4.4.8 Ortho-rectification
This application allows ortho-rectification of optical images from supported sensors.
Detailed description
An inverse sensor model is built from the input image metadata to convert geographical to raw geometry
coordinates. This inverse sensor model is then combined with the chosen map projection to build a global
coordinate mapping grid. Last, this grid is used to resample using the chosen interpolation
algorithm. A Digital Elevation Model can be specified to account for terrain deformations.
In case of SPOT5 images, the sensor model can be approximated by an RPC model in order to speed-up
computation.
Parameters
This section describes in details the parameters available for this application. Table 4.58, page 531
presents a summary of these parameters and the parameters keys to be used in command-line and
programming languages. Application key is OrthoRectification.
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Parameter key | Parameter type |
Parameter description |
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io | Group |
Input and output data |
io.in | Input image |
Input Image |
io.out | Output image |
Output Image |
map | Choices |
Output Cartographic Map Projection |
map utm | Choice |
Universal Trans-Mercator (UTM) |
map lambert2 | Choice |
Lambert II Etendu |
map lambert93 | Choice |
Lambert93 |
map wgs | Choice |
WGS 84 |
map epsg | Choice |
EPSG Code |
map.utm.zone | Int |
Zone number |
map.utm.northhem | Boolean |
Northern Hemisphere |
map.epsg.code | Int |
EPSG Code |
outputs | Group |
Output Image Grid |
outputs.mode | Choices |
Parameters estimation modes |
outputs.mode auto | Choice |
User Defined |
outputs.mode autosize | Choice |
Automatic Size from Spacing |
outputs.mode autospacing | Choice |
Automatic Spacing from Size |
outputs.mode outputroi | Choice |
Automatic Size from Spacing and
output corners |
outputs.mode orthofit | Choice |
Fit to ortho |
outputs.ulx | Float |
Upper Left X |
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outputs.uly | Float |
Upper Left Y |
outputs.sizex | Int |
Size X |
outputs.sizey | Int |
Size Y |
outputs.spacingx | Float |
Pixel Size X |
outputs.spacingy | Float |
Pixel Size Y |
outputs.lrx | Float |
Lower right X |
outputs.lry | Float |
Lower right Y |
outputs.ortho | Input image |
Model ortho-image |
outputs.isotropic | Boolean |
Force isotropic spacing by default |
outputs.default | Float |
Default pixel value |
elev | Group |
Elevation management |
elev.dem | Directory |
DEM directory |
elev.geoid | Input File name |
Geoid File |
elev.default | Float |
Default elevation |
interpolator | Choices |
Interpolation |
interpolator bco | Choice |
Bicubic interpolation |
interpolator nn | Choice |
Nearest Neighbor interpolation |
interpolator linear | Choice |
Linear interpolation |
interpolator.bco.radius | Int |
Radius for bicubic interpolation |
opt | Group |
Speed optimization parameters |
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opt.rpc | Int |
RPC modeling (points per axis) |
opt.ram | Int |
Available RAM (Mb) |
opt.gridspacing | Float |
Resampling grid spacing |
inxml | XML input parameters file |
Load otb application from xml file |
outxml | XML output parameters file |
Save otb application to xml file |
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Table 4.58: Parameters table for Ortho-rectification.
Input and output data
This group of parameters allows setting the input and output images.
- Input Image: The input image to ortho-rectify
- Output Image: The ortho-rectified output image
Output Cartographic Map Projection
Parameters of the output map projection to be used. Available choices are:
- Universal Trans-Mercator (UTM): A system of transverse mercator projections dividing the surface
of Earth between 80S and 84N latitude.
- Zone number: The zone number ranges from 1 to 60 and allows defining the transverse
mercator projection (along with the hemisphere)
- Northern Hemisphere: The transverse mercator projections are defined by their zone
number as well as the hemisphere. Activate this parameter if your image is in the
northern hemisphere.
- Lambert II Etendu: This is a Lambert Conformal Conic projection mainly used in France.
- Lambert93: This is a Lambert 93 projection mainly used in France.
- WGS 84: This is a Geographical projection
- EPSG Code: This code is a generic way of identifying map projections, and allows specifying a large
amount of them. See www.spatialreference.org to find which EPSG code is associated to your
projection;
- EPSG Code: See www.spatialreference.org to find which EPSG code is associated to
your projection
Output Image Grid
This group of parameters allows one to define the grid on which the input image will be resampled.
- Parameters estimation modes:
Available choices are:
- User Defined: This mode allows you to fully modify default values.
- Automatic Size from Spacing: This mode allows you to automatically compute the
optimal image size from given spacing (pixel size) values
- Automatic Spacing from Size: This mode allows you to automatically compute the
optimal image spacing (pixel size) from the given size
- Automatic Size from Spacing and output corners: This mode allows you to
automatically compute the optimal image size from spacing (pixel size) and output
corners
- Fit to ortho: Fit the size, origin and spacing to an existing ortho image (uses the value
of outputs.ortho)
- Upper Left X: Cartographic X coordinate of upper-left corner (meters for cartographic projections,
degrees for geographic ones)
- Upper Left Y: Cartographic Y coordinate of the upper-left corner (meters for cartographic
projections, degrees for geographic ones)
- Size X: Size of projected image along X (in pixels)
- Size Y: Size of projected image along Y (in pixels)
- Pixel Size X: Size of each pixel along X axis (meters for cartographic projections, degrees for
geographic ones)
- Pixel Size Y: Size of each pixel along Y axis (meters for cartographic projections, degrees for
geographic ones)
- Lower right X: Cartographic X coordinate of the lower-right corner (meters for cartographic
projections, degrees for geographic ones)
- Lower right Y: Cartographic Y coordinate of the lower-right corner (meters for cartographic
projections, degrees for geographic ones)
- Model ortho-image: A model ortho-image that can be used to compute size, origin and spacing of
the output
- Force isotropic spacing by default: Default spacing (pixel size) values are estimated from the
sensor modeling of the image. It can therefore result in a non-isotropic spacing. This
option allows you to force default values to be isotropic (in this case, the minimum of
spacing in both direction is applied. Values overridden by user are not affected by this
option.
- Default pixel value: Default value to write when outside of input image.
Elevation management
This group of parameters allows managing elevation values. Supported formats are SRTM, DTED or any
geotiff. DownloadSRTMTiles application could be a useful tool to list/download tiles related to a
product.
- DEM directory: This parameter allows selecting a directory containing Digital Elevation
Model tiles
- Geoid File: Use a geoid grid to get the height above the ellipsoid in case
there is no DEM available, no coverage for some points or pixels with no_data
in the DEM tiles. A version of the geoid can be found on the OTB website
(http://hg.orfeo-toolbox.org/OTB-Data/raw-file/404aa6e4b3e0/Input/DEM/egm96.grd).
- Default elevation: This parameter allows setting the default height above ellipsoid when
there is no DEM available, no coverage for some points or pixels with no_data in the DEM
tiles, and no geoid file has been set. This is also used by some application as an average
elevation value.
Interpolation
This group of parameters allows one to define how the input image will be interpolated during resampling.
Available choices are:
- Bicubic interpolation
- Radius for bicubic interpolation: This parameter allows one to control the size of
the bicubic interpolation filter. If the target pixel size is higher than the input pixel size,
increasing this parameter will reduce aliasing artefacts.
- Nearest Neighbor interpolation: Nearest neighbor interpolation leads to poor image quality, but it is
very fast.
- Linear interpolation: Linear interpolation leads to average image quality but is quite
fast
Speed optimization parameters
This group of parameters allows optimization of processing time.
- RPC modeling (points per axis): Enabling RPC modeling allows one to speed-up SPOT5
ortho-rectification. Value is the number of control points per axis for RPC estimation
- Available RAM (Mb): This allows setting the maximum amount of RAM available for
processing. As the writing task is time consuming, it is better to write large pieces of data,
which can be achieved by increasing this parameter (pay attention to your system capabilities)
- Resampling grid spacing: Resampling is done according to a coordinate mapping
deformation grid, whose pixel size is set by this parameter, and expressed in the coordinate
system of the output image The closer to the output spacing this parameter is, the more precise
will be the ortho-rectified image,but increasing this parameter will reduce processing time.
Load otb application from xml file
Load otb application from xml file
Save otb application to xml file
Save otb application to xml file
Example
To run this example in command-line, use the following:
otbcli_OrthoRectification -io.in QB_TOULOUSE_MUL_Extract_500_500.tif -io.out QB_Toulouse_ortho.tif
To run this example from Python, use the following code snippet:
#!/usr/bin/python # Import the otb applications package import otbApplication # The following line creates an instance of the OrthoRectification application OrthoRectification = otbApplication.Registry.CreateApplication("OrthoRectification") # The following lines set all the application parameters: OrthoRectification.SetParameterString("io.in", "QB_TOULOUSE_MUL_Extract_500_500.tif") OrthoRectification.SetParameterString("io.out", "QB_Toulouse_ortho.tif") # The following line execute the application OrthoRectification.ExecuteAndWriteOutput()
Limitations
Supported sensors are Pleiades, SPOT5 (TIF format), Ikonos, Quickbird, Worldview2, GeoEye.
Authors
This application has been written by OTB-Team.
See also
These additional ressources can be useful for further information:
- Ortho-rectification chapter from the OTB Software Guide