How do I extract real life distances from a Depth Map TIFF file created via iOS?

I have some depth map files in TIFF format that I am trying to extract data from programmatically. I see that I can import TIFF format images with NSImage, and from there, can get the raw pixel data. But how do I convert this to real distances? Any help would be appreciated, thanks!

How do I extract real life distances from a Depth Map TIFF file created via iOS?
 
 
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