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Maurizio Barbarella , Renzo Carlucci 
PHOTOGRAMMETRIC STRUCTURED DATA ACQUISITION AND COMPRESSION AIMED TO STATIC 
ANALYSIS BY FINITE ELEMENTS METHODS - A TEST ON THE COLOSSEO 
, Margherita Fiani', Stefano Paradisi 
* Dip. Idraulica, Trasporti e Strade - Univ. di Roma "La Sapienza" - Italy 
* Dip. Architettura e Urbanistica - Univ. degli Studi dell'Aquila - Italy 
ISPRS Commission V 
ABSTRACT 
Of the current survey operations on the Colosseo, photogrammetry of the face 
is undoubtedly one of the most urgent preliminary stages in filling the gaps 
in basic documentation which have hitherto hindered the studies and analyses 
required for adequate protection of the monument. This note describes the 
results from a specific photogrammetric data acquisition procedure which takes 
account of the subsequent specific data processing operations. This procedure 
uses a plotting instrument and contemporaneous restructuring of the data into 
categories which are also topologically defined. The data are thinned to 
extract coordinates of characteristic points for definition of a correct basic 
geometry for input to structure evaluation programs using the method of finite 
elements. 
Key Words: Data Compression, Architectural Photogrammetry, Structural Analisys 
1. INTRODUCTION 
In general, the use of photogrammetry for 
surveying architectural structures may 
produce different results according to 
the quality and quantity of the elements 
plotted. 
This is due to dependence on subjective 
interpretation of the photographs 
(present even when 3D stereoscope vision 
is used), and is also related to the 
multiplicity of meanings given to the 
word "survey". 
In our case, we tackled the requirement 
stated by structure experts for automatic 
processing of often excessive 
photogrammetry data to create a model 
more suitable for finite element 
calculation. 
An attempt was also made to create a 
hierarchical structure for the data that 
would permit automatic generation of 
surfaces for computer graphics display. 
2, GENERAL APPROACH TO PHOTOGRAMMETRY 
The Colosseo survey (Birardi et Al., 
1987; Carlucci, 1989) was started in 1987 
by the "Topografia e Geodesia" section of 
the "Dipartimento di Idraulica, Trasporti 
e Strade" of the "La Sapienza" University 
of Rome. 
The photos covered the entire external 
face and were taken on 4x5 inches color 
Slides with 99.66 mm focal length and a 
mean scale of 1:300, suitable for 
restitution up to scale 1:50. 
The control points on the monument were 
determined by the vertexes of a general 
topographical grid and were situated one 
for every two columns for the first three 
levels, less closely for the attic. 
  
The r.m.s. obtained in compensation for 
each X and Y coordinate did not exceed 2 
mm. Heights were derived from the mean of 
all the zenithal measurements. 
The coordinates of the control points 
were, as stated, calculated in a 
reference system external to the monument 
(and linked to the national system). To 
make plotting of the sample model 
possible (the axes of the plotting 
instrument reference system do not 
correspond to those of the external 
reference system), a local (orthogonal 
cartesian) system of coordinates was 
devised effecting a rotary-translation in 
such a way as to have one axis parallel 
to the straight line —. joining . two 
successive control points on the external 
wall (and the origin at the first of 
them). A subsequent inverse  rotary- 
translation makes it possible to bring 
each point measured into the original 
general reference system. 
The pair of photograms was oriented 
absolutely on the control points referred 
to the aforesaid "local system", and the 
residuals for the three coordinates of 
each point resulting from calculation of 
the parameters of absolute orientation of 
the model were less than 2 mm. 
The application presented is limited to a 
portion of the external wall of the 
Colosseo, specifically the ground level 
arch with the Roman numeral XLII carved 
on the travertine. 
Plotting was effected using the pair 
formed by photograms 15a and 16a and 
performed with the Digicart40 analytic 
plotter from Galileo Siscam. 
Specific attention was given to the 3D 
aspect of the analytical numerical 
restitution so as to produce a truly 3D 
model (Figures 1 and 2).