RESEARCH FOR THE POSSIBILITIES OF DIGITAL PHOTOGRAMMETRIC
METHODS FOR CLOSE RANGE STEREOSCOPIC PHOTOGRAPHS, APPLIED ON
THE RUINS OF TRANSEPT AND CHANCELOF THE CHURCH OF AULNE ABBEY
(THUIN, BELGIUM)
F. Benoit", D. Devriendt *’* ,J. Debie b , R. Goossens “
a Ghent University, Department of Geography, Krijgslaan 281 S8, 9000 Ghent, Belgium
(dennis.devriendt, rudi.goossens)@geonet.ugent.be
b Division du Patrimoine Ministère de la Région Wallonne de Belgique.
J.debie@mrw.wallonie.be
WGVII - Photography
KEY WORDS: Architecture, Cultural Heritage, Digital, Photogrammetry, Orthoimage, Softcopy, Close Range
ABSTRACT:
There has always been a need of documents, metric or non-metric, that give an overview of the state of buildings with a certain
historical, archaeological or cultural importance. This is certainly the case for the old church of the Aulne Abbey, Thuin, Belgium.
The goal of the project, described in this paper, was threefold. First of all there was a need for orthophotoplans of certain parts of the
church for archeological purposes. Second, and very close related to the first goal, was obtaining a three dimensional model of the
church ruins. This model is to be used in a later project, concerning the 3D visualisation of the site. The last, and most important
objective was to obtain a methodology for similar projects and sites in the future.The method described in this paper, covers the
whole workflow from fieldwork, over photogrammetric processing to orthophoto plans. The main problems that arose in the
develepment of this methodology was the presence of false parallaxes caused by doors and windows in the walls, and the angle by
which the photographs were taken. In some cases a solution was found by treating the photographs in a different way, accordingly to
the position of the camera at the moment of exposure. In a second project new photographs are taken in a perpendicular way for the
purpose of the planning of the restoration of the ruins.
1. SITE DESCRIPTION
The history of Aulne Abbey starts in the second half of the
seventh century. In that era monks raised the first buildings of
the Abbey near the river Samber. Very few of the buildings are
left today as they once were, and what rests are mainly ruins.
The abbey is located in the City of Thuin in Belgium.
*
Figure 1. View on from the south on the old Abbey church
There is a need of extended documentation on this ruins,
because the Belgian government is planning consolidation of
the site as it is now, rather than restoring the site in its original
state, starting with the transept and the chancel of the old abbey
church. One type of document that is required is an
orthophotoplan.
2. METHODOLOGY
2.1 Data acquisition and fieldwork
2.1.1 Artificial Ground Control Points:
For a number of reasons the choice was made to put artificial
marks on the wall, which serverd as ground control points
(GCP) for absolute orientation. Up to a height of seventeen
meters pieces of cardboard of six by six cm were collated to the
walls. For the higher parts of the walls, other ground control
points were selected, such as comer of stones, the top of an
arch.
The main reason to use artificial GCP is that they are easier to
locate, both on the terrain for the topographical survey, as on
the photographs.
2.1.2 Photography:
The photographs were taken with a Rollei 6008 metric camera,
with a 40 mm lense. A total of 65 stereopairs were made on 6
by 6 diapositives. Where possible the photographs were made
with the optical axis of the camera perependicular to the surface
of photographed the wall. In some cases an elevator was needed
because the opposite wall didn’t allow to stand far away from
the walls.
In some cases there was no other solution than to take the
photographs with a certain inclination angle, up to 45°.
Nevertheless, it was taken care of that within one stereopair the
optical axis of the camera were parallel to each other to avoid
large differences in inclination angles.lt was ensured that on
each stereopair a minimum of 6 GCP was well visible.
