Fig. 4

Results of the cross-validation analysis. Cross-validation errors (mean ± 2 s.e.m.) are shown as function of the number of satellites of the validation set (i.e. the out-of-set Fastloc-GPS data) for analyses where (left) single positions were omitted (10 % of data) and (right) series of five consecutive positions were omitted (50 % of data). Positional cross-validation errors were calculated for five different track types: 1) a track with linear interpolation between visual position fixes (♦), 2) a track with linear interpolation between Fastloc-GPS position fixes (×), ‘forced-point’ dead-reckoning tracks initially calculated with 3) constant speed (■) or 4) speed from flow noise (▼), and 5) the mean posterior track of the Bayesian state-space model (●). One-dimensional positional errors for Fastloc-GPS derived from the large data set collected during dry tests (▲) are shown for comparison (see also Additional file 6: Figure S16). Symbol horizontal positions have been offset for clarity