A brief tour of OTB-Applications


OTB Applications was perhaps the older package of the Orfeo Toolbox suite after the OTB package itself. Since the Orfeo Toolbox is a library providing remote sensing functionalities, the only applications that were distributed at the beginning were the examples from the Software Guide and the tests. These applications are very useful for the developer because their code is very short and only demonstrates one functionality at a time. In many cases, a real application would require :

  • combining together two or more functions from the Orfeo Toolbox
  • providing a nice high level interface to handle : parameters, input data, output data and communication with the user

The OTB Applications package was originally designed to provide applications performing simple remote sensing tasks, more complex than simple examples from the Software Guide, and with a more user-friendly interface (either graphical or command-line), to demonstrate the use of the Orfeo Toolbox functions. The most popular applications are maybe the otbImageViewerManager , which allows to open a collection of images and navigate in them, and the otbSupervisedClassificationApplication , which allowed to delineate training regions of interest on the image and classify the image with a SVM classifier trained with these regions (this application is no longer maintained since the same functionnality is available through the corresponding Monteverdi module). During the first 3 years of the Orfeo Toolbox development, many more applications have been added to this package, to perform various tasks. Most of them came with a graphical user interface, apart from some small utilities that are command-line.

The development and release of the Monteverdi software (see chapter [chap:Monteverdi] at the end of year 2009 changed a lot of things for the OTB Applications package: most of non-developer users were looking for quite a long time for an application providing Orfeo Toolbox functionalities under a unified graphical interface. Many applications from the OTB Applications package were integrated to Monteverdi as modules, and the OTB Applications package lost a lot of its usefulness. No more applications were added to the package and it was barely maintained, as new graphical tools were directly embedded within Monteverdi .

Then, some people started to regain interest in the OTB Applications package. Monteverdi is a great tool to perform numerous remote sensing and image processing task in a minute, but it is not well adapted to heavier (and longer) processing, scripting and batch processing. Therefore, in 2010 the OTB Applications package has been revamped: old applications have been moved to a legacy folder for backward compatibility, and the development team started to populate the package with compact command-line tools to perform various heavy processing tasks.

Later on in 2011, the OTB Applications has been further revamped. Because of the increasing need to interface the OTB Applications into other software and to provide auto-generated interfaces, the Orfeo Toolbox development team decided to develop a new application framework. The main idea of this framework is the following: each application is written once for all in a shared library (also known as plugin). This plugin can be auto-loaded into appropriate tools wihtout recompiling, and is able to fully describe its parameters, behaviour and documentation.

The tools to use the plugins can be extended, but Orfeo Toolbox shipped the following:

  • A command-line laucher, which is almost equivalent to the former OTB Applications command-line interface,
  • A graphical launcher, with an auto-generated QT interface, providing ergonomic parameters setting, display of documentation, and progress reporting,
  • A SWIG interface, which means that any application can be loaded set-up and executed into a high-level language such as Python or Java for instance.

Additionally, QGis plugins built on top of the SWIG/Python interface are available with seamless integration within QGis. You can find a short guide about it here .

To facilitate the use of these tools and applications, they will now be shipped with the standard Orfeo Toolbox package. It means that the former OTB-Applications package has entered its maintenance cycle : no new feature will be pushed there, and all development is done directly inside the Orfeo Toolbox package.

The OTB Applications are now rich of more than 40 tools, which are listed in the the applications reference documentation, presented in chapter [chap:apprefdoc], page .

Using the applications

Using the new framework is slightly more complex than launching a command-line tool. This section describes all the ways to launch the new applications. Apart from the simplified access, which is similar to the former access to , you will need to know the application name and optionally the path where the applications plugins are stored. For applications shipped with , the name of each application can be found in chapter [chap:apprefdoc], page .

Simplified use

All standard applications delivered in with comes with simplified scripts in the system path, allowing to launch the command-line and graphical user interface versions of the application in the same simple way we used to launch the old applications. The command-line interface is prefixed by otbcli_, while the Qt interface is prefixed by otbgui_. For instance, calling otbcli_Convert will launch the command-line interface of the Convert application, while otbgui_Convert will launch its GUI.

Passing arguments to the command-line version (prefixed by otbcli_) is explained in next sub-section.

Using the command-line launcher

The command-line application launcher allows to load an application plugin, to set its parameters, and execute it using the command line. Launching the otbApplicationLauncherCommandLine without argument results in the following help to be displayed:

$ otbApplicationLauncherCommandLine
Usage : ./otbApplicationLauncherCommandLine module_name [MODULEPATH] [arguments]

The module_name parameter corresponds to the application name. The [MODULEPATH] argument is optional and allows to pass to the launcher a path where the shared library (or plugin) corresponding to module_name is.

It is also possible to set this path with the environment variable OTB_APPLICATION_PATH, making the [MODULEPATH] optional. This variable is checked by default when no [MODULEPATH] argument is given. When using multiple paths in OTB_APPLICATION_PATH, one must make sure to use the standard path separator of the target system, which is : on Unix, and ; on Windows.

An error in the application name (i.e. in parameter module_name) will make the otbApplicationLauncherCommandLine lists the name of all applications found in the available path (either [MODULEPATH] and/or OTB_APPLICATION_PATH).

To ease the use of the applications, and try avoiding extensive environment customization, ready-to-use scripts are provided by the OTB installation to launch each application, and takes care of adding the standard application installation path to the OTB_APPLICATION_PATH environment variable.

These scripts are named otbcli_<ApplicationName> and do not need any path settings. For example you can start the Orthorectification application with the script called otbcli_Orthorectification.

Launching an application with no or incomplete parameters will make the launcher display a summary of the parameters, indicating the mandatory parameters missing to allow for application execution. Here is an example with the OrthoRectification application:

$ otbcli_OrthoRectification

ERROR: Waiting for at least one parameter...

====================== HELP CONTEXT ======================
NAME: OrthoRectification
DESCRIPTION: This application allows to ortho-rectify optical images from supported sensors.

otbcli_OrthoRectification -io.in QB_TOULOUSE_MUL_Extract_500_500.tif -io.out QB_Toulouse_ortho.tif

DOCUMENTATION: http://www.orfeo-toolbox.org/Applications/OrthoRectification.html
======================= PARAMETERS =======================
        -progress                        <boolean>        Report progress
MISSING -io.in                           <string>         Input Image
MISSING -io.out                          <string> [pixel] Output Image  [pixel=uint8/int8/uint16/int16/uint32/int32/float/double]
        -map                             <string>         Output Map Projection [utm/lambert2/lambert93/transmercator/wgs/epsg]
MISSING -map.utm.zone                    <int32>          Zone number
        -map.utm.northhem                <boolean>        Northern Hemisphere
        -map.transmercator.falseeasting  <float>          False easting
        -map.transmercator.falsenorthing <float>          False northing
        -map.transmercator.scale         <float>          Scale factor
        -map.epsg.code                   <int32>          EPSG Code
        -outputs.mode                    <string>         Parameters estimation modes [auto/autosize/autospacing]
MISSING -outputs.ulx                     <float>          Upper Left X
MISSING -outputs.uly                     <float>          Upper Left Y
MISSING -outputs.sizex                   <int32>          Size X
MISSING -outputs.sizey                   <int32>          Size Y
MISSING -outputs.spacingx                <float>          Pixel Size X
MISSING -outputs.spacingy                <float>          Pixel Size Y
        -outputs.isotropic               <boolean>        Force isotropic spacing by default
        -elev.dem                        <string>         DEM directory
        -elev.geoid                      <string>         Geoid File
        -elev.default                    <float>          Average Elevation
        -interpolator                    <string>         Interpolation [nn/linear/bco]
        -interpolator.bco.radius         <int32>          Radius for bicubic interpolation
        -opt.rpc                         <int32>          RPC modeling (points per axis)
        -opt.ram                         <int32>          Available memory for processing (in MB)
        -opt.gridspacing                 <float>          Resampling grid spacing

For a detailed description of the application behaviour and parameters, please check the application reference documentation presented chapter [chap:apprefdoc], page  or follow the DOCUMENTATION hyperlink provided in otbApplicationLauncherCommandLine output. Parameters are passed to the application using the parameter key (which might include one or several . character), prefixed by a -. Command-line examples are provided in chapter [chap:apprefdoc], page .

Using the GUI launcher

The graphical interface for the applications provides a usefull interactive user interface to set the parameters, choose files, and monitor the execution progress.

This interface can be activated through the CMake option .

This launcher needs the same two arguments as the command line launcher :

$ otbApplicationLauncherQt module_name [MODULEPATH]

The application paths can be set with the OTB_APPLICATION_PATH environment variable, as for the command line launcher. Also, as for the command-line application, a more simple script is generated and installed by OTB to ease the configuration of the module path : to launch the graphical user interface, one will start the otbgui_Rescale script.

The resulting graphical application displays a window with several tabs:

  • Parameters is where you set the parameters and execute the application.
  • Logs is where you see the informations given by the application during its execution.
  • Progress is where you see a progress bar of the execution (not available for all applications).
  • Documentation is where you find a summary of the application documentation.

In this interface, every optional parameter has a check box that you have to tick if you want to set a value and use this parameter. The mandatory parameters cannot be unchecked.

The interface of the application is shown here as an example.


Using the Python interface

The applications can also be accessed from Python, through a module named otbApplication

On Unix systems it is typically available in the /usr/lib/otb/python directory. You may need to configure the environment variable PYTHONPATH to include this directory so that the module becomes available from an Python shell.

On Windows, you can install the otb-python package, and the module will be available from an OSGeo4W shell automatically.

In this module, two main classes can be manipulated :

  • Registry, which provides access to the list of available applications, and can create applications
  • Application, the base class for all applications. This allows to interact with an application instance created by the Registry

As for the command line and GUI launchers, the path to the application modules needs to be properly set with the OTB_APPLICATION_PATH environment variable. The standard location on Unix systems is /usr/lib/otb/applications. On Windows, the applications are available in the otb-bin OSGeo4W package, and the environment is configured automatically so you don’t need to tweak OTB_APPLICATION_PATH.

Here is one example of how to use Python to run the Smoothing application, changing the algorithm at each iteration.

#  Example on the use of the Smoothing application

# We will use sys.argv to retrieve arguments from the command line.
# Here, the script will accept an image file as first argument,
# and the basename of the output files, without extension.
from sys import argv

# The python module providing access to OTB applications is otbApplication
import otbApplication

# otbApplication.Registry can tell you what application are available
print "Available applications : "
print str( otbApplication.Registry.GetAvailableApplications() )

# Let's create the application with codename "Smoothing"
app = otbApplication.Registry.CreateApplication("Smoothing")

# We print the keys of all its parameter
print app.GetParametersKeys()

# First, we set the input image filename
app.SetParameterString("in", argv[1])

# The smoothing algorithm can be set with the "type" parameter key
# and can take 3 values : 'mean', 'gaussian', 'anidif'
for type in ['mean', 'gaussian', 'anidif']:

  print 'Running with ' + type + ' smoothing type'

  # Here we configure the smoothing algorithm
  app.SetParameterString("type", type)

  # Set the output filename, using the algorithm to differenciate the outputs
  app.SetParameterString("out", argv[2] + type + ".tif")

  # This will execute the application and save the output file

Load/Save OTB-Applications parameters from/to file

Since OTB 3.20, OTB applications parameters can be export/import to/from an XML file using inxml/outxml parameters. Those parameters are available in all applications.

An example is worth a thousand words

otbcli_BandMath -il input_image_1 input_image_2
                -exp "abs(im1b1 - im2b1)"
                -out output_image
                -outxml saved_applications_parameters.xml

Then, you can run the applications with the same parameters using the output xml file previously saved. For this, you have to use the inxml parameter:

otbcli_BandMath -inxml saved_applications_parameters.xml

Note that you can also overload parameters from command line at the same time

otbcli_BandMath -inxml saved_applications_parameters.xml
                -exp "(im1b1 - im2b1)"

In this cas it will use as mathematical expression “(im1b1 - im2b1)” instead of “abs(im1b1 - im2b1)”.

Finally, you can also launch applications directly from the command-line launcher executable using the inxml parameter without having to declare the application name. Use in this case:

otbApplicationLauncherCommandLine -inxml saved_applications_parameters.xml

It will retrieve the application name and related parameters from the input xml file and launch in this case the BandMath applications.

Using OTB from QGIS

The processing toolbox

OTB applications are available from QGIS. Use them from the processing toolbox, which is accessible with Processing \(\rightarrow\) Toolbox. Switch to “advanced interface” in the bottom of the application widget and OTB applications will be there.


Using a custom OTB

If QGIS cannot find OTB, the “applications folder” and “binaries folder” can be set from the settings in the Processing \(\rightarrow\) Settings \(\rightarrow\) “service provider”.


On some versions of QGIS, if an existing OTB installation is found, the textfield settings will not be shown. To use a custom OTB instead of the existing one, you will need to replace the otbcli, otbgui and library files in QGIS installation directly.