Gamal Seedahmed 
  
MODEL-BASED AUTONOMOUS INTERIOR ORIENTATION 
Gamal Seedahmed, Toni Schenk 
Department of Civil and Environment Engineering and Geodetic Science 
The Ohio State University 
Columbus OH 43210-1275 USA 
{seedahmed.1,schenk.2} @osu.edu 
TECHNICAL COMMISSION III 
KEY WORDS: Autonomous Interior Orientation, Hough Transform, Least Squares Adjustment. 
ABSTRACT 
The model-based approach to autonomous interior orientation is an entirely novel approach. It is driven 
by the simple structural description that one can build for a fiducial mark. In this research we have 
focused on recognizing and measuring the fiducial marks automatically. This is motivated by the desire 
to establish an automation chain in digital photogrammetry, starting with the interior orientation. We 
benefit from a simple fact that fiducial marks are artificial objects projected onto the film during 
exposure time. Most every fiducial has a simple, regular shape. This invites us to represent the fiducial 
marks as a structural description and to detect the structural elements in the image. The CAD design of 
the fiducial mark and the optical parameters of the projection lens are used to build a geometric model 
for the fiducial mark. Edge detection is performed to generate image primitives. The Hough Transform 
is executed over the edge image for identification and approximate localization. Least Squares 
Adjustment is used for precise localization and the affine transformation is used to compute the 
transformation parameters. The results of the Hough Transform, represented in the accumulator array, 
are analyzed via quadratic conic section fitting. The analysis of the fitted conic section renders valuable 
information regarding the surface complexity in terms of noise and the surrounding structures to the 
fiducial mark. A fast version of the Hough Transform, for the peak detection, is implemented via 
histogram peak detection. The developed technique is capable to handle noisy and partially detected or 
missing information of the fiducial mark. The collected evidence in terms of hypothesis generation, 
verification, and validation allows us to define a percept sequence to reason about the recognition of 
the fiducial mark. 
1 INTRODUCTION 
1.1 Photogrammetric Tasks 
The main task of photogrammetry-analog and digital alike-is to reconstruct the object space from 
images. This reconstruction can be considered as the inverse process of image formation. The latter 
proceeds from the scene to the image while reconstruction begins with images and ends with a suitable 
description and representation of the scene. One task of reconstruction deals with determining positions 
of features in the object space from known quantities in the image space. Before computing positions in 
the object space, two major tasks must be solved, however. For one we need to determine the exterior 
orientation of the camera- its position and attitude referenced in the object space. The other prerequisite 
is the interior orientation, the subject of this study. 
Image orientation is a prerequisite for any task involving the computation of three-dimensional 
coordinates. Image orientation refers to the determination of parameters describing specific 
photogrammetric models for mapping geometric primitives such as points, lines, and areas from one 
coordinate system to another. A coordinate system relevant to photogrammetry is the object, the model, 
the image, and the pixel or stage coordinate system (Heipke, 1997). Due to their importance, image 
orientation has always been a focus of attention in the photogrammetric community. The interior 
orientation is the starting point in image orientation. 
1.2 Anatomy of a Fiducial Mark 
The fiducial marks are located on the upper surface of the inner cone of an aerial camera. They are 
located either at the four corners of the format opening and/or in the center of the four sides. Fiducial 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 
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