MEASURING ARCHAEOLOGICAL SITES USING EAGLE’S EYE
D. Skarlatos “•*, S. Theodoridou b , E. Karalis c , K. Tokmakidis d
^ National Technical University of Athens, 9 Iroon Polytexniou Str., 15780 Athens, Greece - dskarlat@survey.ntua.gr
b Polyline S.A., 54 G. Gennimata Str., 55134 Thessaloniki, Greece-sofia@polyline.gr
c GeoAnalysis S.A., 24 Plastira Str., 17121, Athens, Greece-ekaralis@geoanalysis.gr
d Aristotle University of Thessaloniki, Univ. Box 432, 54006 Thessaloniki, Greece-tokmakid@topo.auth.gr
KEY WORDS: Orthophotograph, bundle, platforms, photogrammetric recording and documentation, special methods of surveying
and mapping, precision, visualization.
ABSTRACT:
This paper reports on the experienced gained from three projects using a radio controlled model helicopter, as a semi-metric camera
platform. The modified helicopter carries a Rollei Metric camera and a small video camera as a viewfinder. The combination of low
height aerial photography and dynamic platform control, is very attractive to photogrammetrists. Problems as well as solutions,
possible improvements and statistics concerning commercial orthophotograph production in three sites will be discussed.
Speed, overall accuracy and appeal to the end users of the final products, is prosperous. Each case had different difficulties, with
Larisa’s case being the most difficult, due to its size and height differences. The ancient scene with vertical walls of 3 m height,
causing large occlusion with the 50mm lens, was the most challenging part. The final products were colour orthophotomaps of 1:50
scale. Other major problems which will be analysed are the aerial triangulation, concerning irregularity of aerial photographs, model
formation, epipolar imageiy generation and tilts, digital terrain modelling and model connection, contour generation and exclusion of
man made features, stone plots.
1. INTRODUCTION
The fast, accurate, cheap survey and visualization of
archaeological sites is a trivial demand, but far from fulfilment.
The necessity of monument surveying is clear. Restoration,
recording, reconstruction, or even study of an archaeological
site require accurate plots. Traditional method of string grids
does not meet the accuracy standards and simple survey of the
site can only provide a plan with a few accurate points
connected with vectors, without any further information. Both
methods have the disadvantage of extra people working within
the archaeological site for a prolonged period of time, which
increase the possibility of accidental destruction of important
findings.
Photogrammetry had a strong case in archaeology, but until
now end users were discourage by cost, time needed to develop
photographs and the fact that the final result was still a vector
plot. Evolution of computers and the passage from analytical
stereo plotters to digital ones, re-established photogrammetric
procedures and products as well as applications.
Under this new aspect, orthophotographs are a veiy attractive
photogrammetric product that can support documentation,
recording as well as restoration purposes (Baratin et al., 2000).
It is quite clear that photographic information with surveying
accuracy form an unbeaten combination. The only thing better
than this is a full 3d rendering of the site providing to the end
user the ability to precise measure 3d distances between points
himself (Dorffner et. al., 2000). These kinds of applications are
excellent provided the end user is computer literate and has
access to a powerful portable computer for in site use. Even if
he can overcome the aforementioned holdbacks he will still not
have in hand a paper copy for overview and communication
purposes with workers.
From this aspect orthophotographs are still the best possible
solution. What is still a disadvantage in comparison with ground
survey is processing time and cost.
Use of low altitude platforms for photography have been
reported in many cases (Miyatsuka, 1996, Theodoridou, et. al.
2000, Zischinsky et. al., 2000, Karras et. al. 1999, Ioannidis et.
al., 2000). Kites, balloons, cranes, helicopters, radio controlled
model helicopters, rope-way, fish rods and well buckets are
only some of the ingenious methods photogrammetrists are
using for low altitude photography.
In most of these cases, the ideal layout of the photographs is not
attained. This is reported in the case of the radio controlled
model helicopter (Tokmakidis et. al., 2002) and in the case of
the balloon (Karras et. al., 1999), and generally in any case
where the photographer cannot fully control the position (kites,
balloons) or he is not physically behind the camera (rope-way,
fish rods, well buckets). Although the radio-controlled
helicopter with a radio link for transmission of the imaged
object in the ground does not seems to suffer from the
aforementioned problems, this is not the case. Even highly
skilled operators cannot fully control the movement of the
model helicopter due to random wind blows and the inherent
manoeuvrability of the helicopter as a conceptual design.
Therefore the scale is not equal between photographs and
overlaps are far from the ideal (fig. 1). Model helicopter though
can easily capture an excessive number of photographs and
therefore allow for selection among them. Use of a full-scale
helicopter with a large format camera (13x18 cm) and the
operator on board as reported by Ioannidis et. al. (2000) is the
case which simulates the most aerial photography. On the other
hand there are some limitations such as:
• the necessity of a large format terrestrial camera in
order to keep the number of photographs as low as
possible,
• the necessary approval of the flight plan under the
proper authorities, especially for such low altitude
flights,
• the limited time in conjunction with the cost,
• availability and
• outsourcing.
