It is important to note that closing loops does not fix errors in the survey. Loop closure does not locate the source of the errors, or attempt to correct them, it merely distributes the error. The errors in a survey may be either random errors, or systematic errors, or blunders. For small random errors, and small systematic errors, closing loops does tend to make the survey a little more accurate, but this is not always true. If the survey contains blunders (the outright mistakes that most surveys have), closing loops will not make these errors go away, it merely smooths-over the errors by distributing them.
How CavePlot Closes Loops
CavePlot currently closes loops using a best-first sequential method. First, CavePlot locates all the loops, and calculates their closure error. Next, these loops are sorted (best first, worst last) according to an approximation of their statistical "badness". Next the loops are closed and locked, one at a time (again best first).
Closing each loop is done by adjusting each shot within a loop to accommodate a fraction of the total error found to occur in the loop. Error distribution per shot is weighted according to the distance for each shot, relative to the total loop distance.
Finally, after adjusting all the loop survey shots, the entire survey is re-linked to generate new X, Y, and Z positions for each station.
