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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012 
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia 
ORTHORECTIFICATION BY USING GPGPU METHOD 
H. Sahin*^ *, S. Kulur* 
“ General Command of Mapping, 06100 Dikimevi, Ankara, Turkey — hakan.sahin@hgk.msb.gov.tr 
° ITU, Civil Engineering Faculty, 80626 Maslak, Istanbul, Turkey - kulur@itu.edu.tr 
Commission IV, WG IV/3 
KEYWORDS: Processing, Programming, Orthorectification, Technology, Orthoimage. 
ABSTRACT: 
Thanks to the nature of the graphics processing, the newly released products offer highly parallel processing units with high-memory 
bandwidth and computational power of more than teraflops per second. The modern GPUs are not only powerful graphic engines but 
also they are high level parallel programmable processors with very fast computing capabilities and high-memory bandwidth speed 
compared to central processing units (CPU). Data-parallel computations can be shortly described as mapping data elements to 
parallel processing threads. The rapid development of GPUs programmability and capabilities attracted the attentions of researchers 
dealing with complex problems which need high level calculations. This interest has revealed the concepts of “General Purpose 
Computation on Graphics Processing Units (GPGPU)" and "stream processing". The graphic processors are powerful hardware 
which is really cheap and affordable. So the graphic processors became an alternative to computer processors. The graphic chips 
which were standard application hardware have been transformed into modern, powerful and programmable processors to meet the 
overall needs. Especially in recent years, the phenomenon of the usage of graphics processing units in general purpose computation 
has led the researchers and developers to this point. The biggest problem is that the graphics processing units use different 
programming models unlike current programming methods. Therefore, an efficient GPU programming requires re-coding of the 
current program algorithm by considering the limitations and the structure of the graphics hardware. Currently, multi-core 
processors can not be programmed by using traditional programming methods. Event procedure programming method can not be 
used for programming the multi-core processors. 
GPUs are especially effective in finding solution for repetition of the computing steps for many data elements when high accuracy is 
needed. Thus, it provides the computing process more quickly and accurately. Compared to the GPUs, CPUs which perform just one 
computing in a time according to the flow control are slower in performance. This structure can be evaluated for various applications 
of computer technology. 
In this study covers how general purpose parallel programming and computational power of the GPUs can be used in 
photogrammetric applications especially direct georeferencing. The direct georeferencing algorithm is coded by using GPGPU 
method and CUDA (Compute Unified Device Architecture) programming language. Results provided by this method were 
compared with the traditional CPU programming. In the other application the projective rectification is coded by using GPGPU 
method and CUDA programming language. Sample images of various sizes, as compared to the results of the program were 
evaluated. GPGPU method can be used especially in repetition of same computations on highly dense data, thus finding the solution 
quickly. 
1. INTRODUCTION Real time processing of imagery airborne data will be very 
: : : | important in the near future (Thomas et al. 2008). For rapid 
The graphic processing units (GPU) on the graphic cards evaluating data coming from unmanned air vehicles (UAV) in 
integral parts of computers are really developed today military applications, for supporting rescue and security forces, 
according to the last ten years. The development was the and also for obtaining surveys in disaster scenarios or mass 
increase of the GPUs performance and capabilities. The modern events an airborne real time image processing system is 
GPUs are not only became powerful graphic engines and also required. So the need is speed for processing the imagery data. 
they are high level parallel programmable processors with very 
fast computing capabilities and high memory bandwidth speed Thanks to the state of the art GPUs, there is now commodity 
comparing to central processing units (CPU). The rapid hardware, providing peak performances more than teraflops per 
development of GPUs programmability and capabilities second, and such tremendous computational resource certainly 
attracted the rescarchers dealing with complex problems who helps the goal of orthorectification in real time. 
need highly level calculation. This interest has revealed the 
Concepts of "General Purpose Computation on Graphics The announcements of immense computational speedups and 
Processing Units (GPGPU)" and "stream processing". fascinating developments in GPU hardware inspired to use 
general purpose parallel processing in image processing. In 
literature, there exists limited work about the orthorectification 
re iE a US 
T Corresponding author. This is useful to know for communication with the appropriate person in cases with more than one author. 
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