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Skippy
Pocket GPS Verifier
Joined: 24/06/2003 00:22:12
Posts: 2946
Location: Escaped to the Antipodies! 36.83°S 174.75°E
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 Posted: Tue Mar 14, 2006 3:19 pm Post subject: |
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| noddy wrote: | | Whats baffling me is why the algorithym should want to take me so far out of my way on a route that is over 3 minutes longer and tell me it is the "fastest" but when I put in a different destination but an identical route (apart from the extra 2 miles) it then calculates it correctly. |
Only Garmin knows the answer to this question but quite a few suggestions have been put forward and I think they are a fair summary of what's going on when you get odd routes.
1. In an effort to strike a balance between a fast route calculation and a good route, the Gamin doesn't do an exhaustive search of every possible route to your destination. Depending on a number of factors, it may choose a route which is 10% longer than the actual fastest or shortest route. Some Garmin models acutally allow you to choose one of several options between Best Route and Quckest Calculation. The i3 seems to have a hard coded compromise which you can't change.
2. Some roads are not coded correctly by Navteq who supply the maps to Garmin. This causes the Garmin units to occasionally route down a single track country lane when a "B" road runs parallel to it.
If it really bugs you then try this experiment. Drive the route 10 times at different times of the day and use a stopwatch to time how long it takes. Now try driving the alternative route 10 times and see how long that takes.
Compare the times and the deviation from the mean time taken. I'm sure you will find that it can change by several minutes depending on a number of factors. If the time taken to drive the route varies by 5 minutes then the +/- 3 minute variation in the time that the Garmin gives as it's ESTIMATED time of arrival is neither here nor there.
If you are still not convinced, then switch the Garmin off and try driving to a destination you haven't been to before with your missus reading the map and see how long that takes. 
My Garmin works, it has it's quirks and it's routes are not perfect but it's 100 times easier to use than a paper map. And the wife loves it. That's good enough for me!
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Gone fishing! |
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Almahadeus
Frequent Visitor
Joined: Aug 06, 2005
Posts: 346
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| Posted: Tue Mar 14, 2006 3:25 pm Post subject: |
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| Skippy wrote: | | noddy wrote: | | Whats baffling me is why the algorithym should want to take me so far out of my way on a route that is over 3 minutes longer and tell me it is the "fastest" but when I put in a different destination but an identical route (apart from the extra 2 miles) it then calculates it correctly. |
If you are still not convinced, then switch the Garmin off and try driving to a destination you haven't been to before with your missus reading the map and see how long that takes. |
Well said Skippy. |
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ride4smilesjonny
Regular Visitor
Joined: Dec 29, 2005
Posts: 222
Location: teesside
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| Posted: Tue Mar 14, 2006 4:36 pm Post subject: |
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With you 100% skip!
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Hi ho - Hi ho its off to Arran i go,
with my i3 and a cup of tea hi ho, hi ho
hi ho hi ho.....
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www.ride4smiles.co.uk
£3500 raised in two weeks! :-) |
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TomDavison
Lifetime Member
Joined: Mar 02, 2006
Posts: 384
Location: Bedford, England
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| Posted: Wed Mar 15, 2006 1:55 pm Post subject: |
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Skippy wrote:
If you are still not convinced, then switch the Garmin off and try driving to a destination you haven't been to before with your missus reading the map and see how long that takes.
Don't forget to ask for the estimated time of arrival (to within a few seconds would probably be acceptable), and for regular updates on any variation to the previously calculated arrival time. And if you do ignore her instructions remind her that "turn around when possible" is much more acceptable than vitriol and a smack round the head with a road map. |
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slartibartfast
Occasional Visitor
Joined: Jan 19, 2006
Posts: 33
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| Posted: Thu Mar 16, 2006 11:19 am Post subject: |
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Just got my v8 maps back (nine days and I phoned Garmin on the eighth day) and I thought I would try a route which had produced unusual routes using v7. The result was that a route from Ware in Hertfordshire to Nottingham on both shortest and fastest was 130 miles (v7 and v8 ). The RAC
routeplanner finds a a shortest route of 106 miles. That's a difference of almost 20%. Has anybody elese found a discrepancy as large as this.
At least it's nice to have the new A120 and A10 bypass on the new maps so any routes to suffolk don't take you on 50 miles of back roads. |
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slartibartfast
Occasional Visitor
Joined: Jan 19, 2006
Posts: 33
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| Posted: Thu Mar 16, 2006 7:33 pm Post subject: |
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In my last post I stated that fastest and shortest routes were exactly the same from Ware to Nottingham. I have since tried a route from Ware station to Nottingham and the shortest route is 107 miles which agrees well with the RAC website. Ware station is only 50 yards from the location I tried the original route from and in fact the "longer" shortest route takes me past the station. The fastest route in both cases follows the A1 to the M25 and the M1 rather that take the M10. Adding a via at the M10 reduce the distance by 7 miles and the time by 9 minutes. I thought that maybe "faster" might mean higher average speed for the journey but in this case the average speed using the M10 was 59.04mph and the A1/M25/M1 averaged 58.65mph.
PS How do you produce those white quote boxes? |
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005clive
Regular Visitor
Joined: Mar 03, 2006
Posts: 65
Location: Penryn, Cornwall
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| Posted: Thu Mar 16, 2006 8:04 pm Post subject: |
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| slartibartfast wrote: |
PS How do you produce those white quote boxes? |
In the top right hand of a post you will see a quote box - click it will do the rest |
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slartibartfast
Occasional Visitor
Joined: Jan 19, 2006
Posts: 33
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| Posted: Thu Mar 16, 2006 8:12 pm Post subject: |
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005clive wrote
| Quote: | | In the top right hand of a post you will see a quote box - click it will do the rest |
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Thanks 005clive. Having javascript turned off in firefox didn't help either. Turned it on , now it works. |
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