Is the angle of depression the same as the angle of elevation?

The angle of depression measured from the higher point equals the angle of elevation measured from the lower point looking back up, because the two horizontal reference lines are parallel and the sight line is a transversal (alternate interior angles). The two angles are equal in size but measured from opposite ends of the same sight line.

What instrument measures the angle of depression on site?

Surveyors typically use a clinometer, an inclinometer, or a total station to measure the angle of depression (or elevation) directly on site, rather than calculating it from separately measured distances.

When would a Gibraltar building site actually need an angle of depression?

Beyond classroom trigonometry, it comes up when checking sightlines on the Rock's steep terrain, estimating the fall between two survey points, or a rough clearance check before a licensed surveyor carries out a precise measurement with a total station.

Angle of Depression Calculator — Sightline Angle | Gibraltar

Angle of Depression Calculator: Sightline Angle from Height & Distance

The angle of depression is the angle between a horizontal line of sight and a downward line to a lower point — the angle a surveyor, drone pilot, or observer on a height looks down through to see an object below. Enter the vertical drop between the two points and the horizontal distance between them, and this calculator returns the angle of depression and the direct line-of-sight distance, useful for site surveying, grading checks, and trigonometry problems alike.

How to use the angle of depression calculator

Enter the vertical distance — the height difference between the observer and the object, in your chosen unit.
Enter the horizontal distance — the flat, straight-line distance between the observer's position and the object below.
Read off the angle of depression in degrees, plus the line-of-sight distance (the direct, straight-line distance between the two points).

The angle of depression formula, explained

The angle of depression, vertical drop, and horizontal distance form a right triangle, so angle of depression = arctan(vertical distance / horizontal distance).

Worked example: an observer on a 20 m tower looks down at a point 40 m away horizontally. Angle of depression = arctan(20 / 40) = arctan(0.5) = 26.57 degrees. The line-of-sight distance (the hypotenuse) is 20 / sin(26.57 degrees) = 44.72 m.

The angle of depression from the higher point always equals the angle of elevation measured from the lower point back up to the observer, since the horizontal reference lines are parallel.

Pro tips

Both distances must be measured on the same two reference points and in a straight line — mixing a slope distance in for the "horizontal distance" field will inflate the angle.

The maximum possible angle of depression is 90 degrees, which only occurs when looking straight down (horizontal distance of zero).

A surveyor callout to measure a sightline or depression angle on site in Gibraltar typically costs GBP 190-520 for a one-off measurement visit, depending on access to the site.