ADVANCES IN CAVE VOLUME CALCULATIONS: REFINEMENT OF THE COMPASS® SOFTWARE
The most commonly used free software for cave mapping that provides cave volume is Compass ®. Data collected from traditional surveying techniques is input into Compass as left, right, up, down distances and both inclination and azimuth. Based on these parameters Compass creates a three dimensional representation of the cave by combining polygons.
In the summer of 2014 CaveXO (a program within Compass) was publically released with a volume tool that was created to yield more accurate volume calculations than the preexisting Compass software. However, Larson et al. (2013) determined that there were volume accuracy issues with the CaveXO software. Larson et al. attempted to address this by creating idealized cave passages of fixed diameter and length and developed correction factors for each type of cave passage to be applied to the cave volume calculations within Compass.
However, passage diameter does affect the correction factor for different idealized passage shapes (straight, obtuse, right and acute angles); though passage length does not appear to affect the correction factors. Changing the diameters of idealized passages demonstrated that the actual volume of the shape and the volume calculated by CaveXO can vary by up to 900%, though is commonly less, ~50%. These differences in the correction factors also persist regardless of where the idealized survey data was collected (i.e. inside wall, center, and outside wall). The larger the diameter of the passage the larger the error, however, the error is not always linear with increasing passage size. These improved correction factors can be applied to preexisting cave survey data to allow for further refinement and calculation of actual cave volume than was possible before.