THE CONSTRUCTION OF AN ANCIENT BAS-RELIEF REPLICA USING 
PHOTOGRAMMETRIC METHODS AND CNC TECHNIQUES 
E. STAMBOULOGLOU, Managing Director, Fotopo Ltd, Greece 
Commission V, Working Group 4 
KEY WORDS : Photogrammetry, Archaeology, Reconstruction, Close_Range, Three-dimensional 
ABSTRACT 
This paper describes a replica efficient production process of ancient sculpture with bas-relief, avoiding totally the contact with 
it. Analytical Close-Range methods combined with Computer Numerical Control (CNC) techniques make possible the 
construction of the replica. A strong point of the process is the possibility of endless replica production in the same scale or 
smaller scale. 
1. Introduction 
The construction of replica of ancient objects like 
sculptures and bas-relief is a routine process for the 
Archaeological Service, the Archaeological Schools and 
Museums. 
The conventional technique which is used to obtain such 
replica consists of two steps. During the first step the 
technician make a negative surface of the original object 
using a special rubber material. To obtain the desired 
results the original object must be placed in horizontal 
position to facilitate the application of the liquid rubber on 
top of it. Additional rubber material is also needed in 
difficult areas with hidden and negative concave surfaces. 
Soon after the rubber solidification, the technician can 
produce the desired positive replicas with the same 
negative rubber but not more than a few copies. The 
reason is that the rubber is damaged with every use. This is 
the second step. 
The described conventional process is applicable to 
object which can be moved to horizontal position and have 
a skin-surface which allows the contact of the rubber 
material. 
The Committee for the Conservation of the Monuments of 
the Athens ACROPOLIS, signed a contract with our 
company for a pilot project concerning the investigation of 
new methods and techniques for the production of replicas 
avoiding the contact of the damaged original object with 
any material, with an accuracy of 1 millimeter. 
The pilot project was designed and realised in Greece, by 
Greek scientists and technicians. 
The proposed original object was a 1,20m X 1,10m marble 
bas-relief plate from the Zoforos of Parthenon (0,15m 
maximum relief), the first from the Procession of 
Panathenea. The traces of air pollution, erosion and brutal 
human action transformed the invaluable monumental 
bas-relief to it'S present status. 
2. The Photogrammetric Process 
546 
Conventional Close Range Photogrammetric method was 
applied for the detail survey ofthe original object in order to 
avoid any contact with it. 
The object is situated in vertical position on a special stand 
inside the Acropolis Museum. Several (13) pre-marked 
self-adhesive control points were put to cover the object 
space. The set of 13 control points were determined using 
special techniques and combined measurements with 
digital theodolite and metal tape, with sub-millimeter 
accuracy. The maximum depth of the object relief is of 
15cm having some difficult small areas with negative 
(concave) surfaces. In order to cover those areas, two 
pairs of photos were taken with an UMK /10-1318 camera 
from a distance of approximately 2 meters. 
The Analytical Stereoplotter Digicart 40. was used for the 
restitution of the two stereoscopic pairs. An enormous 
number of 3D-break lines and 3D-points formed the 
restitution data for the detailed representation of the object 
and contributed to the formation of the object surface. The 
rms residuals (X,Y,Z) of absolute orientation for both 
couples were within 0,3 mm. 
The restitution file was transformed in DXF format in order 
to be used in Autocad R12. The graphical representation of 
the surface was made with 1mm contour lines, produced 
with QuickSurf/ SCHREIBER, a vertical application of 
Autocad R12. 
A detailed map with the 1 mm contour lines, in scale 1 : 1 
was plotted. With the use of QuickSurf a digital surface 
(binary file) was produced together with an output file in 
3d-mesh form. 
3. The CNC process 
The CNC machine works with data produced and 
organised by special S/W. The existing S/W are designed 
to cover the needs for the production and construction of 
objects with few surfaces described with simple 3d-planes 
and 3d-curves. 
Three different S/W were used for the process and the 
production of the required output for the CNC machine. All 
of them failed to process the surface data, not even a 
portion of it. ) 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
Fina 
reali 
Desi 
sma 
poss 
sma 
The 
3 di 
mac 
with 
Man 
opel 
proc 
form 
slice 
form 
Drav 
surf: 
ame 
The 
rect: 
Ever 
mac 
dian 
step 
sec 
Fina 
posi 
neg: 
surf 
neg: 
The 
(ma