Repository: opencv
Issue: Tutorial example "Depth map from stereo images" calculates disparity, not depth map
Labels: category: documentation

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##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
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- OpenCV => 4.5
- Operating System / Platform => N/A
- Compiler => N/A

##### Detailed description

The [depth map from stereo images tutorial](https://docs.opencv.org/4.5.2/dd/d53/tutorial_py_depthmap.html) calculates the disparity map but does not calculate the depth map.  Recommend the example be modified to also calculate and display the depth map.

Also, in general, could the opencv documentation be improved by including verifiable information.  In this example, the images essentially contain a collection of objects.  The image provides no verifiable information of the solution (depth map).  By just adding three rulers, arranged parallel, and horizontally perpendicular and vertically perpendicular to the camera, along with the measured distanced from the camera to the rulers, and displaying the depth values at the image locations of the ruler tick marks would provide insight into the conversion to measurable units and to the accuracy of the depth map values.  And a brief discussion of the degree of agreement between measured and estimated values would be useful.  

##### Steps to reproduce

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