StereoRectificationGridGenerator - Stereo-rectification deformation grid generator¶

Generates two deformation fields to resample in epipolar geometry, a pair of stereo images up to the sensor model precision

Detailed description¶

This application generates a pair of deformation grid to stereo-rectify a pair of stereo images according to sensor modelling and a mean elevation hypothesis.

This application is the first part of the stereo reconstruction framework. The output deformation grids can be passed to the GridBasedImageResampling application for actual resampling into epipolar geometry.

There are several ways to set the elevation source:

An arbitrary constant elevation
A DEM directory
Compute an average elevation from a DEM

If needed, the application can compute inverse resampling grids (from epipolar to original sensor geometry). Don’t forget to check the other outputs from the application. For instance, the application gives the X and Y size of the rectified images, along with an estimated baseline ratio.

Parameters¶

This section describes in details the parameters available for this application. Table [1] presents a summary of these parameters and the parameters keys to be used in command-line and programming languages. Application key is StereoRectificationGridGenerator .

[1]	Table: Parameters table for Stereo-rectification deformation grid generator.

Parameter Key	Parameter Name	Parameter Type
io	Input and output data	Group
io.inleft	Left input image	Input image
io.inright	Right input image	Input image
io.outleft	Left output deformation grid	Output image
io.outright	Right output deformation grid	Output image
epi	Epipolar geometry and grid parameters	Group
epi.elevation	Elevation management	Group
epi.elevation.dem	DEM directory	Directory
epi.elevation.geoid	Geoid File	Input File name
epi.elevation.default	Default elevation	Float
epi.elevation.avgdem	Average elevation computed from DEM	Group
epi.elevation.avgdem.step	Sub-sampling step	Int
epi.elevation.avgdem.value	Average elevation value	Float
epi.elevation.avgdem.mindisp	Minimum disparity from DEM	Float
epi.elevation.avgdem.maxdisp	Maximum disparity from DEM	Float
epi.scale	Scale of epipolar images	Float
epi.step	Step of the deformation grid (in nb. of pixels)	Int
epi.rectsizex	Rectified image size X	Int
epi.rectsizey	Rectified image size Y	Int
epi.baseline	Mean baseline ratio	Float
inverse	Write inverse fields	Group
inverse.outleft	Left inverse deformation grid	Output image
inverse.outright	Right inverse deformation grid	Output image
inverse.ssrate	Sub-sampling rate for inversion	Int
inxml	Load otb application from xml file	XML input parameters file
outxml	Save otb application to xml file	XML output parameters file

[Input and output data]: This group of parameters allows setting the input and output images.

Left input image: The left image from the stereo pair, in sensor geometry.
Right input image: The right image from the stereo pair, in sensor geometry.
Left output deformation grid: The deformation grid to resample the left image from sensor geometry to epipolar geometry.
Right output deformation grid: The deformation grid to resample the right image from sensor geometry to epipolar geometry.

[Epipolar geometry and grid parameters]: Parameters of the epipolar geometry and output grids.

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 files. Note that this directory should contain only DEM files. Unexpected behaviour might occurs if other images are found in this directory.

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(https://gitlab.orfeo-toolbox.org/orfeotoolbox/otb-data/blob/master/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.

Average elevation computed from DEM: Average elevation computed from the provided DEM.

Sub-sampling step: Step of sub-sampling for average elevation estimation.

Average elevation value: Average elevation value estimated from DEM.

Minimum disparity from DEM: Disparity corresponding to estimated minimum elevation over the left image.

Maximum disparity from DEM: Disparity corresponding to estimated maximum elevation over the left image.

Scale of epipolar images: The scale parameter allows generating zoomed-in (scale < 1) or zoomed-out (scale > 1) epipolar images.
Step of the deformation grid (in nb. of pixels): Stereo-rectification deformation grid only varies slowly. Therefore, it is recommended to use a coarser grid (higher step value) in case of large images.
Rectified image size X: The application computes the optimal rectified image size so that the whole left input image fits into the rectified area. However, due to the scale and step parameter, this size may not match the size of the deformation field output. In this case, one can use these output values.
Rectified image size Y: The application computes the optimal rectified image size so that the whole left input image fits into the rectified area. However, due to the scale and step parameter, this size may not match the size of the deformation field output. In this case, one can use these output values.
Mean baseline ratio: This parameter is the mean value, in pixels.meters^-1, of the baseline to sensor altitude ratio. It can be used to convert disparities to physical elevation, since a disparity of one pixel will correspond to an elevation offset of the invert of this value with respect to the mean elevation.

[Write inverse fields]: This group of parameter allows generating the inverse fields as well.

Left inverse deformation grid: The deformation grid to resample the left image from the epipolar geometry back into its original sensor geometry.
Right inverse deformation grid: The output deformation grid to resample the right image from the epipolar geometry back into its original sensor geometry.
Sub-sampling rate for inversion: Grid inversion is an heavy process that implies spline regression on control points. To avoid eating to much memory, this parameter allows one to first sub-sample the field to invert.

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_StereoRectificationGridGenerator -io.inleft wv2_xs_left.tif -io.inright wv2_xs_left.tif -io.outleft wv2_xs_left_epi_field.tif -io.outright wv2_xs_right_epi_field.tif -epi.elevation.default 400

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 StereoRectificationGridGenerator application
StereoRectificationGridGenerator = otbApplication.Registry.CreateApplication("StereoRectificationGridGenerator")

# The following lines set all the application parameters:
StereoRectificationGridGenerator.SetParameterString("io.inleft", "wv2_xs_left.tif")

StereoRectificationGridGenerator.SetParameterString("io.inright", "wv2_xs_left.tif")

StereoRectificationGridGenerator.SetParameterString("io.outleft", "wv2_xs_left_epi_field.tif")

StereoRectificationGridGenerator.SetParameterString("io.outright", "wv2_xs_right_epi_field.tif")

StereoRectificationGridGenerator.SetParameterFloat("epi.elevation.default", 400)

# The following line execute the application
StereoRectificationGridGenerator.ExecuteAndWriteOutput()

Limitations¶

Generation of the deformation grid is not streamable, pay attention to this fact when setting the grid step.

Authors¶

This application has been written by OTB-Team.