# S-PDR: SBAUPT-Based Pedestrian Dead Reckoning Algorithm for Free-Moving Handheld Devices
## 5 Results and Discussion
### Indoor Test  
The trajectory for this test set was planned indoor on the second floor of the Engineering ENG building at the University of Calgary. The trajectory was planned to make a full loop around a block of classes to test the Azimuth estimation as the corridors are perpendicular which would make azimuth errors clear. The trajectory passes by multiple metal structures and has high magnetic interference. A sample of the results from S-PDR and Xsens for the planned trajectory is shown in Figure 21. The trajectory is approximately 293 m long and on average took 420 steps to cover with an average step length of approximately 0.7 m for regular walking, and 370 steps with an average step length of approximately 0.8 for fast walking. As shown in the figure, the S-PDR provides a good solution in comparison to the trajectory constructed using the attitudes provided by the Xsens. The trajectory constructed from the Xsens data uses its on-board computed attitudes to transform the on-board gravity compensated linear accelerations to LLF, which is then used for step detection, step heading estimation using PCA, and step length estimation to compute a PDR trajectory solution based on [37]. The Xsens attitudes suffered from high and quick drift because of magnetic interference from the surrounding environment, which leads to higher positional error. The results from the shown indoor test sample show a final positional error of 6.3 m for the S-PDR, while the Xsens trajectory had a positional error of 34.8 m. The test was carried out 20 times using the Samsung S8 phone with the Xsens attached to its back as per the configuration shown in Figure 18. The results for the 20 tests are shown in Table 2. Where the final positional error is the difference between the true position of the end point of the trajectory and the estimated end position. The average position error across the trajectory is the average error at different stages of the trajectory based on land markers and targets with known locations across the trajectory. Figure 21: ENG building reference trajectory and reconstructed trajectory using S-PDR and Xsens. The table shows that S-PDR outperforms the Xsens PDR solution. For the sake of comparison, the trajectories recreated using S-PDR and the Xsens data used the same estimated step length, this way the final error difference between the two systems will be representative of the errors in attitude and headings combined. The results show that the Xsens solution has high variability which is a result of the magnetic interference and instability. The tests were carried out on different days and at different times of the day so that the magnetic print of the place would change, and as shown it highly affects the results of the Xsens. On the other hand, the results for the S-PDR are consistent with low variation under the different surrounding environmental conditions and changes. The average final position error of the S-PDR was found to be much lower and more consistent than the Xsens, and the average position error through trajectory was also much lower than the Xsens as the S-PDR was able to track the trajectory with lower error for most of the trajectory. The analysis of the results presented in Table 2 is shown as boxplots in Figure 22, where each box represents the one sigma confidence interval, the red line inside the box represents the median value, the upper and lower limits represent the maximum and minimum values respectively, and the plus sign represents outliers in the data.