Loop Closure Loop Closure Loops. Many caves have passages that wind around in a circle and connect back to themselves. When a survey connects back to itself, it called a loop. If a loop is surveyed perfectly, the survey should come back to the exact point at which it started. If the loop doesn't come back to the exact starting point it is called a closure error.
Closure errors indicate that some or all of the survey measurements within a loop have errors.
If the closure errors are large enough, the shape of the loop and the shape of the cave will be distorted by the errors. For this reason, cave survey programs must have a way of dealing with the effects of these errors. Closing loops is a mathematical process that systematically spreads the errors around the cave to minimize the effect of the error on any one shot. In effect, it gives you lots of little errors instead of one big error at the point where the loops close. In this way, there is only minimal distortion of the passages.