In junior high school maths, there are usually questions about measuring the angle of depression and/or distance using trigonometry. Common examples could be like "Find the angle of depression from a lighthouse beacon 112 m above the sea level to a boat that is at a horizontal distance of 1.5 km from the lighthouse". A picture (not to scale) may be given as the one on the right. But then, what if the scenario is in 3D?
