The difference in mileage between GPS and Jeep
07-23-2009, 11:15 AM
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The difference in mileage between GPS and Jeep
I went on a road trip a couple weeks ago. I have a portable Magellan GPS. According to that, my trip was 1606 miles. According to Jeep's trip meter it was 1558 miles.
Any idea what could cause the difference? I am guessing the Jeep's mileage is correct. I hontestly don't really care, but I was just curious why it makes such a difference.
Any idea what could cause the difference? I am guessing the Jeep's mileage is correct. I hontestly don't really care, but I was just curious why it makes such a difference.
07-23-2009, 02:31 PM
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Went up to Missouri a couple of weeks ago and we have the one that attaches to the windshield. It tried to send us 12 miles down a 2 block dead end road. Other then that very helpful. I have the H20 hand held "water resistant" don't believe it. We use it for offshore fishing and it will point us in the right direction but show a different distance everytime. I would trust the Jeep instead unless you changed tire size.
07-23-2009, 03:23 PM
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The wonderful GPS vs. Odometer debate. Let me put it this way. Neither is really all that accurate. I read somewhere between 5 and 10% off on both of them. Lets look at both.
Odometer first. All that thing does is count rotations, depending where it is hooked up, wheel rotations, gear rotations, etc. Unless it is broken, it will accurately count the rotations it is supposed to count and then translate them into miles driven. However, there are lots of factors that can make them inaccurate. Tire inflation, tire size, tire wear, gear changes, etc. all play into accuracy. For that matter, even road irregularities play into the inaccuracy - your tire is not traveling in a straight line on a rough road, it is also traveling up and down road imperfections and bouncing or slipping a bit, and, while it may seem minor, combined with the other factors, leads to inaccuracy.
Now for the almighty GPS. Only with a GPS can you get really lost. These things have inaccuracy built right in, and show you how inaccurate they are. Play around with it and it will show you that it says something like "accurate to 10m." That means it thinks you are somewhere within a circle with a 20m diameter (10m radius). So, if it 10m off from the start point, and you walk 10m, and then it is again 10m off, but not in the same direction that it was on the start point, it could very well say you just walked 30m. Then factor drift into the formula. The GPS recalculates your position in reference to the satellites so many times every second, and combined with that aforementioned accuracy issue, it may think you are moving while standing still. Have you ever noticed that it sometimes thinks you are moving while you are sitting at a light? And then there are blind spots, when you lose signal because of a tunnel or something. When it gets a signal again, all it can do is calculate straight line distance from where you were to where you are, even though you just had lots of s curves. Yes, the GPS devices use really fancy algorithms to try and compensate and minimize drift and plot you along a map, etc., but there is still error.
So, yes, expect a difference between odometer and GPS. Which one is right? Which one is more accurate? In all reality, they both have similar tolerances for error. On a road trip, I would be more inclined to lean towards the odometer. On an off road trip, I would rely more on the GPS. If you really want, pull out a map and measure the distance and compare, or plug it into one of the online driving directions and see what it gives for mileage.
Odometer first. All that thing does is count rotations, depending where it is hooked up, wheel rotations, gear rotations, etc. Unless it is broken, it will accurately count the rotations it is supposed to count and then translate them into miles driven. However, there are lots of factors that can make them inaccurate. Tire inflation, tire size, tire wear, gear changes, etc. all play into accuracy. For that matter, even road irregularities play into the inaccuracy - your tire is not traveling in a straight line on a rough road, it is also traveling up and down road imperfections and bouncing or slipping a bit, and, while it may seem minor, combined with the other factors, leads to inaccuracy.
Now for the almighty GPS. Only with a GPS can you get really lost. These things have inaccuracy built right in, and show you how inaccurate they are. Play around with it and it will show you that it says something like "accurate to 10m." That means it thinks you are somewhere within a circle with a 20m diameter (10m radius). So, if it 10m off from the start point, and you walk 10m, and then it is again 10m off, but not in the same direction that it was on the start point, it could very well say you just walked 30m. Then factor drift into the formula. The GPS recalculates your position in reference to the satellites so many times every second, and combined with that aforementioned accuracy issue, it may think you are moving while standing still. Have you ever noticed that it sometimes thinks you are moving while you are sitting at a light? And then there are blind spots, when you lose signal because of a tunnel or something. When it gets a signal again, all it can do is calculate straight line distance from where you were to where you are, even though you just had lots of s curves. Yes, the GPS devices use really fancy algorithms to try and compensate and minimize drift and plot you along a map, etc., but there is still error.
So, yes, expect a difference between odometer and GPS. Which one is right? Which one is more accurate? In all reality, they both have similar tolerances for error. On a road trip, I would be more inclined to lean towards the odometer. On an off road trip, I would rely more on the GPS. If you really want, pull out a map and measure the distance and compare, or plug it into one of the online driving directions and see what it gives for mileage.
07-23-2009, 10:29 PM
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Thanks
Thank you guys for your replys.
Red, your explanation was very detailed and it made sense for the most of part. How do you know all things about GPS? These things are still amazing even with those flaws. It made my road trip 1000x easier than without it.
Red, your explanation was very detailed and it made sense for the most of part. How do you know all things about GPS? These things are still amazing even with those flaws. It made my road trip 1000x easier than without it.
07-23-2009, 10:33 PM
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did the test one's here in belgium , went to italy with 5 gps with the same destination, not one of the 5 gps systems gave the same speed or altitude , only two of them took the same route .
1 fixed blaupunkt dvd navi , 2 x portable blauwpunkt , 1 x garmin 278 and 1 garmin zumo
1 fixed blaupunkt dvd navi , 2 x portable blauwpunkt , 1 x garmin 278 and 1 garmin zumo
08-11-2009, 04:58 AM
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I use these things extensively in Africa for mapping among other things. Yes, they are amazing, but when you are trying to find the same point for the second time in the Sahara, you just want to throw them out of the window and smash them into a million pieces. Even the best of them can't seem to find the same point twice.
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08-11-2009, 07:05 PM
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The wonderful GPS vs. Odometer debate. Let me put it this way. Neither is really all that accurate. I read somewhere between 5 and 10% off on both of them. Lets look at both.
Odometer first. All that thing does is count rotations, depending where it is hooked up, wheel rotations, gear rotations, etc. Unless it is broken, it will accurately count the rotations it is supposed to count and then translate them into miles driven. However, there are lots of factors that can make them inaccurate. Tire inflation, tire size, tire wear, gear changes, etc. all play into accuracy. For that matter, even road irregularities play into the inaccuracy - your tire is not traveling in a straight line on a rough road, it is also traveling up and down road imperfections and bouncing or slipping a bit, and, while it may seem minor, combined with the other factors, leads to inaccuracy.
Now for the almighty GPS. Only with a GPS can you get really lost. These things have inaccuracy built right in, and show you how inaccurate they are. Play around with it and it will show you that it says something like "accurate to 10m." That means it thinks you are somewhere within a circle with a 20m diameter (10m radius). So, if it 10m off from the start point, and you walk 10m, and then it is again 10m off, but not in the same direction that it was on the start point, it could very well say you just walked 30m. Then factor drift into the formula. The GPS recalculates your position in reference to the satellites so many times every second, and combined with that aforementioned accuracy issue, it may think you are moving while standing still. Have you ever noticed that it sometimes thinks you are moving while you are sitting at a light? And then there are blind spots, when you lose signal because of a tunnel or something. When it gets a signal again, all it can do is calculate straight line distance from where you were to where you are, even though you just had lots of s curves. Yes, the GPS devices use really fancy algorithms to try and compensate and minimize drift and plot you along a map, etc., but there is still error.
So, yes, expect a difference between odometer and GPS. Which one is right? Which one is more accurate? In all reality, they both have similar tolerances for error. On a road trip, I would be more inclined to lean towards the odometer. On an off road trip, I would rely more on the GPS. If you really want, pull out a map and measure the distance and compare, or plug it into one of the online driving directions and see what it gives for mileage.
Odometer first. All that thing does is count rotations, depending where it is hooked up, wheel rotations, gear rotations, etc. Unless it is broken, it will accurately count the rotations it is supposed to count and then translate them into miles driven. However, there are lots of factors that can make them inaccurate. Tire inflation, tire size, tire wear, gear changes, etc. all play into accuracy. For that matter, even road irregularities play into the inaccuracy - your tire is not traveling in a straight line on a rough road, it is also traveling up and down road imperfections and bouncing or slipping a bit, and, while it may seem minor, combined with the other factors, leads to inaccuracy.
Now for the almighty GPS. Only with a GPS can you get really lost. These things have inaccuracy built right in, and show you how inaccurate they are. Play around with it and it will show you that it says something like "accurate to 10m." That means it thinks you are somewhere within a circle with a 20m diameter (10m radius). So, if it 10m off from the start point, and you walk 10m, and then it is again 10m off, but not in the same direction that it was on the start point, it could very well say you just walked 30m. Then factor drift into the formula. The GPS recalculates your position in reference to the satellites so many times every second, and combined with that aforementioned accuracy issue, it may think you are moving while standing still. Have you ever noticed that it sometimes thinks you are moving while you are sitting at a light? And then there are blind spots, when you lose signal because of a tunnel or something. When it gets a signal again, all it can do is calculate straight line distance from where you were to where you are, even though you just had lots of s curves. Yes, the GPS devices use really fancy algorithms to try and compensate and minimize drift and plot you along a map, etc., but there is still error.
So, yes, expect a difference between odometer and GPS. Which one is right? Which one is more accurate? In all reality, they both have similar tolerances for error. On a road trip, I would be more inclined to lean towards the odometer. On an off road trip, I would rely more on the GPS. If you really want, pull out a map and measure the distance and compare, or plug it into one of the online driving directions and see what it gives for mileage.
08-12-2009, 02:00 PM
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You can select either "shortest" or "fastest" route on most GPS systems....fastest is usually the default. For a trip of that length, the fastest route may have been sufficiently different than the route you actually took to make up the difference.