Triangulation also uses triangles, but this time it uses one distance and two angles to work out the location of the object or feature, rather than the three distances used in trilateration. This can be useful if there are obstacles in the way, or the distances are very long for measuring. It is also useful for measuring the height of something, for example how tall a tree is, or how high the height of the house.

Triangulation process:

1. The process starts the same as trilateration; measure and plot points A and B. These can be any two fixed points that you already know the location of, in this case topiary (A) and a statue (B).

Amber Crowley / public domain

2. Set up a theodolite or dumpy level at point A and look through it to point B, set this as 0 degrees.

3. Swivel the theodolite or dumpy level until you ae looking at point C (in this example, a tree) and record how many degrees it is.

4. Move the theodolite or dumpy level to point B and set it up so that when you are looking at point A it reads 0°. Then swing round and measure the degrees from B to C.

5. On your paper draw a line between A and B and then use a protractor to measure the angles of 40° from point A and 65° from point B. Draw lines from point A and B in the correct direction of each angle until the lines cross. Where they cross is point C: