DisparityMapToElevationMap - Disparity map to elevation map¶

Projects a disparity map into a regular elevation map.

Detailed description¶

This application uses a disparity map computed from a stereo image pair to produce an elevation map on the ground area covered by the stereo pair.

This application is part of the stereo reconstruction pipeline. It can be used after having computed the disparity map with BlockMatching.

The needed inputs are

:the disparity map, the stereo pair (in original geometry) and the epipolar deformation grids. These grids (computed by StereoRectificationGridGenerator) have to contain the transform between the original geometry (stereo pair) and the epipolar geometry (disparity map). The algorithm for each disparity is the following :

skip if position is discarded by the disparity mask
compute left ray : transform the current position from epipolar geometry to left sensor geometry (left rectification grid)
compute right ray : shift the current position with current disparity and transform from epipolar geometry to right sensor (right rectification grid)
estimate best 3D intersection between left and right rays
for the ground cell of the obtained 3D point, keep its elevation if greater than current elevation (keeps the maximum of elevations of all 3D points in each cell)

Minimum and maximum elevations settings are here to bound the reconstructed DEM.

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 DisparityMapToElevationMap .

[1]	Table: Parameters table for Disparity map to elevation map.

Parameter Key	Parameter Name	Parameter Type
io	Input and output data	Group
io.in	Input disparity map	Input image
io.left	Left sensor image	Input image
io.right	Right sensor image	Input image
io.lgrid	Left Grid	Input image
io.rgrid	Right Grid	Input image
io.out	Output elevation map	Output image
io.mask	Disparity mask	Input image
step	DEM step	Float
hmin	Minimum elevation expected	Float
hmax	Maximum elevation expected	Float
elev	Elevation management	Group
elev.dem	DEM directory	Directory
elev.geoid	Geoid File	Input File name
elev.default	Default elevation	Float
ram	Available RAM (Mb)	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 one to set input images, output images and grids.

Input disparity map: The input disparity map (horizontal disparity in first band, vertical in second). This map can be computed by BlockMatching application.
Left sensor image: Left image in original (sensor) geometry. Only the geometric model of this image will be used, not the pixel values.
Right sensor image: Right image in original (sensor) geometry. Only the geometric model of this image will be used, not the pixel values.
Left Grid: Left epipolar grid (deformation grid between left sensor et disparity spaces).
Right Grid: Right epipolar grid (deformation grid between right sensor et disparity spaces).
Output elevation map: Output elevation map in ground projection. Elevation values are in meters. Floating point pixel type are expected.
Disparity mask: Masked disparity pixels won’t be projected (mask values equal to zero).

DEM step: Spacing of the output elevation map (in meters).

Minimum elevation expected: Minimum elevation expected (in meters).

Maximum elevation expected: Maximum elevation expected (in meters).

[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.

Available RAM (Mb): Available memory for processing (in MB).

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_DisparityMapToElevationMap -io.in disparity.tif -io.left sensor_left.tif -io.right sensor_right.tif -io.lgrid grid_epi_left.tif -io.rgrid grid_epi_right.tif -io.out dem.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 DisparityMapToElevationMap application
DisparityMapToElevationMap = otbApplication.Registry.CreateApplication("DisparityMapToElevationMap")

# The following lines set all the application parameters:
DisparityMapToElevationMap.SetParameterString("io.in", "disparity.tif")

DisparityMapToElevationMap.SetParameterString("io.left", "sensor_left.tif")

DisparityMapToElevationMap.SetParameterString("io.right", "sensor_right.tif")

DisparityMapToElevationMap.SetParameterString("io.lgrid", "grid_epi_left.tif")

DisparityMapToElevationMap.SetParameterString("io.rgrid", "grid_epi_right.tif")

DisparityMapToElevationMap.SetParameterString("io.out", "dem.tif")

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

Limitations¶

The epipolar deformation grid should be able to entirely fit in memory.

Authors¶

This application has been written by OTB-Team.