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ORTHORECTIFICATION OF SPOT IMAGES WITH THE SAME-PASS CONSTRAINTS 
M. Erdogan, O. Eker, A. Yilmaz, O. Aksu 
General Command of Mapping, Photogrammetry Department, 06100 Dikimevi Ankara, Turkey 
(merdogan, oeker, ayilmaz, oaksu)@hgk.mil.tr 
Commission IV, WG IV/7 
KEY WORDS: Orthorectification, Accuracy, Imagery, Photogrammetry, Remote Sensing 
ABSTRACT: 
SPOT images are one of the most widely used satellite images in middle scale mapping applications for its stereo capability, wide 
coverage area and well-known satellite model which is supported nearly in all photogrammetric software. Stereoscopic imaging 
capability of SPOT allows generating digital elevation models (DEM) from a pair of overlapping images. DEMs based on satellite 
images are essential for many applications when you need up-to-date and cost-effective information about terrain relief. 
Topographic mapping contouring and orthoimage generation are the two widely used application areas. 
The accuracy of orthoimages is a function of many variables, one of which is the accuracy of the ground control information used in 
a simultaneous adjustment and updating the satellite model parameters. Both the number and distribution of the ground control 
points are of great importance. Some techniques can reduce the needed number of ground control points in the modelling of SPOT 
images. This is important when the control points are acquired by expensive differential GPS measurements. 
GCPs are used to calculate the position and orientation (i.e. roll, tilt, and yaw) of the imaging system at the moment of image 
taken. This calculation is accomplished using standard photogrammetric algorithms, such as a space resection or bundle 
adjustment. In these algorithms, same constraints may reduce the number of the ground control point needed. For SPOT system, 
when the images are taken in the same-pass, some additional constraints can be added to the adjustment process which will reduce 
the number of unknowns resulting reduction of the number of GCPs. By this way, the production cost and time will be also 
reduced. 
In this study, a block with two columns each of which consists of three SPOT frames from the same pass was used. Finally, the 
accuracies were investigated. 
1. INTRODUCTION In orthorectification, the distortions induced by the imaging 
platform, film and three-dimensional shape of the Earth are 
Remotely sensed images offer a unique perspective of the digitally removed from the space imagery. The final result is an 
Earth, its resources, and human impact upon it. In little more image that has a precise geometry of a map which is a very 
than a decade, remote sensing technology has proven itself as a popular product due to its diversity of use, particularly in its 
cost-effective source of valuable information for numerous use as base information for Geographic Information Systems 
applications including mapping, urban planning, environmental (GISs). Applications in many disciplines integrate the existing 
monitoring, agricultural management, oil exploration, market line data with digital images. One useful and very common 
development, real estate siting and many others. In many ways, integration is that of orthorectified images input directly into a 
the value of remotely sensed satellite images has become GIS. This is quite advantageous for providing a base for a new 
obvious. They provide an overhead look at the features on data set or for updating existing databases. Another remarkable 
Earth surface and help to understand relationships among these advantage of digital orthophotos is that they provide a more 
features. readily usable data source for a GIS when compared with 
conventional data sources. Because the information is not 
fillered through a cartographic interpretation, it remains 
unbiased. The relationships among land features such as 
buildings, transportation networks, etc. are presented in their 
natural form without being skewed by data conversions and 
interpretation. In addition, digital orthophotos are already in 
digital form and unlike hardcopy maps, they can be integrated 
directly into a GIS. Digital orthoimages serve as the backdrop 
with which older vector data can be updated or corrected. With 
the launch of new high-resolution satellites, an increasing 
number of orthoimages will be seen to be integrated into GISs. 
Up-to-date maps are the basic need in many applications. The 
need for up-to date information drives the use of satellite 
imagery in mapping technology. Classical methods need years 
to produce a map, which is not preferable for the rapidly 
changing world. Remote sensing has become a solution for that 
problem and new technologies were developed through the up- 
to-date map needs. One of these technologies, which is very 
rapid and easy to use for mapping purposes, is the digital 
orthoimage, a photographic image that has been orthorectified 
to meet the precision and accuracy standards of a map. 
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