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GPS-route testing

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Introduction Goal is to introduce the results of

GPS-route accuracy tests Discuss about the problems

encountered while testing GPS-receivers

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Contents What effects GPS-signal accuracy Tested GPS-receivers Test setting Encountered problems Test results

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Uncontrollable variables Satellite coverage Weather Obstacles in route (roadworks,

traffic lights, etc.)

Although uncontrollable, these can be taken into account when planning testing

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Controllable variables Devices Route Device position Location refresh rate (8s. intervals) Travelling method & speed

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Test setting 8 tested devices

5 mobile phones using internal receiver

2 external Bluetooth receivers 1 wrist GPS

Clear weather

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Test route

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Possible problems Synchronizing Separating sequentially recorded

routes from each others Acquiring accurate reference route

& map anomalies Battery charge Data transfer (contracts & costs)

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Measuring error to reference Different ways to calculate

distance between routes The DP-algorithm used:

for each actual point count distance to each of the remaining reference points pick smallest sum to optimal distance so far

Divide optimal sum with number of actual points within route

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Problems with algorithm

Given results are better than what’s the actual error

This is due to comparing actual points to closest points in the reference route

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Assumptions and results N95 slider-state might effect accuracy External receivers are expected to

produce better results Wrist GPS is expected to provide better

accuracy than integrated mobile phone receivers

Every device produced accuracy of less than 10 meters

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Ranking of tested devices 6110 2.73m N95-2, open 3.13m N95-1 w/ external (Pretec) 3.61m Garmin wrist-GPS (1s.) 3.69m Garmin wrist-GPS (8s.) 3.75m E72 3.76m E66 5.10m N95-2, closed 6.05m N95-2 w/ external (Fortuna) 6.44m

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Example of actual routes (external)

Pretec

Fortuna

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Another example

Fortuna

Pretec

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Further improvements Implementing different kind of

measurement algorithm Creating better reference route