Resolution to one mile per hour, compares well with my new cars.
GPS gets around errors related to tire diameter variation due to, inflation, wear, loading, and speed. Also, there is tire slip when wet or rough terrain.
Surely a GPS speedo just measures localized ds/dt? As long as the difference between x1, y1 and x2, y2 used to determine ds are not a huge distance apart then any error in their true location is immaterial isn't it? The distance measurement itself should be fairly accurate shouldn't it?
Surely a GPS speedo just measures localized ds/dt?
Conceptually, Yes.
In practice, probably not.
Although the GPS uses trilateralization to determine location, at low speeds and therefore short distances traveled between successive measurements, the error of the delta distance, and therefore heading and velocity become significant.
Many GPS units, I think, actually use the Doppler shift in the received signal to measure velocity.
There are GPS speedometers on the market. Custom vehicles like street rods use them for ease of installation, and lack of calibration requirements when changing gear ratios, tire diameters.
Y'all know this is a 10 year old resurrected don't you?
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TopYes - see #44 ...
EDIT
Perhaps all the banter from #36 on should be split to "Off-topic" ...
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TopResolution to one mile per hour, compares well with my new cars.
GPS gets around errors related to tire diameter variation due to, inflation, wear, loading, and speed. Also, there is tire slip when wet or rough terrain.
It all starts with a mental vision.
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TopResolution != Accuracy
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TopSurely a GPS speedo just measures localized ds/dt? As long as the difference between x1, y1 and x2, y2 used to determine ds are not a huge distance apart then any error in their true location is immaterial isn't it? The distance measurement itself should be fairly accurate shouldn't it?
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TopSo long as the position error is consistent...
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TopConceptually, Yes.
In practice, probably not.
Although the GPS uses trilateralization to determine location, at low speeds and therefore short distances traveled between successive measurements, the error of the delta distance, and therefore heading and velocity become significant.
Many GPS units, I think, actually use the Doppler shift in the received signal to measure velocity.
JC
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TopThere are GPS speedometers on the market. Custom vehicles like street rods use them for ease of installation, and lack of calibration requirements when changing gear ratios, tire diameters.
http://www.speedhut.com/gauges/Speedometers/GPS-Speedometers/?catid=f8|f37
It all starts with a mental vision.
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TopThe GPS speed on my phone matches quite will with the speedo on my car, and with the cycle computer on my wife's bike. Within 1 km/h.
"Experience is what enables you to recognise a mistake the second time you make it."
"Good judgement comes from experience. Experience comes from bad judgement."
"Wisdom is always wont to arrive late, and to be a little approximate on first possession."
"When you hear hoofbeats, think horses, not unicorns."
"Fast. Cheap. Good. Pick two."
"Read a lot. Write a lot."
"We see a lot of arses on handlebars around here." - [J Ekdahl]
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Top"Many GPS units, I think, actually use the Doppler shift in the received signal to measure velocity."
I did not know that. Thanks.
Quebracho seems to be the hardest wood.
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TopSome interesting reading:
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html
https://en.wikipedia.org/wiki/Differential_GPS
https://en.wikipedia.org/wiki/Real_Time_Kinematic
https://www.google.ca/search?q=how+does+gps+calculate+speed
https://www.quora.com/How-does-GPS-calculate-our-exact-speed-while-moving
https://www.telogis.com/blog/gps-tracking-report-speeding
http://gpsinformation.net/main/gpsspeed.htm
https://www.e-education.psu.edu/geog862/node/1786
http://gpsworld.com/rtk-on-your-smartphone-or-tablet/
Don't believe everything you read on the Internet ;-)
"Experience is what enables you to recognise a mistake the second time you make it."
"Good judgement comes from experience. Experience comes from bad judgement."
"Wisdom is always wont to arrive late, and to be a little approximate on first possession."
"When you hear hoofbeats, think horses, not unicorns."
"Fast. Cheap. Good. Pick two."
"Read a lot. Write a lot."
"We see a lot of arses on handlebars around here." - [J Ekdahl]
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