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Level 5 Edit: M60 Barton Bridge, Manchester.

Post by andrewinlancashire
Hello.
The motorway here seems quite a way off the satellite imagery and GPS points. Is there any way this could be an issue?

Regards
Andrew
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Post by andrewinlancashire
Thanks Ian. I've thought about the accuracy of the Google images and the GPS points before. I would generally tend to trust the images over the GPS points. I have in the past compared the images from Google Maps/Earth with coords obtained from survey grade GNSS receivers (cm accuracy) and the image accuracy has been surprisingly good - within a few metres.

Obviously you're aware of multipath errors with your comment of reflections. This is something that could affect all GNSS receivers and may lead to a whole stream of GPS points being way off, but if that was the case then I suppose you could argue that the road may be best mapped out of position to stay close to the users GPS location. I digress...

I suppose my concern with that location you've fixed would be with route calculation. If a user was sitting in traffic searching for a new route and they were on an area of map that was out of line with the GPS position, as Waze calculates a new route, is there anything to stop the app from thinking it's on the other side of the motorway heading in the opposite direction?

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Andrew
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Post by andrewinlancashire
Ah! Thanks for the explanation.
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Post by ditchi56
Waze has a very considerable tolerance, to allow for low quality phone GPS traces, reflections bouncing of buildings, and indeed roads being several lanes wide. So it shouldn't be an issue.

Nevertheless, I've realigned the motorway mapping to better fit reality.

Be warned that Google sometimes get their aerials out of line, in which case we wouldn't want to mirror them exactly. That doesn't seem to be the case here though, since the GPS traces match the aerials.

Ian
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Post by ditchi56
PastaFasta wrote:If a user was sitting in traffic searching for a new route and they were on an area of map that was out of line with the GPS position, as Waze calculates a new route, is there anything to stop the app from thinking it's on the other side of the motorway heading in the opposite direction?
If you shut the app down completely and then reopened it you may perhaps get this problem.

Otherwise it seems pretty good at remembering where it is placed on it's map and which way it is facing. Indeed, this memory is a problem in other circumstances. If your destination is a street address, when you come to start a new journey, Waze will assume you cannot turn around and start you off facing in the same way. This can lead to an unnecessary detour if your new journey is back where you came from.

This is one reason for mapping "parking road"s, once Waze has turned into a car park or similar to reach the destination, it will start the new journey with a turn out of the car park, which can presumably be in either direction. (Note that mapping a car park point or area is not key for this, it's getting the destination navigation point onto a road which gives Waze what it regards as an acceptable way of turning that matters.)
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