser beam. Effective use of the laser requires frequent
changes in the position of the instrument which is made possible by an extensive network of fixed
points over the large site. Recording the architecture principally as lines has the added benefit of
making the production of site plans and 3D reconstructions quicker. Due to the detailed
measurements of the archaeological features it is also possible to present 3D digital elevation models
(DEMs) of the various stages of the excavations. Further details can be added to the 3D models by
draping actual photographs over the DEMs. The terrain models and recorded ancient features can be
integrated with the reconstructions to display the basis of the architectural interpretations.
Keywords: Greek architecture – Kalaureia, Greece – Sanctuary of Poseidon – digital documentation
– three-dimensional reconstruction
Introduction
The Kalaureia Research Program – the Sea, the City and the God is a multi-disciplinary project hosted
by the Swedish Archaeological Institute at Athens and funded by the National Bank of Sweden
Tercentenary Foundation (2007–2012).
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The project combines three different strands of inquiry into an
important sanctuary of ancient Greece: archaeological investigation, study of the local religion and its
contribution to understanding Greek religion in general, and exploration of the impact of the
archaeological remains on the local community. The specific responsibility of the author of this paper
is to conduct research on the architectural remains of the sanctuary, and besides basic publication of
the buildings, also to produce a computer model of the site (for an overview of the project, see
www.kalaureia.org; PENTTINEN et al. forthcoming). The new research programme is directly linked to
the Swedish excavations carried out at the site since 1997 (WELLS et al. 2003; WELLS et al. 2005;
WELLS et al. 2006–2007).
Poros is located in the south of the Saronic Gulf, and it comprises two separate islands: Spheria in
the south, where also the modern town and harbour of Poros are located, and Kalaureia, the larger
northern island with the homonymous archaeological site. The sanctuary is located on the saddle
between the hills of Vigla and Agios Ilias at the height of some 190 m above the sea level. The ancient
harbour was located in the Bay of Vayonia to the north of the site.

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International Congress „Cultural Heritage and New Technologies“ Vienna, 2008
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With a temple and five major subsidiary buildings, the site is among the most important sanctuaries in
the Saronic Gulf (Figs. 1 & 2). As to its architectural importance it is on par with other large
sanctuaries of Greece. The sanctuary is best known as the death-place of the orator Demosthenes,
who sought asylum
Fig. 1 – General view of the sanctuary from southwest in 2008. Attica is faintly visible in the background (J. Pakkanen).
Fig. 2 – General plan of the archaeological site with named buildings inside the sanctuary (J. Pakkanen & E. Savini).

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there in 322 BC. He was pursued by the Macedonians after the capture of Athens, and with nowhere
to escape he committed suicide by taking poison (STRABO 8.6.14; PLUTARCH, Vit. Dem. 28–30).
The foundations of the buildings are mostly what remains of the temple, stoas and the entrance
propylon: there is very little standing higher up than the ground level (Fig. 1). The fragmentary nature
of the architectural remains provides a very interesting scholarly and methodological challenge: how is
it possible to study the ancient built environment in a case where the majority of the building material
has been systematically dismantled and reused away from its original context? One way of answering
the question is to carry out a thorough comparative study of related buildings and sanctuaries in the
neighbouring regions, and the new excavations are already bringing into light large numbers of
fragments and also some more complete architectural blocks.
Since there are no standing structures, the site has attracted little attention from scholars of Greek
architecture. As part of the excavation campaign in 1894 by Wide and Kjellberg their architect, Sven
Kristenson, recorded plans of the buildings, and in 1930s the German scholar Gabriel Welter carried
some further studies on the architectural remains. Despite the use of the sanctuary as a quarry for
building material, previous studies at the site have managed to establish the majority of the principal
features and dimensions of the building plans (WIDE & KJELLBERG 1895; WELTER 1941).
Documentation strategies
Current digital survey technologies have been widely employed in the recording of archaeological
material from the start of the excavations at the site in 1997: the employed surveying, global
positioning system (GPS), photogrammetry and geographical information system (GIS) strategies are
described in detail by Emmanuel Savini in WELLS et al. 2003, 129–135. The role of current
technologies has been further emphasised in the new research programme started in 2007, though
three-dimensional site scanning was ruled out at the planning stage of the project due to high costs.
One of the principal aims of this paper is to demonstrate that detailed surveying of the architectural
remains with a total station can still be used as a cost-effective alternative for building precise 3D
models of both the in situ and displaced building blocks and fragments. Perhaps the main advantage
of surveying with a reflectorless laser total station is that the interpretation of what is recorded and how
it is done is made directly in the field and not in the post-processing phase (Fig. 3).
H. Eiteljorg has criticised the use of laser in archaeological surveying as follows: “Modern total stations
no longer require the use of a target; they can take a direct reading from nearly any surface. This can
reduce the surveying “crew” to [a] single person. Note the trade-off, however, when using a total
station without a target. The operator is obliged to pick points to be surveyed by looking through the
instrument telescope from some distance. Very fine discriminations simply cannot be made from ten or
twenty meters away” (EITELJORG 2007, 199). However, these problems are easy to avoid by keeping
the instrument close to the observed blocks and in normal circumstances using the laser pointer
instead of looking through the telescope. Nearly all the points at Kalaureia have been recorded within
five meters of the total station and with some practice it is possible to learn to read where the centre of
the laser pointer is in relation to the intended measurement target on the building block without

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checking the crosshairs of the telescope (Figs. 3 and 4). Wearing laser enhancement glasses
increases the visibility of the pointer so that it is well perceptible also in the strong midday sun, and the
major benefit of working mainly with the pointer is that the time needed to adjust
Fig. 3 – Schematic representation of survey principles and terminology using reflectorless laser total stations (J. Pakkanen).
Fig. 4 – Total station survey of Building A in October 2008 (J. Pakkanen).
the telescope is entirely eliminated allowing clearly faster rate of shooting points. Keeping the distance
between the architecture and the total station as small as possible does require several changes in the
position of the instrument during the day. An extensive network of laser targets over the large site has
made it possible to freely relocate the total station with minimal loss of working time and also into an
optimal place in relation to the documented blocks without being tied to a limited number of fixed
station points (Fig. 5). A typical change of instrument location takes now less than fifteen minutes, and
the standard deviations in the instrument co-ordinate position using five laser backsights is normally

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1 mm or less. We have been able to obtain a usual rate of 300–500 points per hour at Kalaureia using
this method varying mainly due to the type of documented object.
Fig. 5 – Network of fixed points used as backsights for free positioning of the total stations (J. Pakkanen).
The architectural features are principally recorded as lines (Fig. 6). The preserved surfaces of the
blocks are documented in detail, and the surveyor makes the decision how precisely to shoot the
broken surfaces and modern graffiti: we have opted to do rather precise recording also of the cracked
edges and centre lines of the graffiti. The method can effectively be described as directly ‘drawing’ the
blocks in 3D with the total station. Recording the blocks principally as lines makes the production of
architectural plans straightforward: Fig. 7 presents a direct ‘raw data dump’ of the AutoCAD plan view
as it is documented on the total station. For a final plan it is only necessary to modify the line widths,
types and colours to reflect differences in the recorded features. In addition, data recorded as lines are
very useful in faster production of 3D surface

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Fig. 6 – Isometric view of Building A as recorded with total station (J. Pakkanen).
Fig. 7 – Plan view of the raw data on Building A as recorded with a total station (J. Pakkanen).
Fig. 8 – On the left an automatically generated 3D model of the architectural and current terrain features of Building D and on
the right the same model with an AutoCAD reconstruction superimposed on the remains (J. Pakkanen).
models of the preserved features and also of 3D reconstructions in AutoCAD. The wireframe model of
Building A presented in Figs. 6 and 7 comprises some 50,000 points and it was surveyed in ten
working days with two total stations (Leica TCR407 and TCR805).

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Modelling strategies
Two strategies are employed in making 3D surface models of architectural features from the total
station data:
1. In situ architecture is principally modelled by creating digital elevation models (DEMs), or
triangulated irregular networks (TINs), in ArcGIS 9 (Fig. 8): the largest benefit is that the generation
of surface models of both architectural and current terrain features is automatic, and the algorithm
uses both line and point data in building up the models. The DEMs can directly be used to give the
AutoCAD building reconstructions their archaeological and current surface context.
2. The smaller architectural fragments are modelled in 3D using AutoCAD (Fig. 9). The surfaces are
constructed as polygon meshes based on the lines recorded with a total station, and the meshes
are created with AutoCAD's edgesurf command: in the central section of Fig. 9 one irregular
polygon mesh with the size of 12 × 24 rectangles is highlighted in darker colour than the rest. The
rendered solid fragments are used in the architectural models to display what is the relationship
between the preserved small fragments and the extrapolated reconstructions. The models are also
used to produce the publication plans and elevations of the fragments.
Fig. 9 – On the left wireframe of a column drum fragment as recorded, in the middle with surfaces as polygon meshes and on
the right the fragment with rendered surfaces (J. Pakkanen).
In the new excavation areas several architectural features have been discovered: detailed recording of
the walls and their archaeological contexts makes it possible to present DEMs of the various stages of
excavations. Fig. 10 illustrates the situation of one large trench at the end of the 2007 season (for a
report on the excavations, see PENTTINEN et al. forthcoming). The points and lines in the model
show where the nearly 20,000 total station measurements of this particular area were taken.
Vertical photography is used in the documentation of various phases of the excavations. A number of
reference points visible in the photos are marked on the ground and their positions are measured with
a total station. The images are processed using GIS where they are rectified and then placed in the
correct position in the employed coordinate system. The use of vertical photographs can greatly
reduce the loss of excavation data. It is also possibly to add further details to the 3D models by
draping actual photographs over the DEMs, as is illustrated by the model of the second large new
area opened during the excavation season of 2007 (Fig. 11).

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Fig. 10 – DEM of an excavation trench with architectural features: walls, column drums and recycled blocks (J. Pakkanen).
Fig. 11 – Three-dimensional computer model with a rectified photo draped over the archaeological features (E. Savini).

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Fig. 12 – Reconstruction of Building D superimposed on the actual remains (J. Pakkanen).
One further advantage of the architectural documentation and modelling strategies employed in the
research of the sanctuary of Poseidon at Kalaureia is in making the site more accessible to the wider
public: with no standing structures it is very difficult to understand the relationship between the
archaeological remains and how the built environment once looked like. The results of the new
research are being disseminated on the project website (www.kalaureia.org) and in brochures,
publications intended for the general public and new information panels at the site itself. These types
of media can make good use of the material produced for the research publications, and some new
material specifically generated for these purposes: Fig. 12 presents an integrated site photograph with
the architectural interpretation of Building D from south close to the entrance to the archaeological
site.
References
EITELJORG, H. II & LIMP, W. F. (2007) Archaeological Computing, Bryn Mawr, PA: Center for the Study of Architecture.
PENTTINEN, A., WELLS, B., HOOTON, A., KARIVIERI, A., MYLONA, D., PAKKANEN, P., SAVINI, E. &
THEODOROPOULOU, T. (forthcoming) ‘Report on the excavations in the years 2007 and 2008 southeast of the Temple to
Poseidon at Kalaureia’, Opuscula, vol. 2.
WELLS, B., PENTTINEN, A., & BILLOT, M.-F. (2003) ‘Investigations in the sanctuary of Poseidon on Kalaureia, 1997–2001’,
Opuscula Atheniensia, vol. 28, pp. 29–87.
WELLS, B., PENTTINEN, A., HJOHLMAN, J., SAVINI, E. & GÖRANSSON, K. (2005) ‘The Kalaureia Excavation Project: the
2003 season’, Opuscula Atheniensia, vol. 30, pp. 127–215.

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WELLS, B., PENTTINEN, A., HJOHLMAN, J., GÖRANSSON, K., KARIVIERI, A. & TRIFIRÒ, D.
(2006–2007) ‘The Kalaureia Excavation Project: the 2004 and 2005 seasons’, Opuscula
Atheniensia, vol. 31–32, pp. 31–129.
WELTER, G. (1941) Troizen und Kalaureia, Berlin: Verlag Gebr. Mann.
WIDE, S. & KJELLBERG, L. (1895) ‘Ausgrabungen auf Kalaureia’, Mittheilungen des Kaiserlich Deutschen Archaeologischen
Instituts. Athenische Abtheilung, vol. 20, 267–282.
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I am very grateful to Richard Anderson, Ann Brysbaert, David Johnson, Manolis Korres and Arto Penttinen for their comments
on the manuscript.