# reconstructScene

Reconstruct 3-D scene from disparity map

## Description

example

xyzPoints = reconstructScene(disparityMap,reprojectionMatrix) returns an array of 3-D world point coordinates that reconstruct a scene from a disparity map. The 3-D world coordinates are relative to the optical center of camera 1 in a stereo system. You can use the rectifyStereoImages function to obtain the reprojectionMatrix from a pair of stereo images.

## Examples

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Read in the stereo pair of images.

Rectify the images.

[J1, J2, reprojectionMatrix] = rectifyStereoImages(I1,I2,stereoParams);

Display the images after rectification.

figure
imshow(cat(3,J1(:,:,1),J2(:,:,2:3)),'InitialMagnification',50);

Compute the disparity.

disparityMap = disparitySGM(im2gray(J1),im2gray(J2));
figure
imshow(disparityMap,[0,64],'InitialMagnification',50);

Reconstruct the 3-D world coordinates of points corresponding to each pixel from the disparity map.

xyzPoints = reconstructScene(disparityMap,reprojectionMatrix);

Segment out a person located between 3.2 and 3.7 meters away from the camera.

Z = xyzPoints(:,:,3);
mask = repmat(Z > 3200 & Z < 3700,[1,1,3]);
imshow(J1,'InitialMagnification',50);

## Input Arguments

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Disparity image, specified as a 2-D array of disparity values for pixels in image 1 of a stereo pair. You can use either disparityBM or disparitySGM functions to generate the disparity image.

The disparity image can contain invalid values marked as NaN. These values correspond to pixels in image 1 that did not match with image 2. The function sets the world coordinates corresponding to invalid disparity value to NaN.

Pixels with zero disparity correspond to world points that are too far away to measure, given the resolution of the camera. The function sets the world coordinates corresponding to zero disparity to Inf.

When you specify the disparityMap input as a double, the function returns the coordinates as double. Otherwise, the function returns the coordinates as single.

Data Types: single | double

Reprojection matrix, specified as a 4-by-4 matrix. You can use the rectifyStereoImages function to obtain the reprojectionMatrix from a pair of stereo images.

The reprojection matrix is represented as:

$\left[\begin{array}{cccc}1& 0& 0& -cx\\ 0& 1& 0& -cy\\ 0& 0& 0& f\\ 0& 0& 1/b& 0\end{array}\right]$

where f and [cx,cy] are the focal length and principal point of the rectified camera 1, respectively. b is the baseline of the virtual rectified stereo camera.

Data Types: single | double

## Output Arguments

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Coordinates of world points, returned as an M-by-N-by-3 array. The 3-D world coordinates are relative to the optical center of camera 1 in the stereo system represented by stereoParams.

The output array contains the [x, y, z] coordinates of world points that correspond to the pixels in the disparityMap input. xyzPoints(:, :, 1) contains the x world coordinates of points corresponding to the pixels in the disparity map. xyzPoints(:, :, 2) contains the y world coordinates, and xyzPoints(:, :, 3) contains the z world coordinates. The 3-D world coordinates are relative to the optical center of camera 1 in the stereo system.

When you specify the disparityMap input as double, the function returns the xyzPoints output as double. Otherwise, the function returns it as single.

Data Types: single | double

## References

[1] G. Bradski and A. Kaehler, Learning OpenCV : Computer Vision with the OpenCV Library, Sebastopol, CA: O'Reilly, 2008.

## Version History

Introduced in R2014a