loop closure

A process for determining the amount of error in a set of observations within a network. A loop closure is calculated by selecting a point from which one or more observations were taken, adding one of those observations to the point's coordinates, and calculating coordinates of the second point based on that observation. This process is repeated one or more times around a loop, finally ending at the original starting point. If there were no errors in the observations, the final calculated coordinate would be exactly the same as the original starting coordinate.

By subtracting the calculated coordinate from the original coordinate a misclosure is determined. Dividing this error by the length of the line allows the error to be expressed in parts per million. This technique can also be used between two different points when both points are known with a high degree of accuracy. This is also known as a traverse closure.