How to measure distances in the image?

Question

Let's say we have an image like this

_{(source: curiousexpeditions.org )}

Suppose we have already used filters and the edge detection algorithm in this figure. Now my goal is to measure distances (NOT real distances, the distance can be in any arbitrary unit). For example: how do I find the length of the hall? (to the window)

Or the height of the bookshelves? How exactly do you place the “scale” and measure. I am looking for ideas. However, it would be helpful if the answers were from an OpenCV perspective.

Answer 1

It depends on what you are trying to do.

, . , "", , , , - . "", , . (x ^ 2 + y ^ 2 = z ^ 2)

, , , , - , , . . 2D → 3D-: 2D-, . 3- , , 3 (X, y, z) 2 .

OpenCV, (, ). - . google " "

Answer 2

, , , . , X Y%. . .

. :
http://en.wikipedia.org/wiki/Slope
http://en.wikipedia.org/wiki/Cartesian_coordinate_system