28 lines
1.2 KiB
TeX
28 lines
1.2 KiB
TeX
\subsection{Barometer}
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If available, the Smartphone's barometer is used to infer the likeliness of the current $z$-location.
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%
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As ambient pressure readings are highly influenced by environmental conditions
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like the weather, time-of-day and others \cite{Muralidharan14-BPS},
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we use relative pressure instead of absolute ones.
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%
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Due to noisy sensors, more than one reading is used to estimate this relative base.
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The usual setup time of a navigation-system (route calculation, etc.)
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is used to average all barometer readings during this timeframe.
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This average $\overline{\mObsPressure}$ serves as relative base.
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Furthermore, we estimate the sensor's uncertainty $\sigma_\text{baro}$ for later use within the evaluation step.
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During each transition from $\mStateVec_{t-1}$ to $\mStateVec_t$, we need a corresponding, relative
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pressure prediction $\mStatePressure$ which is adjusted whenever a $z$-change happens within the transition.
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%
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% \begin{equation}
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% \mState_{t}^{\mStatePressure} = \mState_{t-1}^{\mStatePressure} + \Delta z \cdot b
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% ,\enskip
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% \Delta z = \mState_{t-1}^{z} - \mState_{t}^z
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% ,\enskip
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% b \in \R
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% \enspace .
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% \label{eq:baroTransition}
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% \end{equation}
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