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@@ -10,12 +10,12 @@
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and ignoring the shortest-path suggested by the system.
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Due to an in-house exhibition during that time, many places were crowded and \docWIFI{} signals
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are attenuated.
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To enable error calculation, each acquired path is backed by ground truth information.
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% To enable error calculation, each acquired path is backed by ground truth information.
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The ground truth is measured by recording a timestamp at marked spots on the walking route.
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While walking, the pedestrian clicked a button on the smartphone application
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when passing a marker. Between two consecutive points, a constant movement speed is assumed.
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Thus, the ground truth might not be \SI{100}{\percent} accurate, but fair enough for
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error measurements. All walks were performed using a Motorola Nexus 6 and a Samsung Galaxy S5.
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Thus, the ground truth might not be \SI{100}{\percent} accurate, but fair enough for error measurements.
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All walks were performed using a Motorola Nexus 6 and a Samsung Galaxy S5.
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As the Samsung Galaxy S5's \docWIFI{} can not be limited to the \SI{2.4}{\giga\hertz} band only,
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its scans take much longer than those of the Motorola Nexus 6:
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@@ -53,15 +53,11 @@
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%
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The following evaluations will depict the improvements that the prior path knowledge is able to provide,
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even when other system parameters are badly chosen.
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Just adding importance-factors (described in \ref{sec:wallAvoidance} and \ref{sec:doorDetection})
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to the simple transition \refeq{eq:transSimple} addresses only minor local errors
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The following evaluations will depict the improvements that the prior path knowledge is able to provide, even when other system parameters are badly chosen.
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Just adding importance-factors (described in \ref{sec:wallAvoidance} and \ref{sec:doorDetection}) to the simple transition \refeq{eq:transSimple} addresses only minor local errors
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% like not sticking too close to walls. In most cases this lead only to slight improvements
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and is therefore not further evaluated.
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To examine the contribution our approach is able to provide, we will have a closer look
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at a long walk with many stairs, intentionally leaving the shortest path several times,
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named path 4 (see fig. \ref{fig:paths}).
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To examine the contribution our approach is able to provide, we will have a closer look at a long walk with many stairs, intentionally leaving the shortest path several times, named path 4 (see fig. \ref{fig:paths}).
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%
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% all paths we evaluated
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\begin{figure}
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@@ -107,7 +103,7 @@
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This can be seen at the red area in the upper left corner of fig. \ref{fig:nexusPathDetails} \refSeg{1} and within
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segment \refSeg{1} of fig. \ref{fig:errorTimedNexus}.
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%
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Starting with both, known position and heading, reduced the error by about \SI{15}{\percent} when using prior knowledge and
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Starting instead with both, known position and heading, reduced the error by about \SI{15}{\percent} when using prior knowledge and
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by \SI{25}{\percent} when omitting prior knowledge. As prior knowledge directs the density towards a known target,
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it is able to compensate unknown initial headings which explains the \SI{10}{\percent} difference.
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%
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@@ -127,8 +123,8 @@
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the density from being dragged into the office-rooms, the estimated path is still located on the wrong side
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of the hallway. As both sides of the floor result in a route with almost the same length,
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just knowing the pedestrian's destination is not able to provide further improvements.
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Thus, a constant error of approximately the floor's width remains.
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This is clearly visible in fig. \ref{fig:nexusPathDetails} \refSeg{6}.
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Thus, a constant error of approximately the floor's width remains
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as seen in fig. \ref{fig:nexusPathDetails} \refSeg{6}.
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%
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Due to the excellent barometer installed within the Nexus 6, changing the floor provides only small estimation
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errors in segment \refSeg{7}.
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@@ -136,7 +132,7 @@
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Due to an in-house exhibition during the time of recording, we had to leave the ground truth by a few meters.
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Furthermore, the overcrowded areas lead to attenuated \docWIFI{} signals. Both reasons move the
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density into another stairwell (see fig. \ref{fig:nexusPathDetails}, red lines in the lower right).
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The resulting multimodality (two staircases possible at the same time) leads to a rising error
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The resulting multimodality (two staircases possible) leads to a rising error
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\refSeg{8}, \refSeg{9}. At the end of the walk \refSeg{10} the system is able to recover, again.
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@@ -154,11 +150,11 @@
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% \caption{Nicht so markant beim galaxy, denke aber der platz reicht eh nicht, also einfach kurz erwaehnen}
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%\end{figure}
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The median error values for all other paths and the other smartphone are listed in table
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\ref{tbl:errNexus}. Furthermore, fig. \ref{fig:errorDistNexus}
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The median errors for all conducted walks are listed in table \ref{tbl:errNexus}. Furthermore, fig. \ref{fig:errorDistNexus}
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depicts the error development for several percentile values. As can be seen, adding prior
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knowledge is able to improve the localisation for all examined situations, even when
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knowledge improves the localisation for all examined situations, even when
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leaving the suggested path or when facing bad/slow sensor readings.
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\newpage
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%\commentByFrank{fig. \ref{fig:errorDistNexus} erwaehnt}
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% error values
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@@ -257,9 +257,7 @@
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\newcommand{\pathRef}{v_\text{ref}}
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%
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Before every transition, the centre-position $\pathCentroid = \fPos{\mStateVec_{t-1}^*}$ of the current sample-set, where
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\begin{equation}
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\mStateVec_{t-1}^* = \underset{\mStateVec_{t-1}}{\argmax} \enspace p(\mStateVec_{t-1} | \mObsVec_{t-1})
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\end{equation}
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$\mStateVec_{t-1}^* = \argmax_{\mStateVec_{t-1}} \enspace p(\mStateVec_{t-1} \mid \mObsVec_{t-1})$
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represents the most proper state of the posterior distribution at time $t-1$, is calculated.
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%
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%
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