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(07-25-2014, 01:47 PM)pekingduck_imp Wrote: Can we assume GPS to be 100% accurate? If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Here are a couple questions I'd have that may account for some inaccuracies why GPS might record lower mileage. Sorry in advance for the rambling.
GPS devices rely on transmitted signals that can be interupted by trees, clouds, tunnels etc.
You're in tight twisties with tree cover, GPS loses signal for a couple secs, recovers and jumped across the ravine while you ran a hundred feet farther and back. It also does not track elevation well.
You go over a slight rise, down a little drop, and the difference is that you went a little farther than the crow flies.
Rear tire slippage. It occurs all the time, even though we don't feel it. It's the main (only?) reason tires wear.
One last point, a small one, maybe crazy. GPS is mounted at a fixed point, lets say along the centerline of the bike. As you lean, the GPS is moved a foot or two to the inside of the turn, and thus is going around a smaller radius, meaning a little less distance traveled.
Your mileage WILL vary.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
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My speedometer reads 70 mph and gps reads 69 mph. My suzuki dr 650 speedo reads 70 mph but gps reads 65 mph, so cb speedo is pretty much right on target.
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(07-28-2014, 08:44 AM)AzBob_imp Wrote: (07-25-2014, 01:47 PM)pekingduck_imp Wrote: Can we assume GPS to be 100% accurate? If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Here are a couple questions I'd have that may account for some inaccuracies why GPS might record lower mileage. Sorry in advance for the rambling.
GPS devices rely on transmitted signals that can be interupted by trees, clouds, tunnels etc.
You're in tight twisties with tree cover, GPS loses signal for a couple secs, recovers and jumped across the ravine while you ran a hundred feet farther and back. It also does not track elevation well.
You go over a slight rise, down a little drop, and the difference is that you went a little farther than the crow flies.
Rear tire slippage. It occurs all the time, even though we don't feel it. It's the main (only?) reason tires wear.
One last point, a small one, maybe crazy. GPS is mounted at a fixed point, lets say along the centerline of the bike. As you lean, the GPS is moved a foot or two to the inside of the turn, and thus is going around a smaller radius, meaning a little less distance traveled.
Your mileage WILL vary.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
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Plus doesn't a gps unit connect to multiple satellites rendering the chance of losing a signal almost noon existent...
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(07-28-2014, 10:42 AM)The ferret_imp Wrote: (07-28-2014, 08:44 AM)AzBob_imp Wrote: (07-25-2014, 01:47 PM)pekingduck_imp Wrote: Can we assume GPS to be 100% accurate? If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Here are a couple questions I'd have that may account for some inaccuracies why GPS might record lower mileage. Sorry in advance for the rambling.
GPS devices rely on transmitted signals that can be interupted by trees, clouds, tunnels etc.
You're in tight twisties with tree cover, GPS loses signal for a couple secs, recovers and jumped across the ravine while you ran a hundred feet farther and back. It also does not track elevation well.
You go over a slight rise, down a little drop, and the difference is that you went a little farther than the crow flies.
Rear tire slippage. It occurs all the time, even though we don't feel it. It's the main (only?) reason tires wear.
One last point, a small one, maybe crazy. GPS is mounted at a fixed point, lets say along the centerline of the bike. As you lean, the GPS is moved a foot or two to the inside of the turn, and thus is going around a smaller radius, meaning a little less distance traveled.
Your mileage WILL vary.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
Both, I think.
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(07-28-2014, 08:26 PM)Cormanus_imp Wrote: (07-28-2014, 10:42 AM)The ferret_imp Wrote: (07-28-2014, 08:44 AM)AzBob_imp Wrote: (07-25-2014, 01:47 PM)pekingduck_imp Wrote: Can we assume GPS to be 100% accurate? If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Here are a couple questions I'd have that may account for some inaccuracies why GPS might record lower mileage. Sorry in advance for the rambling.
GPS devices rely on transmitted signals that can be interupted by trees, clouds, tunnels etc.
You're in tight twisties with tree cover, GPS loses signal for a couple secs, recovers and jumped across the ravine while you ran a hundred feet farther and back. It also does not track elevation well.
You go over a slight rise, down a little drop, and the difference is that you went a little farther than the crow flies.
Rear tire slippage. It occurs all the time, even though we don't feel it. It's the main (only?) reason tires wear.
One last point, a small one, maybe crazy. GPS is mounted at a fixed point, lets say along the centerline of the bike. As you lean, the GPS is moved a foot or two to the inside of the turn, and thus is going around a smaller radius, meaning a little less distance traveled.
Your mileage WILL vary.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
Both, I think.
Yes.
Quote:If there were 5 different GPS devices in the same car, would they all read the same after 100 miles?
Read the same what? The GPS speed indicator is a "moment in time" calculation. It doesn't store your starting position and calculate the distance from it, that wouldn't work at all. In any given moment, it is calculating the distance from the last time it did it (tenths of a second), and telling you your speed. You can't change your altitude fast enough, lean enough, or whatever in that tiny timeslice to matter.
I believe he is talking distance traveled, not speed.
Both, I think.
No, just distance. I am not sure why it is assumed that GPS is 100% accurate. Is the cheapest GPS as accurate as an expensive one? Can it not be improved upon? Is an iphone as accurate? Atmospheric conditions, reflections off mountains or buildings, even trees affect or block the signal.
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