Synchronize GPS and cyclocomputer
10-22-19, 06:53 PM
#26
Senior Member
Distance traveled is an ever elusive, and, perhaps illusive, quantity.
Ride through a puddle in a dry parking lot and make a few turns. You will notice that the rear wheel track cuts inside the front wheel, so it travelled a shorter distance. Which one was the true distance?
As yo travel down the road, the front wheel makes constant, small excursions left and right, thus it travels farther than the rear wheel.
If you calibrate your 'puter to agree with your GPS it will be measuring a shorter distance than it actually rolls.
If you are following a RWGPS route you, or someone planned out, the straight lines between points may underestimate the distance rolled by the bike.
Now, for a little icing on this cupcake, let your tires' radii change subtly with temperature, inflation, and load.
Have fun
Ride through a puddle in a dry parking lot and make a few turns. You will notice that the rear wheel track cuts inside the front wheel, so it travelled a shorter distance. Which one was the true distance?
As yo travel down the road, the front wheel makes constant, small excursions left and right, thus it travels farther than the rear wheel.
If you calibrate your 'puter to agree with your GPS it will be measuring a shorter distance than it actually rolls.
If you are following a RWGPS route you, or someone planned out, the straight lines between points may underestimate the distance rolled by the bike.
Now, for a little icing on this cupcake, let your tires' radii change subtly with temperature, inflation, and load.
Have fun
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10-22-19, 07:24 PM
#27
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Distance traveled is an ever elusive, and, perhaps illusive, quantity.
Ride through a puddle in a dry parking lot and make a few turns. You will notice that the rear wheel track cuts inside the front wheel, so it travelled a shorter distance. Which one was the true distance?
As yo travel down the road, the front wheel makes constant, small excursions left and right, thus it travels farther than the rear wheel.
If you calibrate your 'puter to agree with your GPS it will be measuring a shorter distance than it actually rolls.
If you are following a RWGPS route you, or someone planned out, the straight lines between points may underestimate the distance rolled by the bike.
Now, for a little icing on this cupcake, let your tires' radii change subtly with temperature, inflation, and load.
Have fun
Ride through a puddle in a dry parking lot and make a few turns. You will notice that the rear wheel track cuts inside the front wheel, so it travelled a shorter distance. Which one was the true distance?
As yo travel down the road, the front wheel makes constant, small excursions left and right, thus it travels farther than the rear wheel.
If you calibrate your 'puter to agree with your GPS it will be measuring a shorter distance than it actually rolls.
If you are following a RWGPS route you, or someone planned out, the straight lines between points may underestimate the distance rolled by the bike.
Now, for a little icing on this cupcake, let your tires' radii change subtly with temperature, inflation, and load.
Have fun
10-22-19, 08:28 PM
#29
Full Member
10-22-19, 08:33 PM
#30
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That's like saying that I hit the bulls-eye every time I throw a dart (to the best of my ability), even when it hits the floor. Clue: there's nothing exact about distance calculated from GPS PVT data.
10-23-19, 12:18 PM
#31
Full Member
My point is very simple: the a GPS device uses satellite signal to calculate a 3D position fix. And this 3D position fix is exactly what the device is using to determine speed and distance traveled. Contrary to the claims made by some previous posters, the GPS device do not make any attempts to project that 3D position onto some model of the Earth's surface.
Absolutely wrong. Unless a GPS device is deliberately sabotaged, it obeys the typical statistical laws of normal distribution. Simply speaking averaging the results of N measurements increases the precision sqrt(N) times. A position fix can be made arbitrarily precise by averaging a sufficient number of discrete position polls. Measurements that inherently involve a large number of position polls, like distance or speed, are very precise out of the box for that very reason.
10-23-19, 02:04 PM
#32
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It is like saying that there can't be anything exact in this world at all.
My point is very simple: the a GPS device uses satellite signal to calculate a 3D position fix. And this 3D position fix is exactly what the device is using to determine speed and distance traveled. Contrary to the claims made by some previous posters, the GPS device do not make any attempts to project that 3D position onto some model of the Earth's surface.
Absolutely wrong. Unless a GPS device is deliberately sabotaged, it obeys the typical statistical laws of normal distribution. Simply speaking averaging the results of N measurements increases the precision sqrt(N) times. A position fix can be made arbitrarily precise by averaging a sufficient number of discrete position polls. Measurements that inherently involve a large number of position polls, like distance or speed, are very precise out of the box for that very reason.
My point is very simple: the a GPS device uses satellite signal to calculate a 3D position fix. And this 3D position fix is exactly what the device is using to determine speed and distance traveled. Contrary to the claims made by some previous posters, the GPS device do not make any attempts to project that 3D position onto some model of the Earth's surface.
Absolutely wrong. Unless a GPS device is deliberately sabotaged, it obeys the typical statistical laws of normal distribution. Simply speaking averaging the results of N measurements increases the precision sqrt(N) times. A position fix can be made arbitrarily precise by averaging a sufficient number of discrete position polls. Measurements that inherently involve a large number of position polls, like distance or speed, are very precise out of the box for that very reason.
