The International Archives of the Photogrammetry. Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
(a) Spot image before floodings (b) Spot image after floodings (c) Change detection 
Figure 6: Change detection example on two SPOT5 images from before and during floodings in the north of England with a mean 
difference change detector. 
Libraries 
Functionalities 
ITK 
Architecture, Segmentation 
Registration 
libsvm 
Support Vector Machines 
boost 
Graph representation 
ossim 
Sensor models, DEM handling 
6S 
Radiometric corrections 
Gdal 
Image formats 
dxflib 
DXF format 
OpenJPEG 
JPEG 2000 format 
Table 1: Open source libraries and functionalities used in OTB 
requirements (open source). Access to these libraries is then in 
tegrated in the framework of OTB. 
4.1 Image processing 
The core of the OTB system is coming from ITK which has 
proven its efficiency for medical image processing. Most of the 
algorithm for segmentation and registration have been well tested 
in this context. For the Support Vector Machine (SVM), OTB in 
cludes the libsvm library. The graph representation is done using 
Boost library. 
4.2 Specific remote sensing processing 
Sensor models, map projections and DEM handling capabilities 
are provided by ossim. The sensor models are integrated as a 
special type of ITK transforms which enable an elegant struc 
ture for the orthorectifications. Radiometric correction capabil 
ities are provided by 6S. 6S is originaly a fortran code that has 
been automatically translated in C to enable integration into OTB. 
4.3 Image format 
Most image formats are read through GDAL, enabling OTB to 
read and write numerous image format. DXF files are handled by 
dxflib library. For the case of JPEG 2000, as options required by 
satellite images were not available in JPEG 2000 implementation 
with compatible licence, CNES participated to the development 
of OpenJPEG to add these capabilities. 
4.4 Great results with minor efforts 
As we can see, many functionalities are available, well-tested in 
the open-source community, and can be integrated to an existing 
project at marginal cost. When only few options are missing, it is 
usually quite easy to contribute to the project to add these options. 
5 VALIDATION ELEMENTS 
OTB is a complex system and needs to be validated both at a 
computing engineering level and at functionality level. Automa 
tion is the key factor for an efficient validation. Every class is 
coming with some tests to check the non regression and the va 
lidity of the results. All these tests are executed every night on 15 
different platforms with different compilation options. Impact of 
modifications on one class is clearly visible on the whole library 
for the different compilers and compilation options. 
A more difficult part, but critical for the OTB user is the valida 
tion of the proposed functions from an application point of view. 
Basically, this is not because a program return a good looking 
result that the program is correct. For this validation, in-depth 
knowledge of the functionalities is compulsory. That is why it is 
particularly important to start with existing and validated devel 
opments or to rely on experts for each domain. 
6 COMPUTING ASPECTS 
6.1 Multiplatform 
The library is multiplatform and works under different operating 
systems (Linux, Unix, Windows, or MacOS) and different archi 
tectures (32 or 64 bits) to get rid of hardware constraints. The 
multiplatform aspect is also very important because it imposes 
to follow strict design and coding rules thus leading to a robust 
system less sensitive to particular platform specificities. 
6.2 Large data processing 
One frequent problem when going from the research algorithm to 
the real application is the difference in the data size. A satellite