I wonder if I can get the height of an object (tree or a building) with the knowledge of:
The distance between me and the object?
The apparent height of that object?
You can hold a ruler or meter stick (real or imaginary) at the end of your arm.
Suppose you are 50 meters away from the object, and suppose your arm is 1 meter long.
Then take the height of the object as it appears on the ruler, and multiply by 50.