My Go 720 is not accurate

Discussion in 'General TomTom Discussion' started by georges99, Sep 1, 2007.

  1. georges99

    georges99

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    hi,

    I have a go 720, and it is not accurate. Destination point are about 600 feet further than what the gps is showing. So all the POI are not accurate either, many times, am pass a gas station, and the gps is still showing the number of feet before arriving, and am past 600 to 700 feet when it says that I have arrive.

    beside that, I love the unit.

    George
     
    georges99, Sep 1, 2007
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  2. georges99

    digital-flex

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    If you find the POI off, try and correct the placement as it would benefit all.
     
    digital-flex, Sep 1, 2007
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  3. georges99

    tundra914

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    Its not the unit, but the mapping software. My Garmin nuvi 360 does the exact same thing, it tells me walmart and circuit city are on top of a over pass in maryland. :eek:
     
    tundra914, Sep 1, 2007
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  4. georges99

    chantililace

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    i have the same problem with my destinations. They are around 200 feet off. What is the deal here? The Garmin Navtec put me bang on AND even said if the destination was on the left or right.

    Is this a hardware problem or a map problem?



     
    chantililace, Sep 11, 2007
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  5. georges99

    digital-flex

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    I would bet that it is a map problem. I would report the problem to TT or Tele Atlas of the problem.
     
    digital-flex, Sep 11, 2007
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  6. georges99

    MiniforEB

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    Location:
    Round Hill, VA
    TomTom Model(s):
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    Could it also be a drift issue?

    I have seen some posts on the 720, where it seems to have a small problem with "drift" or having difficulty getting a good satellite fix. I don't recall seeing anything here about whether the unit was still moving when it indicated that "arrival" had occurred.

    Either way, if in fact the 720 was no longer in motion, then I would report the error to TeleAtlas.
     
    MiniforEB, Sep 11, 2007
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  7. georges99

    ptco911

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    Location:
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    So far my issues have been map related. There are points of driving cross country (at least according to the 720) when I am on a road that has been in place for quite some time. There are a few that are new sub divisions and that is understandable. I am going to Kansas City this weekend and will try it in both the downtown and the suburbs to see how it performs.
     
    ptco911, Sep 11, 2007
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  8. georges99

    lec510

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    When it says "Arrive at your destination" it doesn't mean that's your destination.
    Look at the distance count down, until the flag disappears that where it is. You count the error from that moment on, not before & not after.
    Don't expect it to be miracle figure.
    People using Handheld GPS (which are much more accurate) for geocaching expect them to lead right to the caches are in the same boat as you're. I say 20' error for a handheld, 50' for a car are pretty good figure.
    Also they don't measure coordinates of every houses on a street, they do it in blocks. If you want accuracy, then do it yourself.
     
    lec510, Sep 12, 2007
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  9. georges99

    The Spook

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    I think the problem here, and with other "My GPS isn't accurate!" complaints, is probably related to house number ranges. The map doesn't contain every single house number, only number ranges. The voice instructions tell you that your destination is reached when you enter this range.

    For example, if I 'navigate to..' 15 Whatever Street, Anytown, USA and the map data only contains the range 10-20. You will hear the destination reached message when you reach either 10 or 20 (depending which direction you arrive from), even though you have a little way to go to get to number 15.
    [sarcasm]This is where the trusty Mk.1 Human Eyeball (in combination with Brain 1.0) comes into play![/sarcasm]

    If you tap on street location in the map view, you will see the house number range.

    Personally, I don't think it is a map error that all numbers are not included. I should imagine that they are not because of space limitations. Storing every single house number would presumably use a lot of space and brings no great advantages. Afterall, providing you have both Eyeball and Brain, you should be able to find number 15 from your current position at number 20.

    GPS systems are an aid to navigation, not a complete autopilot system (or replacement for the aforementioned features of most humans). Does a paper map show every house number?
     
    The Spook, Sep 12, 2007
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  10. georges99

    chantililace

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    Great, let us know. All my suburb locations are usually 200-300 feet off !! Driving on the roads is accurate as it shows me under an underpass when I am actually there....so this is map related, not a GPS or hardware problem..?.
     
    chantililace, Sep 13, 2007
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  11. georges99

    chantililace

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    I understand what your are saying, but my destination is 2-300 feet off wher the tomtom has placed the checkered flag, which is quite a distance to use your eyeball if it is an unfamiliar area. What I am getting at is that the Navetech/Garmin map is bang on most of the time with the checkered flag location of a particular address, whereas the tomtom is off (2-300 feet) as mentioned earlier. I don't think it is a GPS or hardware issue, but I can't be positive. The good thing is that is is spot on when dricing down roads on the map shwoing you are under and underpass when you really are.
     
    chantililace, Sep 13, 2007
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  12. georges99

    briand

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    ...further to what The Spook wrote, you need to keep in mind that the maps do not have a [GPS location<>Physical Address] database. The algorithm that determines the 'position' of a given address within your GPS (or any other electronic mapping program) will usually just evenly distribute the address range over the length of road segment pertaining to that range. This does not mean that each property owner on that road segment owns the same exact amount of road frontage!
     
    briand, Sep 13, 2007
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  13. georges99

    lec510

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    Chantililace.
    You seem not to understand that when the flag appears, you don't arrive yet, only when the distance countdown hit 0, and then the flag disappear then you do.
    Lot of people, new to TomTom, don't understand and don't use the Navigation Arrow with the distance bellow that. That's where all essence of TomTom navigation is about. It tell you where (how far), the next move is : Turn left, Right, bear left, right, roundabout, arriving ... at what distance that will happen.
     
    lec510, Sep 14, 2007
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  14. georges99

    bilybob

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    This was mentioned on GPS mag (tomtom hater) site, the only drift I have ever noticed is if you are off the road which I think is not really drift, it is just trying to snap to the closest road.

    I thought tomtom was not accurate either when I first got it compared to my old garmin, so I created a few POIs using mapsource to test the accuracy. The POI's on tomtom unit are actually closer to the destination most of the time. I think the problem is in the routing logic. Garmin announces arriving at destination on left or right when it is a couple of hundred feet away and then just snaps you to the end of the route. Tomtom says in 200 feet you have reached your destination with the arrow pointing in the direction, and then waits for you to finish those 200 feet before announcing you have reached your destination. Which way you prefer is just a personal preference.
     
    bilybob, Sep 14, 2007
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  15. georges99

    chantililace

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    Guys,

    I understand how to use a GPS. I know about this distance counter. I can put in a POI or an exact address. It says arriving at destination. I know the destination is directly right beside my car, however it is still telling me that I am 65 meters (give or take depending on address) from my destination. I am right beside my destination! If I move to where the flag/distance counter hits zero I am at the end of the block! This is true for many of my POI's and addresses I select. If I was trying to find something at night and I worked off the distance counter and flag, I would be left going driving around the block squinting at the house signs. The Tomtom likes to say arriving at destination as soon as you turn onto the block which is fine, but I am working off the flag and distance counter to home in. The Garmin is more accurate with their map and also tells you if the location is on your left or right. I have even put them side by side and there is no comparison to the accuracy of the Garmin map. I will fool around with it some more but this is the results I am getting. This is my only complaint now that I have a correct working bluetooth unit.

    If I am missing something big here, please let me know. Thanks.
     
    chantililace, Sep 14, 2007
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  16. georges99

    lec510

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    The POI are they made by you, by the others, or by TomTom ?
    Try this: in front of your home with the GPS, let it acquire full signal, set your Home as current GPS position, drive away away a few blocks then Navigate Home.
    If you find the error is more then 50' then go & buy a Garmin.
    This is a TomTom forum, nobody wants to hear you praising the virtue of Garmin.
    For one of TomTom headaches, I can cite 10 from Garmin.
    ** NOTE: lot of people here were ex Garmin users (like Pedro).
     
    lec510, Sep 14, 2007
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  17. georges99

    briand

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    I think the point (made by both The Spook and myself), is what you missed.

    There is no GPS Coordinate <--> Physical Address mapping.

    If you select a navigation point by address, your GPS unit will approximate the location of that address, based on the address range saved with the definition for that road segment. The algorithm used to determine what spot on the map to point at for a given address may very well differ between different GPS units (and, perhaps, moreso between different brands of GPS units!).

    You've stated that your old Garmin unit would even tell you which side of the street a given address was on -- this is solely because they've programmed this into the address location algorithm in their units. It is not, however, correct (or, for that matter, without flaw). Garmin makes the assumption that all even number addresses are on one side of the road, and all odd number addresses are on the opposite side of the road (as this is customary in the US; It is not, however, a hard and fast rule!). My old Garmin unit would consistently tell me that my eye doctor was on the east side of the road (along with all the other odd-numbered addresses), when in fact it is on the west side of the road! (2727 Capital Circle NE, Tallahassee, FL 32308) It's wrong, because the assumption made by the programmers who created Garmin's algorithms is invalid. Odd number addresses don't always show up on the eastern side of north/south running roads, nor does it follow that if one address on the left side of the road is even, that all addresses on that side of the road are also even. It may well be true most of the time, but it's not true all of the time.

    For this reason, you will not get exact address placement on a GPS map, at any time. It will always be an approximation, perhaps valid, perhaps not. The only address information stored in the map definition for any given road segment is an address range. It is not possible, on any GPS unit, to place a specific address accurately on a road given the limitations of the data available. A specific address may be calculated, however, and that calculation may be "close", "close enough", "spot on!", "way the heck off!" (or anywhere in between) in reference to the actual physical location of that specific address.

    - Brian
    (...who knows a thing or two about GIS...)
     
    briand, Sep 14, 2007
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  18. georges99

    lec510

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    Brian,
    I think the guy is a troll.
     
    lec510, Sep 14, 2007
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  19. georges99

    briand

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    yeah, you may be right. ...but we don't need any newbies scanning through this thread and thinking that the "address locations" are "bad" in TomTom units, either... ;)
     
    briand, Sep 15, 2007
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  20. georges99

    chantililace

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    Sorry guys, I am not a troll, just a newbie asking questions and starting a good debate.

    Thanks for your replies.
     
    chantililace, Sep 15, 2007
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