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«VIII CIPA
and Int.
sing, ISSN:
6.
K. 1999.
ligital close
tional Sym-
Photogram-
Vol. XXXII
PERFORMANCE EVALUATION
OF MULTIPLE SCALE AUTOMATIC AERIAL TRIANGULATION
A. Pothou *, Ch. Stamatiou, Dr. A. Georgopoulos
Lab. of Photogrammetry, School of Rural & Surveying Eng., National Technical University of Athens
apothou(@central.ntua.gr
Commission III, WG III/8
KEY WORDS: Automation, Correlation, Matching, Aerial Triangulation, Orientation
ABSTRACT:
Automatic Aerial Triangulation (AAT) is an increasingly interesting research topic. Most experiments have been carried out with a
view to testing accuracy and reliability of matching methods and it is thought that efficiency is directly related to successful
automation and increased accuracy. In the project presented here, we experimented with different scales and their combinations. The
project, the results and experiences of Automatic Digital Aerial Triangulation using images of different scales of the National
Technical University of Athens (N.T.U.A) campus are described. The entire area of the campus is covered by 1:3500, 1:6000 and
1:8000 image scales taken on the same day. The detailed aims of the project were to investigate, the geometric stability of the
blocks, the accuracy of the tie points and the derived orientation parameters. The program ISAT (ImageStation Auto Triangulation)
of Z/I Imaging was employed in this project, in order to adjust various block combinations. Firstly, both a manual and an AAT
solution for the 1:3500 block were performed. The computational time was about 3 minutes per image and the o, value was 0.30-
0.35 pixel. Secondly, AAT was applied to scales 1:6000 and 1:8000 and it was observed that for the 1:8000 images a less accurate
solution was obtained. Moreover, the combination of 1:3500 and 1:8000 image scales failed to provide a solution probably because
the software splits the block in two parts due to different resolutions. The combination of 1:6000 and 1:8000 image scales gave a
solution with impressive results. However, user intervention was necessary. Finally, a comparison of the above results with those
derived from an analytical solution of the same area and using the same images has been carried out.
Several researchers have reported attempts to automate Aerial
Triangulation, e.g., Tsingas (1991), Agouris (1992), Ackermann
& Tsingas (1994), Schenk (1995) and Toth & Krupnik (1996).
Several Automatic Aerial Triangulation packages have been
Automatic Aerial Triangulation (AAT) has been an increasingly developed over the recent years with different capabilities
interesting topic of research and development in digital (Büyüksalih & Zhang 2003). EuroSDR — formerly OEEPE —
photogrammetry. For a number of years, Aerial triangulation ^ devoted recently a common test to assess their performance.
has been a complex operation which includes planning the
photo flight, establishing ground control points, taking and
developing aerial photographs based on preset specifications,
performing interior orientation, measuring and transferring all
tie, check, and control points appearing on all photographs, and
performing a least squares block adjustment. This process
ultimately provides the exterior orientation parameters for all
photographs and the three-dimensional coordinates for all
measured object points.
1. INTRODUCTION
1.1 Automatic Aerial Triangulation
Recent progress in digital photogrammetry has brought to light
new possibilities. The impetus for this evolution has been the
advancement of computer technologies and image processing
: Figure 1: Automatic Aerial Triangulation
techniques. While the photogrammetric principles have not
changed, the imlementation tools have. An important 1.2 Motivation
advancement in digital photogrammetry involves automatic
aerial triangulation using image matching techniques to The aim of this project was to investigate the geometrical
automate point transfer and point mensuration phases, which stability of the block, the accuracy of the tie points and the
Were not available within the analytical stereoplotter derived orientation parameters using Automatic Aerial
environment. Several correlation techniques and computer Triangulation algorithms. It was decided to use a variety of
programs for digital aerial triangulation have been developed, image scales of the same area in multiple combinations, in order
based on the automatic selection and transfer of tie points using to derive substantial conclusions, spot eventually essential
Multiple image feature based and/or least squares matching. matching problems and present the results of these adjustments.
+ : ;
Corresponding author.
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