A theodolite is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building and infrastructure construction, and some specialized applications like star or sun observations to determine latitude and longitude which is a method to determine your position on earth that pre-dates modern technologies like the Global Positioning System (GPS).
It consists of a moveable telescope mounted so it can rotate around horizontal and vertical axes and provide angular readouts. These indicate the orientation of the telescope and are used to relate the first point sighted through the telescope to subsequent sightings of other points from the same theodolite position. These angles can be measured with accuracies down to microradians or seconds of arc. From these readings a map can be drawn, or objects can be positioned in accordance with an existing plan. The modern theodolite has evolved into what is known as a total station where angles and distances are measured electronically and stored to be transferred into a desktop computer for further manipulation of the data. Technology advancements now allow data to be captured and then electronically transferred to the office live and in real time.