Uncertainty Settings

This option allows you to set the uncertainty of instruments. Both the Compiler and the Loop Closer use these options.

Loop Closer. The Loop Closer uses the uncertainty settings when the program uses the Standard Deviation Mode of loop closure. When the program is using Standard Deviation Mode, it makes certain assumptions about how accurately a compass, inclinometer, or tape measure can be read. These assumptions allow the program to make predictions about the size of error to expect in any particular loop. Since there is some variation in the quality, accuracy, and stability of instruments and surveyors, the program allows you to change the assumption used.

Compiler. The Compiler uses the uncertainty settings to find blunders. The uncertainty settings allow the Compiler to predict loop errors and thus determine which loops have blunders in them.

There are three values that you can change: Length Uncertainty, Azimuth Uncertainty, and Inclination Uncertainty.

1. Length Uncertainty. This is a measure of how accurately and consistently you can read a tape measure. The current default value is .1 foot (.03m.). This means that the program assumes that the average error when reading the tape measure will be .1 foot. It should take into account all factors that affect the quality of readings. In a tape measure, things like humidity, temperature, tension, stretch, etc. affect the accuracy.

2. Azimuth Uncertainty. This is a measure of how accurately and consistently you can read a compass. The current default value is two degrees. This means that the program assumes that the average error when reading the compass will be about two degrees. It should take into account all factors that affect the quality of readings. In a compass, things like steadiness of hand, quality of the instrument, magnetic disturbances, parallax, inclination angle, etc. affect the accuracy.

3. Inclination Uncertainty. This is a measure of how accurately and consistently you can read an inclinometer. The current default value is two degrees. This means that the program assumes that the average error when reading the inclinometer will be about two degrees. It should take into account all factors that affect the quality of readings. Inclinometer readings are affected by things like quality of the instrument, parallax, eyesight of the surveyor etc.

Different instruments have different accuracies. For example, experiments on a test survey course show that tripod mounted Bruntons are most accurate, followed by Suuntos and then Sustecos. Also, due to variations in the manufacturing process, there will be variations in quality even with instruments of the same brand name.

It is difficult to give exact numbers about what level of uncertainty you should expect. There are so many factors that affect accuracy, including the type of cave and experience of the surveyor. For example, it is much easier to make accurate readings in a big warm cave like Lechuguilla, than in a cold, wet, crawly cave like Groaning. One way to deal with this issue is set up a test survey course in or near the cave you are working on. This way you can periodically check the accuracy of your instruments and surveyors.