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MONOTORING THE WEATHERING OF STONES: SETUP AND FIRST RESULTS
Michael Kempa
Institute of Photogrammetry and Cartography, TH Darmstadt, FRG
ISPRS Congress, Comm. V, Washington 1992
ABSTRACT
A lot of architectural monuments of the Middle Ages are threatened
by continuous pollution,
especially facades by weathering of
stones. Initialized by the Institute for Preservation of Stones in
Wiesbaden (FRG) photogrammetric measurements were made to get nu-
merical information about this process at the romanic monastery
Limburg - partly destroyed by a fire since the 16
century. Parts
of stones on a cross column were selected and a comparison of two
surfaces with a time delay of one year has to be photogrammeti-
cally generated. Because of the high accuracy
demanded for this
task (about 0.1-0.3mm) two terrestrial survey cameras (Wild P32)
were modified and calibrated for this close-range application
(image scale about
1:8). The procedure and
first results
(numerically and graphics) will be presented.
KEYWORDS
Architectural, Calibration, Close-Range, DEM
INTRODUCTION
A lot of architectural monuments of
the middle ages are threatened by conti-
nuous pollution. This concerns entire fa-
cades as well as small details of cul-
tural-historical importance. Curators of
monuments are confronted since a longer
time with this problem und cooperate with
experts of scientific disciplines
(chemical engineers, mineralogists etc.).
Thus chemical and environmental influen-
ces and causes are searched but in this
way no statement is possible about the
quantity of the weathering process during
a fixed period. Hence, for curators of
monuments this is a first indicator if
precautional measures against the weathe-
ring of stones are necessary or not.
PARTICIPANTS AND HISTORY OF THE OBJECT
Two years ago the Institute for Pre-
servation of Stones (IfS) was founded.
Its main tasks are chemical and mineralo-
gical research work. In addition a pilot
project initiated by Dr. Kraus with the
Institute of Photogrammetry (TH Darm-
stadt) was defined: surfaces of natural
stones are surveyed photogrammetically to
get information about, the quantity of
loss caused by weathering. As test object
parts of stones were chosen on a cross
column of the monastery Limburg a. d.
Haardt (close to Bad Dürkheim / Pfalz, s.
fig. 1). The time delay between two sur-
veyings is a little bit more than one
year.
The former monastery Limburg is a
foundation of the emperor Konrad II. and
was build up between 1025-1042. It was
destroyed for the most part by a, great
fire in the beginning of the 16th cen-
tury. Afterwards the church was only re-
built incompletely /DEHIO 1984/. Since
that the nave without roof is exposed to
the weather (s. fig. 2). Since 1969 re-
storation is carried out but refer only
to the brickwork. Almost all of the ori-
ginal stone surfaces, hewed,in the stone-
mason-technique of the 11 century and
very often similar to a herringbone pat-
tern, are destroyed and completely washed
out /Dólling 1979/.
Surfaces of natural stones have al-
ready been surveyed with photogrammetric
measuring techniques. There, either the
classification of different zones of va-
rying level of damage or the determina-
tion of the loss of surface were carried
out, s. /Heckes et al. 1988, Grassegger,
Eckstein 1990, Mauelshagen , Stracken-
brock 1990, Strackenbrock et al. 1990/.
The results and experiences have shown
that the quantitiy of the weathering pro-
cess can be evaluated by close-range pho-
togrammetry.
In the following the own approach for
surveying surfaces of natural stones is
presented: equipment, measuring design
and first results of one epoche. The com-
parison between two epoches and quanti-
ties concernig the waethering process are
not yet finished. However, the results
will be presented just intime at the
ISPRS congress in Washington.
