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aterlecki Occasional Visitor
Joined: Nov 25, 2004 Posts: 1
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Posted: Fri Nov 26, 2004 1:05 am Post subject: Swivelling map when coming to a halt |
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I'm wondering if my Go has a fault because many times, as I am coming to a halt, the map which is usually oriented correctly and showing my direction of travel suddenly starts to swivel around. I can actually have it so when stopped the map is pointing at 90 degrees from where I am going and it only corrects itself once I start driving off again. This can be very confusing at certain junctions when suddenly I can get a bit disoriented.
I know when the Go is first turned on it might be pointing in the wrong direction (although why they couldn't fit a small compass to the unit to overcome this I don't know) but it seems strange that it swivels after I've been moving and just come to a halt, say at a traffic light or junction.
Is this map swivel characteristic a "feature" of the Go unit or is my unit faulty? What does yours do? |
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manicguitarist Occasional Visitor
Joined: Oct 29, 2004 Posts: 15
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Posted: Fri Nov 26, 2004 9:40 am Post subject: |
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I have seen this happen when GPS reception is poor and the unit tries to guess which way you are facing. |
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nej Frequent Visitor
Joined: Jun 16, 2004 Posts: 454 Location: London, Ingerlund
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Posted: Fri Nov 26, 2004 9:43 am Post subject: Re: Swivelling map when coming to a halt |
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aterlecki wrote: | I'm wondering if my Go has a fault because many times, as I am coming to a halt, the map which is usually oriented correctly and showing my direction of travel suddenly starts to swivel around. I can actually have it so when stopped the map is pointing at 90 degrees from where I am going and it only corrects itself once I start driving off again. This can be very confusing at certain junctions when suddenly I can get a bit disoriented.
I know when the Go is first turned on it might be pointing in the wrong direction (although why they couldn't fit a small compass to the unit to overcome this I don't know) but it seems strange that it swivels after I've been moving and just come to a halt, say at a traffic light or junction.
Is this map swivel characteristic a "feature" of the Go unit or is my unit faulty? What does yours do? |
Maybe you shouldn't use the handbrake so much in your parking! :D |
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Sniff Regular Visitor
Joined: Nov 02, 2004 Posts: 123 Location: Munich, Germany
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Posted: Fri Nov 26, 2004 10:55 am Post subject: |
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I can't say that I've ever noticed that problem myself.
How would a small compass help though? |
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BanziBarn Regular Visitor
Joined: Jun 24, 2004 Posts: 82
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Posted: Fri Nov 26, 2004 2:22 pm Post subject: |
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Mine does that too. I'd put it down to poor reception. |
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carl_w Lifetime Member
Joined: Mar 13, 2004 Posts: 242
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Posted: Fri Nov 26, 2004 3:15 pm Post subject: |
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Every position fix that comes out of the GPS is a little bit out. If you plot a distribution of these you'll get a kind of 3D normal distribution, with the actual position at the "peak".
So if on one poll you get a position that's say 3 ft East of your actual position, and on the next poll you get a position that's 3 ft West of your actual position, Tomtom will think you're travelling East to West and rotate the map accordingly. Obviously the less precision (i.e. less satellites) you have, the greater this effect is likely to be., |
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Juey Occasional Visitor
Joined: Sep 09, 2004 Posts: 46
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Posted: Fri Nov 26, 2004 4:11 pm Post subject: |
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I'm with aterlecki on this one
Once I've stopped the arrow points 90 degrees right.
It's as if the receiver points east- west in the unit rather than north- south (when screen facing you and pointing ahead is north) It's only when it's moving that it recognises you're pinting the other way.
It always does it, even when 5 bars are lit for reception.
Maybe it's the camber on the road, my driveway also cambers heavily to the left (unit down on left hand side)
Not a problem I'm worried about though |
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DavidW Pocket GPS Moderator
Joined: 17/05/2003 02:26:21 Posts: 3747 Location: Bedfordshire, UK
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Posted: Fri Nov 26, 2004 7:48 pm Post subject: |
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The precision is dependent not only on the number of satellites in the fix, but on the geometry of the satellites - as well as various other factors, such as ionospheric disturbances.
David |
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Dave Frequent Visitor
Joined: Sep 10, 2003 Posts: 6460 Location: UK
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Posted: Fri Nov 26, 2004 8:09 pm Post subject: |
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Personally I would disable ASN |
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Frazzle Regular Visitor
Joined: Nov 05, 2004 Posts: 66
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Posted: Fri Nov 26, 2004 10:36 pm Post subject: How a GPS works ! |
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Hi folks,
Just a quick comment on this one ...
GPS systems plot positions
Changes in the plotted position provide velocity and beearing data that the TTG uses to show your direction of TRAVEL
If the TTG is stationary there is theoretically no change of position so the direction of travel is not known. TTG will then randomly hunt until you begin moving agian.
Be aware ... the GPS antenna in the TTG is a Ceramic patch with a hemispherical reception plot. IT IS NOT DIRECTIONAL. The GPS does not use it's patch antenna as a "radio direction finder".
Hope this helps.
Oh and the "loss of signal velocity and direction prediction " system, if it works, should not effect direction plotting as the GPS signal is present and you are NOT moving. It uses hardware acceleromters to detect changes in velocity. No movement = no change. |
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wildcard Occasional Visitor
Joined: Nov 13, 2004 Posts: 44
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Posted: Mon Nov 29, 2004 11:58 pm Post subject: |
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As others have said GPS systems plot position - it calculates direction (and speed ) by comparing positions at very short time intervals . Also commercial GPS has a margin of error of say 3 meters radius or so . You can imagine at low speed the fuzziness ( circle of error ) of one position overlaps the fuzziness of the next giving the unit an number of different possibilities within split seconds , hence it swivels around . At higher speeds the margins of error cease to overlap and the readout would become more accurate - particularly if the software applied some weighting or smoothing to the results . For example if within 5 seconds , it calculated 5 results , 4 approximately the same , the 5th markedly different , it could discard it and combine the remaining 4 to make a running weighted average.
Do we know for sure a Go contains accelerometers ? - I would be seriously impressed if it did - at a guess I would have thought the ASN solution is purely a software based predictive tool based on what was happening moments before the signal was lost and as such would be fooled by sharp changes of direction - an underground junction would be the ideal test .
Geoff |
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