Measurements averaging - lz1asl/CaveSurvey GitHub Wiki

CaveSurvey allows different combinations of devices to be used for measurements collection. While the laser distance meters are proven to be accurate within millimeters and the strong gravity allows good inclination readings, this is not the case with the magnetic sensors. Depending on the device and its configuration their performance varies a lot and is rarely stated by the manufacturer. In CaveSurvey we try to mitigate this with:

• Configurable orientation sensor
• Sensor accuracy visualization (as reported by the Android platform)
• Sensors tests screen where you can play and compare with other devices
• Measurements averaging over multiple values (both orientation and inclination)

The latter works the following way:

• You are given a configurable amount of time to steady point to the target station. The current value(s) and accuracy are displayed in real time.
• Once the targeting time is over, either the last or the averaged value can be used depending on the configuration. Usually the value is 'jumping' a bit and the last measurement value might not be the best one.
• You can enable averaging and configure the number of measurements. At the end of the heading time there are already some measurements collected. The average value and standard deviation are computed and displayed (e.g. 123.45 ±0.05 out of 10 values). Next measurements are allowed only if the standard deviation over the collected values is getting lower (more values in the 'same' direction) and replace the oldest ones.
• Once the deviation becomes steady or starts growing, the set of measurements is fixed. The next step is noise filtering. Up to 20% of the values that have the biggest distance from the average are removed.
• The average over the rest of the measurements is calculated again and used as a final value