What are the algorithms for determining the relative distance from an image?

Question

Algorithms

I want to put a camera on the robot and use it, in addition to the main purpose, as a distance sensor
I don’t need the exact distance, I need to determine the obstacle at the level so that the robot simply doesn’t collide with it
I know that there are algorithms for two cameras, but to accurately fix them at home, I think, almost impossible

Answer 1

It seems to me that this will work fine only if you apply a coordinate grid everywhere, then knowing the characteristics of the lens of even one camera, you can calculate something.
And two cameras do not have to be fixed perfectly, you just need some kind of object, perhaps a lined cube, by which you can calculate the correction factors.
Without a grid, the algorithm can apparently only react to a sharp change in shadows / highlights relative to the floor. Two cameras aren't much better than one unless they're far apart.

Answer 2

Instead of two cameras, you can use one and a pair of mirrors. And all algorithms for a two-chamber system.