TT One LE - on screen route updates truly 'real time'?

Discussion in 'Maps and Routing' started by Probedude, Dec 5, 2007.

  1. Probedude

    Probedude

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    So this week I've been putting my LE through its paces. I have a 100 mile round trip daily commute that is pretty much all freeway.

    Because of traffic I frequently get off the freeway to bypass a slow/stopped section and then pop back on later - sometimes as soon as the same onramp (half mile offramps and half mile onramps can bypass a lot of traffic.)

    What I've noticed is that though I have left the freeway, and am decently far from it (hundreds upon hundreds of feet from the freeway) my LE will still have me traveling on the freeway for 5-8 seconds if not longer. Almost like it is assuming I am still on the freeway - even updating the progress on the freeway, while it is doing something in the background (just guessing here). After a bit my position will jump to the new road I'm on and it will recalculate my route.

    In one of my bypasses last night, my position wasn't updated until I was already through the offramp intersection, driving away from the freeway direction and already on the 'further down the road' freeway onramp (this is on a long curved part of the fwy). If I didn't know where I was going I would have missed that onramp.

    So, even though I have 6-7 satellite reception, AND my route is updating every second I don't get the feeling that the display and the computations are real time but just give the impression of being real time.

    Anyone have similar experiences?

    Dave
     
    Probedude, Dec 5, 2007
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  2. Probedude

    itguy05

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    It's people like you that cause accidents. Also, it's people like you that should be ticketed as that behavior is illegal in most states (as is passing on the shoulder)

    It's because the GPS "smooths" and averages your position. Most calculate your position numerous times in a second. However, the calculations can vary quite a bit (I've had my Garmin handheld jump all over the place sitting on my desk) depending on the data the unit chooses. You wouldn't want your GPS showing you on the left side, right side, other side, etc so they make an assumption that you are following the road until some # of data points indicate you are off the road. Then the assumption is that you are on the other road. They won't show you "off road" until many data points are showing up off road.

    Also, the accuracy of the maps at these zoom levels may not be the greatest. With my Garmin zoomed at the highest level (20 ft), I can be standing smack in the middle of a road, yet on the map I'm well off the road (with accuracy of <10 ft). I'm sure the highly compressed maps on the GPS units are also not that accurate, so they use some sort of "snap to road" algorithm.
     
    itguy05, Dec 6, 2007
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  3. Probedude

    Probedude

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    Thank you Mr. CHP. Since when does exiting a freeway, coming to a stop sign or traffic light, then get back onto the freeway using the onramp illegal?
    Or are you thinking of clover leafs? This isn't what I meant by "same offramp/onramp", I meant that by "take the MainSt. offramp, stop at the top of the bridge, then take the MainSt. onramp."

    And I don't drive on the shoulder.

    Thanks for the other info. I do find my TT jumping around when sitting stationary on my desk also. My 3 year old Garmin Etrex is rock solid on positioning. It even shows my lane changes when I dump the route to my PC later.

    Dave
     
    Last edited: Dec 6, 2007
    Probedude, Dec 6, 2007
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  4. Probedude

    itguy05

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    I apologize. Around here we have some of those very long on/off ramps for the heavy 18 wheeler traffic. I've seen people "get off" the exit and then at the very last second merge right back into traffic. (that sort of stuff is a pet peeve of mine) Getting off properly and back on is not an issue.

    The amount of detail the Garmin hiking GPS's capture is amazing - it can see me walking around in the house going from room to room. On the trail or geocahing, it's just what you need - quick updates that are accurate to 10-20 feet. However, driving down the road, you can get by with fewer updates.
     
    itguy05, Dec 6, 2007
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  5. Probedude

    sparky672

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    Personally I believe there's a built-in "snap-to-road" function. From what I've seen, it's something like 25 or 50 yards before you can actually get the icon fully off a mapped road (if you're moving). Once stationary, it sometimes snaps back onto the road pointing in a direction of travel.

    See more here...

    https://www.tomtomforums.com/showthread.php?t=4925
     
    sparky672, Dec 7, 2007
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