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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
block adjustment can be started again, without repeating the 
automatic process (Sigle & Heuchel 2001). 
Having approximate exterior orientation parameters and image 
overlaps available, the AAT approach starts with a block 
formation based on feature based matching (FBM) and runs 
through overview levels to generate a primary point list. The 
match with the largest correlation coefficient yields the most 
likely homologue point. Feature based matching determines the 
correspondence between image features. Least squares 
matching requires accurate approximate values (Figure 4). It 
refers to the determination of the correspondence between 
image area based matching on the similarity of their gray 
values. The cross correlation and the least square matching are 
the appropriate methods. So that, after the FBM, the collinearity 
equations can be used as a convergence based on least square 
matching (LSM) and can work more accurately and improve the 
success rate of the matching. (Dórstel et al. 2001). 
  
  
  
   
  
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BE homologous image 
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preliminary matching in 
all combinations 
  
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Figure 4: Matching Scheme in the Kernel System 
The work by Tsingas represents the first research on fully 
automatic digital aerial triangulation (Ackermann & Tsingas 
1994). Instead of gray levels interest points are used as 
matching entities and the matching method is based on graphs 
(Jaakola & Sarjakoski 1996). 
In addition, ISAT generates considerably more conjugate points 
and point clusters in the areas of multiple overlap areas. Finally, 
the produced data are the orientation parameters for the images 
and the analysis of results. 
2. PERFORMED TESTS 
2.1 Preparation of projects 
For testing the AAT algorithm, several tests were performed 
with the data available. Firstly, a manual solution and an AAT 
solution were performed for the same block of the 1:3500 
images. Secondly, the comparison of two solutions for the 
1:3500 images, using different number of patches in each one, 
was carried out. Thirdly, AAT was applied separately to scales 
1:6000 and 1:8000. Moreover, the combinations of 1:3500 with 
1:8000 image scales and 1:6000 with 1:8000 were also tested. 
The most important project parameters were defined as follows: 
as coordinate system the Greek System EGSA87 was used, the 
average ground elevation was set at 300m, the standard 
deviation for the photo measurements 7um, the 6,,,, for interior 
orientation 10um, the o,,,, for the relative orientation 10pm and 
the Gmax For the absolute orientation 10um. 
The main tests performed include the following projects: 
I. Manual aerial triangulation with measurement of tie and 
control points in images of 1:3500 scale using ISDM. 
Autotriangulation adjustment of the 1:3500 scale images, 
using a 3x3 pattern of vonGruber point positions with ISAT 
3. Autotriangulation adjustment of the 1:3500 scale images, 
using a 5x5 pattern of vonGruber point positions with ISAT 
4. Autotriangulation adjustment of the 1:6000 scale images 
with ISAT 
5. Autotriangulation adjustment of the 1:8000 scale images 
with ISAT 
6. Autotriangulation adjustment of the combination of 1:6000 
and 1:8000 scales with ISAT 
7. Autotriangulation adjustment of the combination of 1:3500 
and 1:8000 scales with ISAT 
N 
For every project the appropriate data files were created and the 
various parameters were defined. They include, among others, 
camera, photo, model, control points, altitude information, such 
as flying height and average ground elevation, the desired linear 
and angular units, the type of imagery and camera parameters 
(such as name, lens distortion values, focal length, and principle 
point coordinates), the order of images and strips and the 
coordinate system for the control points. The essential number 
of overviews for every image is created with the Gaussian 
method of resampling - full set is recommended - so that the 
images may be better manipulated by the software (Z/I 
Imaging, 1999). 
2.2 Images of 1:3500 scale 
The 1:3500 scale images were ordered in two strips, with a 
mean absolute flying height of about 1000m. Initially, the 
interior orientation process for every individual photo, with the 
help of the corresponding module of Automatic Orientation, 
was performed. 
2.2.1 Triangulations with manual measurements of tie 
and control points: As already mentioned, an adjustment of 
manual measurements of the 1:3500 images was initially 
performed. Tie and control points were measured in every 
photo in which they were well defined. 
2.2.2. Autotriangulation (using a 3x3 pattern of vonGruber 
point positions): For this project approximate values of the 
exterior orientation parameters were provided, with an accuracy 
of 50m fof the projection centers, while the o, q angles were 
considered equal to zero and the k angle was calculated from 
the approximate values of the image centres. The initialization 
automatically creates nominal tie-points, in object coordinates, 
for later use in correlation. These nominal tie-points (in a 3x3 
vonGruber point pattern) will be used later by ISAT to generate 
. clusters of matched points. Default value for the size of every 
597 
patch window is 100x100 pixels. As an example of the 
matching method, tie points in multi-photo view are presented 
below. The user is obliged to control the success of the 
algorithm visually.