What does scan_height do?

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We are using the scan_height parameter and it seems like nothing is changing at all. From the description we thought that the parameter would change the number of rows being looked at for the scan, thus allowing us to get the minimum distance to an obstacle at desired heights.

Here is the command we are using to run in the terminal:

rosrun depthimage_to_laserscan depthimage_to_larscan image:=camera/depth/image_raw _scan_height:400

Thanks!