Check the example below, please.
1) Indirect Measurement in geometry is a method that evolves the measurement of something with the help of some properties like similarity, trig ratios.
2) Imagine that, there is a tree that is 10 ft away from point A and the peak of the tree makes to the ground is 60º, so we can find the measure of the tree with an indirect measure, considering that the man is 5 ft away from point A with a 60º angle of elevation.
Using similarity properties we can find the height of that tree if the man and the tree are proportionally distant to point A, and the angle of elevation is the same.