near to final draft
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@@ -10,8 +10,8 @@
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\label{fig:paths}
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\end{figure}
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%
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The experiments were carried out on all floors (0 to 3) of the faculty building.
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Each floor is about \SI{77}{\meter} x \SI{55}{\meter} in size, with a ceiling height of \SI{3}{\meter}.
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The experiments were carried out on all four floors of the faculty building.
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Each floor is about \SI{77}{\meter} x \SI{55}{\meter} in size, with a ceiling height of about \SI{3.0}{\meter}.
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To resemble real-world conditions, the evaluation took place during an in-house exhibition.
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Thus, many places were crowded and Wi-Fi signals attenuated.
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As can be seen in fig. \ref{fig:paths} we arranged 4 distinct walks, covering different distances, critical sections and uncertain decisions leading to multimodalities.
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@@ -29,7 +29,7 @@ Even though, the error during the following few seconds is expected to be much h
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The measurements were recorded using a Motorola Nexus 6 and a Samsung Galaxy S5.
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As the Galaxy's \docWIFI{} can not be limited to the \SI{2.4}{\giga\hertz} band only, its scans take much longer than those of the Nexus: \SI{3500}{\milli\second} vs. \SI{600}{\milli\second}.
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Additionally, the Galaxy's barometer sensor provides fare more inaccurate and less frequent readings than the Nexus does.
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Additionally, the Galaxy's barometer sensor provides far more inaccurate and less frequent readings than the Nexus does.
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This results in a better localisation using the Nexus smartphone.
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The computation for both filtering and smoothing was done offline using the aforementioned \mbox{CONDENSATION} algorithm and multinomal (cumulative) resampling.
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For each path we deployed 10 MC runs using \SI{2500}{} particles. BS uses $500$ sample realisations drawn with a cumulative frequency.
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@@ -89,8 +89,8 @@ Now, the positional average error along all 4 paths using the Nexus and the Gala
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The BS performs with an average error of \SI{2.21}{\meter} for filtering and \SI{1.51}{\meter} for smoothing.
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The difference between both filtering steps is of course based upon the randomized behaviour of the respective probabilistic models.
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It is interesting to note, that the positional error is very similar for both used smartphones, although the approximation error varies greatly.
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Using the FBS, the Galaxy donates an average approximation error of \SI{4.03}{\meter} by filtering with \SI{7.74}{\meter}.
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In contrast the Nexus 6 filters at \SI{5.11}{\meter} and results in \SI{3.87}{\meter} for smoothing.
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Using the FBS, the Galaxy provides an average approximation error of \SI{4.03}{\meter} while filtering resulted in \SI{7.74}{\meter}.
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In contrast, the Nexus 6 filters with an error of \SI{5.11}{\meter} and \SI{3.87}{\meter} for smoothing.
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The BS has a similar improvement rate.
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@@ -106,7 +106,7 @@ It can be clearly seen, how the smoothing compensates for the faulty detected fl
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Additionally, the initial error is reduced extremely, approximating the pedestrian's starting position down to a few centimetres.
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In the context of reducing the error as far as possible, fig. \ref{fig:int_path2} b) is a very interesting example.
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Here, the filter offers a lower approximation and positional error in regard to the ground truth.
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However it is obvious that smoothing causes the estimation to behave more natural instead of walking the supposed path.
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However it is obvious that smoothing causes the estimation to behave more natural, due to the restrictive smoothing transition, instead of walking the supposed path.
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This phenomena could be observed for both smoothers respectively.
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At next, we discuss the advantages and disadvantages of utilizing FBS and BS as fixed-lag smoother.
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@@ -128,8 +128,8 @@ For better distinction, the path was divided into $10$ individual segments.
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\label{fig:lag_error_path4}
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\end{figure}
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%
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Again it can be observed, that both smoother enable a better overall estimation especially in areas where the user is changing floors (cf. fig. \ref{fig:lag_error_path4} seg. 4, 7).
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Immediately after the first floor change, a long and straight walk down the hallway follows.
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Again it can be observed, that both smoothers enable a better overall estimation especially in areas where the user is changing floors (cf. fig. \ref{fig:lag_error_path4} seg. 4, 7).
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Immediately after the \newline first floor change, a long and straight walk down the hallway follows.
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While the Wi-Fi component pulls the pedestrian into the rooms on the right side, the actual walking route was located on the left side of the floor (see ground truth in fig. \ref{fig:lag_comp_path4} seg. 6).
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Here, the BS is able to slightly improve the path, whereas the FBS follows the filtering until the upcoming staircase provides the necessary information for adjustments.
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%It follows a critical area with high errors and multimodalities.
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@@ -141,7 +141,7 @@ Especially in seg. 8 and 9 a big crowd was gathered and highly attenuated the Wi
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For an excessive amount of time, the absolute location estimated by the Wi-Fi component got stuck in the middle of seg. 8 and therefore delayed the estimation.
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The next viable measurements were then provided at the end of seg. 9.
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This suggests that the here presented smoothing transition is able to improve the estimated path visibly, but does not compensate for those jumps in a timely manner.
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Finally, the BS provides an approximation error alongside all paths of $\SI{6.48}{\meter}$ for the Galaxy and $\SI{4.47}{\meter}$ for the Nexus by filtering with $\SI{7.92}{\meter}$ and $\SI{5.50}{\meter}$ respectively.
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Finally, the BS provides an approximation error alongside all paths of $\SI{6.48}{\meter}$ for the Galaxy and $\SI{4.47}{\meter}$ for the Nexus, while filtering resulted in $\SI{7.92}{\meter}$ and $\SI{5.50}{\meter}$ respectively.
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Whereas FBS improves the Galaxy's estimation from $\SI{7.73}{\meter}$ to $\SI{6.68}{\meter}$ and from $\SI{5.66}{\meter}$ to $\SI{4.80}{\meter}$ for the Nexus.
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As stated before, the main advantage of BS over FBS is the better computational time by just using a sub-set of particles for calculations.
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