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CAD-SUPPORTED DETERMINATION
OF SENSOR ATTITUDE
IN TERRESTRIAL PHOTOGRAMMETRIC APPLICATIONS
A. D. Styliadis, P. Patias, J. Paraschakis
Dept. of Cadastre, Photogrammetry and Cartography
The Aristotle Univ. of Thessaloniki
Univ. Box 473 GR
540 06 Thessaloniki - Greece.
Commission V, Working Group 4
KEY WORDS: CAD, Modeling, Digital, Graphics, Photography, Camera Sensor Orientation, Computer Programming,
Archaeology Architecture Terrestrial.
ABSTRACT
The purpose of this work is to derive an easy-to-use interactive method, using simple CAD software, for the determination of good
initial values for camera positioning (Xo, Yo, Zo) and orientation (o, @, K rotations). It is actually a control-point-free method
intended for terrestrial photogrammetric applications, mainly in Architecture and Archaeology, dealing with facades.
Nowadays CAD vendors and current software provide the possibilities of entering raster images as well as easy manipulation of 3-D
vector graphics. Furthermore in CAD environments, friendly user interfaces using pop-up windows and dialog boxes give the user the
ability to view photographs and 3-D design files (e.g. a 3-D file for a facade) - in top, front, isometric and side views - at the same
time. The proposed system profits from these advances taking ideas and utilities in an attempt to solve a classical photogrammetric
problem, such as the determination of sensor attitude without control points, using CAD tools and programming techniques. In
terrestrial photogrammetry the calculation of approximated values for exterior orientation parameters is a difficult and time
consuming task.
The system is to some degree automatic, since it analytically computes discrepancy vectors and examines possible soluions to
minimise a penalty function. These different solutions are animated on the screen and the procedure is simply stopped by the user
when he feels the solution was achieved. When the solution deviates user interaction is possible. As a supplement to automatic
procedure a manual approach is provided for micro-corrections and enhancements. This manual approach is based on mouse
movements and appropriate push-button selections according to a predefined step.
have been gathered in an easy-to-use dialog box [Fig. 2]
offering a friendly graphical user interface (Young K., 1991).
The whole operational procedure is based on two facade's
Unlike the aerial case, where the sensor rotations are normally ^ models attempting to match each other on screen (CAD
small, in terrestrial applications, due to the complexity of the environment): The red TARGET model is built according to
cases, the rotations can range to any possible values. This provided image co-ordinates, and the generic CAD model is
creates a major problem in defining good initial values for the built according to any available distance measurements on the
0, 9, k angles to be entered to the subsequent photogrammetric ~~ facade. This matching is achieved after a continuous stepwise
adjustment. CAD camera's positioning and orientation. This CAD camera is
The problem is even worse in Architectural and Archaeological actualy a virtual camera provided by the CAD platform and
applications, where normally the use of low-end equipment is controlled by MDL-software in order to achieve good
desirable or simply used. Under these circumstances the number approximated values for exterior orientation giving minimum
of control points is relaxed, the cameras are of many types (from overall discrepancies for these two models.
amateurs to camcorders), surveying instruments may not be
used, and generally control information is reduced to simple
distance measurements for scale determination. Thus œ, 9, K 2. THE CAMERA-VIEW PROJECTION SYSTEM
rotations are rarely recorded and the determination of their
initial values becomes an empirical, time-consuming and often To work successfully in 3-D CAD environments there is a
very difficult job, many times performed by people (like necessity to view the models from any direction. In these
architects and archaeologists) with little photogrammetry environments a very good practice is: in order to change the
experience. direction, from which a CAD model is looked, the design cube
The developed system is based on Bentley’s MicroStation V5 offered by the environment is rotated to the required orientation
PC CAD environment, enhanced by dialog boxes and hook instead of the model itself. The result is visually the same. So,
functions implemented in an even-driven manner using the instead of the model the ‘world’ of the model is rotated. This
MDL programming language. The main MDL enhancements ‘world’ is CAD environment's design cube and virtual camera
(Wilkinson D., 1991).
1. INTRODUCTION
451
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
