Stereo Vision Distance from Disparity Accuracy Measurement Testing

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Hi,

SO I have successfully managed to calibrate my two stereo cameras and thery are running the stereo_image_proc. I am able to view the disparity image stream generated using the image_view node. Before moving onto any mapping I would like to run an experiment on the disparity images in order to check the accuracy and range of the distance by using the values generated by stereo_image_proc node.

I would like to take a series of images at a known of a textured box positioned at a different known distances of a particular range. What would be the best approach for me to calculate the depth? Here are my ideas but I dont know if they are in right or not:

1. Write a C++ subscriber to the stereo_msgs::DisparityImage topic which then takes the disparity image and the f (focal length) and T(baseline) parameters. Converts the disparity image into OpenCV format so that I can calculate the depth for each pixel (disparity) value using the formula z = fT/d and then map the calculated distances on an array or an OpenCV image which can then be indexed to extract a specific distance.

   2.Write a C++ Subscriber that attempts at extracting the z cordinate value from either the stereo_msgs::pointcloud or stereo_msgs::pointcloud2 topic for a corresponding x and y coordinate.

Apologies if this has already been discussed but ive looked around and havn't found a solution, or maybe im going at it the completely wrong way. I would really appreciate some help.

Thanks