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DIGITAL ORTHOPHOTO-SYSTEM FOR ARCHITECTURE REPRESENTATION 
Rainer Pallaske, Werner Marten, Landolf Mauelshagen 
Deutsches Bergbau-Museum (DBM) der DMT-Gesselschaft für Lehre und Bildung mbH, 
am Berbaumuseum 28, D-4630 Bochum 1, F. R. Germany 
ABSTRACT: 
For the documentation of facade structures a special solution has been developed for the production of 
orthophotos by different nonparametric rectification terms (projective transformation, bivariable polynoms 
n. order, multi-quadratic interpolation). A facade is divided in different planes and sub-planes, which can 
be projected independently and with freely selected transformation functions. Depending on the image 
quality of the surfaces different resampling functions can be chosen. The treatment can be done 
interactively within an image pyramid on higher levels by visual control. Control points and plane limits are 
predetermined by an analytical plotter. 
KEY WORDS: Architectural, Digital Systems, Orthophoto, System Design, Workstation. 
1. INTRODUCTION 
1.1. Documentation of Buildings 
Terrestrial photogrammetrictechniques have animportant 
rank for the documentation of buildings. The aim is an 
inventory of important objects of building history and to 
produce plans for planning and restauration works. The 
demand is the object restitution at a sufficient degree of 
details under cost-effectiveness. The document 
representation utilizes line drawings or controlled photo 
mosaics. The line drawing emphasize the object geometry 
interpreting the architecture historical and constructive 
features up to a desirable degree of abstraction. The 
actual inventory of a fagade can be shown in more detail 
and without interpretation by photo mosaics, as well as 
the documentation of decay. In certain cases a 
combination of both, line drawing and photo mosaics, is 
preferable as it gives a better perception of a building. 
1.2. Techniques of Documentation 
Inthe past controlled photo mosaics have been produced 
by rectification. The transformation was appliedto images 
or to parts of images of almost plane façades. This 
method was followed by the differential rectification, the 
_ orthophoto technique. But even this procedure has got 
its limitations, as surface structures with continual shape 
are presupposed (Seeger, 1979). Strong discontinuous 
shapes on façades are difficult to manage. Suitable 
transformations are required, which fit to the object and 
the task. Façades should be subdivided into delimited 
planes and other surfaces. The respective parts can be 
handled according their attributes by suitable 
transformations. 
1.3. Rule of Digital Rectification 
This demandfor various transformations can be realized 
onscanned images by digital processing. The production 
of digital orthophotos in the field of architecture 
photogrammetry has been shown by Bähr 1980 and 
Schweinfurth 1985. Today low-cost workstations and 
scanners allow economic solutions of digital 
transformation (Bähr and Wiesel, 1991). Digital methods 
make it possible to combine any given transformation, to 
integrate differentimage sources andto use the extraction 
of edges (Báhr, 1980). The following procedure shows a 
digital system for practical tasks of building documentation 
using partialimage transformation up to digital rectification. 
A universal and pragmatic approach should be in a 
position to handle any control information. The future 
directs to the field of stereo-image matching. 
2. CONCEPTION OF RECTIFICATION 
2.1. Choi f Transformation Functions 
The choice of suitable transformation functions shall be 
variable for partial planes and depend on the plane form 
and structure, direction of camera axis, distribution and 
position of control points, accuracy demands. 
The digital image processing consists of a plane 
transformation and a resampling of the pixel structure. It 
is favourable to choose the inverse transformation (indirect 
method) and to compute the resampling from the original 
image matrix. Different pixelinterpolations are at disposal 
(nearest neighbour, bilinear and bicubic spline 
interpolation). The choice has to result individually from 
theimage contents ofthe respective partial plane, because