1095 
USE Of LINE SEGMENTS IN HIGH RESOLUTION SATELLITE IMAGE 
REGISTRATION 
J.Heikkinen, A.Laiho-Heikkinen, H.Haggren 
Helsinki University of Technology, Department of Surveying Sciences, 
Group of Photogrammetry and Remote Sensing 
FINLAND 
- Jussi.Heikkinen@tkk.fi 
Anita.Laiho - Heikkinen@tkk.fi 
Henrik. Haggren@tkk. fi 
Commission VII, WG VII/6 
KEY WORDS: Remote Sensing, Adjustment, Registration, Data Fusion, Georeferencing, High Resolution, QuickBird 
ABSTRACT: 
In recent years the research activity in image registration has grown at the same pace as the high resolution satellite images have 
found their way to end users. Much of this research activity has concentrated on methods improving the accuracy of georeferencing 
provided as RPC values. In this study the image registration via projective transformation based on straight line segments is 
investigated. The transformation parameters are solved based on real data extracted from topographic database and measurements 
done on QuickBird image. Same data is processed also with point wise method and accuracy numbers in selected check points are 
calculated. The RMS values computed in same check points prove that with the line based method the equivalent accuracy can be 
achieved as with the point wise method computed with minimum number of observations. In a smaller sub image the accuracy of 
transformation with line segments could be verified to be in size of a pixel. 
1. INTRODUCTION 
Georeferencing is an essential part of the process when 
combining satellite images acquired in different epochs or with 
different sensors. If data fusion is needed for image 
interpretation, classification, or change detection, precision of 
image registration has to fulfil task specific requirements. In 
point-wise method georeferencing can easily be accomplished 
within precision of one pixel. However, this precision usually 
requires manual work in selecting good points and satisfying 
proper point distribution. This is tolerable if the number of 
images to process is reasonable, but in case the data processing 
is regular and rather frequent, some automation for image 
registration is needed. Taking care of point distribution is a 
fairly straight forward task, but to recognize correspondences 
automatically is a demanding task. At the moment, most of the 
implementations of automatic image registration do rely on 
point-wise observations and area-based matching strategies. In 
a simple case they do succeed reasonably well, but in a more 
complex case they tend to suffer from some drawbacks. Most 
problematic in determination of correspondences is to deal with 
differences of varying radiances of an object point in case of 
images from different epochs. Also, when using point-wise 
methods and area-based matching strategies, discrepancies of 
occlusion patterns and casting shadows due to varying sensor 
orientations and time of acquisition affect results. By using 
feature-based matching approach there are better chances to 
detect these pitfalls automatically. 
Feature-based matching algorithms exploit the power of 
interest-operators in order to extract large number of feature- 
point observations on cost of accuracy of an individual 
measurement. However, there is an option to extract feature 
lines instead of feature-points. The fact that straight lines 
project as straight line segments on images speaks up for using 
these straight line segments in image registration. While 
searching correspondences multiple matching clues connected 
with line-features do enhance and encourage to exploit 
automation in image registration. 
Full strength of line-based methods can be exploited if there are 
line segments on images which are substantially long compared 
to image dimensions. Unfortunately, this requirement is rarely 
fully met with satellite images. This drawback has been avoided 
in investigation of Barakat (Barakat et.all.,2004) by measuring 
few fairly good control points on images and constructing 
Active lines between those measured points. The selected points 
were considerable long distance apart from each other 
constructing a solid base for line-based projective 
transformation. This way it was possible to solve transformation 
with fewer points than what would have been required to 
achieve the same accuracy in estimation with equations based 
only on point observations. 
However, line segments to be detected on high resolution 
satellite images are long enough to be used alone in solving the 
image registration. Earlier, line-based methods have 
successfully been used with aerial images for map revision 
processes in order to solve sensor orientation and reconstruct of 
object features. The stability of line-features have been found 
robust and feasible in such tasks (Mikhail&Mulawa,1988), 
(Mulawa, 1989),(Heikkinen, 1994), (Mikhail&Weerawong, 1994), 
(Habib, 1999). 
In this paper it will be shown that image registration can be 
accomplished within precision of few pixels using purely line