GPS routing

Discussion in 'Gen 2 Prius Audio and Electronics' started by qbee42, Feb 3, 2012.

  1. qbee42

    qbee42 My other car is a boat

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    Over the years we have had a lot of discussions about Nav systems and why they do what they do. The Prius Nav system takes its share of deserved abuse, but today I was driving my Jeep and using a Garmin Nuvi for navigation. I made a round trip to a location and then straight back. The Garmin took me on two different routes, even though it was a reciprocal trip.

    All of the roads were two-lane country roads, without one-way streets or other reasons to show directional preference. It just goes to show that Nav routing is not entirely deterministic, at least from the perspective of the common user.

    Tom
     
  2. Hal W

    Hal W New Member

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    You may have it set on the eco. mode? It takes into account alt. and all kinds of strange things. You can set it for shortest route, fastest time and or economy! Hal
     
  3. rkalbo

    rkalbo Junior Member

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    I have my garmin set for my work location and some how it changed to a few 100 feet up the road
     
  4. qbee42

    qbee42 My other car is a boat

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    Same mode both ways. I suppose it might prefer the grades one way over the other, but the first route was so full of stops and turns it's hard to imagine that way being economical.

    Tom
     
  5. fuzzy1

    fuzzy1 Senior Member

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    I don't know what time resolution it uses when deciding between route choices, but another mapping application on my PC does produce anomalies when two choices are essentially tied.

    Also, if an application such as Garmin has a sense of vehicle direction and is looking for a safe U-turn location, the time it allots for turning around could easily exceed the computed time difference between two nearly matched routes. And vehicle direction might be established by nothing more than GPS noise, especially immediately after powerup while still parked..

    At least one online mapping application (don't remember which) makes it easy to view a few alternate routes when there are drastically different choices with nearly identical travel times. I wish Garmin did the same.
     
  6. Hal W

    Hal W New Member

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    If it is set for best economy it will take the most economical route. Most run with fastest route. You have to go into set-up and check it out. It can be set to other things like tole bridges [Yes or No] Tole roads[Yes or No] Hal
     
  7. fuzzy1

    fuzzy1 Senior Member

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    The Economy setting on my Garmin is essentially worthless, especially in a Prius with nearly identical Highway and City MPG ratings. It knows only those two MPG figures entered by the user, and must have roads internally flagged as one or the other. It knows nothing about terrain or stop signs or any other factors influencing fuel consumption.
     
  8. Hal W

    Hal W New Member

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    My 1490 seems to take into account altitude! Mind you I haven't played with it much. I normally set up for the fastest time unless I have lots of time then I go for shortest distance. Mine will also take you around traffic jams when they are on your track! Hal
     
  9. fuzzy1

    fuzzy1 Senior Member

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    While my 755 knows current altitude, its City Navigator North Anerica map lacks altitude on its dababase, so it doesn't know elevation profiles on the route ahead.

    My hiking GPS with Garmin's Topo U.S. map does have altitudes in its dabase, but it doesn't do my driving routes.
     
  10. jpadc

    jpadc Type before I think too often

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    I've seen my Garmin do that for most every trip for which I've used it both coming and going to a location. It seems as if it calculates a route from the start point and plots from that point to the nearest "major road" that heads in the right direction and then figures out the rest from there.

    One funny example is the routes it calculates from my house in Indy to IKEA in Cincinnati (West Chester, OH technically) and back. The routes are indeed so different it has me getting off I275 and using surface streets to get there but has me get back on I75 and take it to I275 to get back home. I don't go that way going back, but Garmin calculates it that way. The Prius Nav wants me to use the I75 exit both coming and going but its data is so old it does not know IKEA exits :)

    I assume they all have proprietary route calculation routines and as such they all have odd quarks to them.
     
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