[CriticalThinker]

Can you link us to the full article? The last time we had a GPS accuracy article we saw that the authors tested a variety of different GPS devices which all showed different speed results, with an error range of over 20%, and then picked out the result closest to the result they wanted and declared that GPS was incredibly accurate, only differing from the real speed by 2%.

Irrelevant.

GPS speed accuracy on a single human over extremely short distance while making pinpoint turns does not apply to vehicular motion.  Unless you're claiming that a Boeing 747 is capable of making a 90 degree turn under 3 feet in radius.  The 20% you are hanging your hat on was instantaneous very rapid acceleration after making a turn as they state in the article.  Those physics simply can't apply to commercial airlines.

The ball is in your court again Tom.

Thank you,

CriticalThinker

The thing about GPS is that it provides a POSITION - accurate to around 10 feet (although dual antenna units get you down to 2 feet).  It's possible to "lose the signal" and wind up with insufficient satellites to get a good signal and stuff like that.

GPS doesn't give you speed (well, not directly at least).  The phone or handheld GPS receiver calculates speed by calculating distance between two Lat/Long position and dividing that distance by the time between the past readings.

Clearly for athletic events over "human" distances - this is a disaster.   If someone runs 100 feet in 10 seconds - and the GPS is "off" by 10 feet then the reading could say anything from 8 feet per second up to 12 feet per second...which is a horrific error.

However, if an airplane flies 2000 miles (10 million feet) and the GPS is off by 10 feet - then the error is at worst only 2 parts per million...utterly negligible.

So using data about the problems of measuring athletic event performance with GPS is laughably inapplicable to discussions about thousand mile journeys.

As usual, Mr Bishop is clutching at straws and hoping we're too stupid to notice!  SORRY TOM...WE'RE NOT STUPID.

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Unless someone wants to deny the existence of electromagnetic wave structure, then both GPS and Radar measure the same physics phenomenon and are both tested using metered tracks and stopwatches.

Triangulation, if memory serves me correctly was on the approved list of physically determining a relative point in space on a planar surface.

Thank You,

CriticalThinker

[Rounder]

Ok. I have been looking around and getting ready to start the Flight Time Map project, but have run into a bump.

I was wanting to use https://openflights.org to get flight time data, but I discovered that they just calculate the times based on distance.
In real-life this works perfectly, but I know that it will completely ruin the validity of my model in this forum.

I need times based on departures and arrivals of real passenger jets.  Please point me in the right direction to be able to find acceptable data.
Many thanks.

https://flightaware.com/

[3DGeek]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Are you sure that cellphones and hand-held GPS's do that?  I thought they just used position versus time.

I think I may know someone who can answer this comprehensively...I'll try to get the actual facts.

But it really doesn't matter.  The end result is the same.

[CriticalThinker]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Are you sure that cellphones and hand-held GPS's do that?  I thought they just used position versus time.

I think I may know someone who can answer this comprehensively...I'll try to get the actual facts.

But it really doesn't matter.  The end result is the same.

Radar analyzes a Doppler shift from a single point source.  GPS analyzes Doppler shift from 3 different point sources. Radar is more minutely accurate on short distance changes in acceleration because the waveform is a much higher frequency.

The frequency variations don't matter with straight lines or wide turn radii. That's why I made the statement about a 747 turning in the same kind of radius as a human.

Thank you,

CriticalThinker

[inquisitive]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Are you sure that cellphones and hand-held GPS's do that?  I thought they just used position versus time.

I think I may know someone who can answer this comprehensively...I'll try to get the actual facts.

But it really doesn't matter.  The end result is the same.

Radar analyzes a Doppler shift from a single point source.  GPS analyzes Doppler shift from 3 different point sources. Radar is more minutely accurate on short distance changes in acceleration because the waveform is a much higher frequency.

The frequency variations don't matter with straight lines or wide turn radii. That's why I made the statement about a 747 turning in the same kind of radius as a human.

Thank you,

CriticalThinker

Where in the NMEA output is speed?  What point sources?

[CriticalThinker]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Are you sure that cellphones and hand-held GPS's do that?  I thought they just used position versus time.

I think I may know someone who can answer this comprehensively...I'll try to get the actual facts.

But it really doesn't matter.  The end result is the same.

Radar analyzes a Doppler shift from a single point source.  GPS analyzes Doppler shift from 3 different point sources. Radar is more minutely accurate on short distance changes in acceleration because the waveform is a much higher frequency.

The frequency variations don't matter with straight lines or wide turn radii. That's why I made the statement about a 747 turning in the same kind of radius as a human.

Thank you,

CriticalThinker

Where in the NMEA output is speed?  What point sources?

I should have been a tad more specific. At least 3 point sources.

Example NMEA data:

$GPGGA,181908.00,3404.7041778,N,07044.3966270,
W,4 13,1.00,495.144,M,29.200,M,0.10,0000*40

13 would be the number of point sources. And it would be the delta in the 3404.70417 & 07044.3966270 that produce a Doppler shift effect for speed output. While the values are expressed in the format of lat/long. They are attained by a minimum of 3 signals for triangulation.  As each point source sends and electromagnetic radio wave to the radio antenna of the unit for triangulation, the validity on a flat/round earth remains consistent.  The waves come downward at an angle to the antenna instead of at ground level but the physics is the exact same as radar.

Thank you,

CriticalThinker

[JHelzer]

I need times based on departures and arrivals of real passenger jets.  Please point me in the right direction to be able to find acceptable data.

https://flightaware.com/

That is perfect.  Thank you.

[zp0okii]

I guess Tom didn't know what to say

[3DGeek]

I guess Tom didn't know what to say

No - he's utterly boxed in on this one.

Since we can prove airliner flight speeds - then he's not got a leg to stand on anymore...and even if we can't prove that the speeds are correct - we only need to prove that any error is "systematic" (ie that it applies everywhere).

[Tom Bishop]

Can you link us to the full article? The last time we had a GPS accuracy article we saw that the authors tested a variety of different GPS devices which all showed different speed results, with an error range of over 20%, and then picked out the result closest to the result they wanted and declared that GPS was incredibly accurate, only differing from the real speed by 2%.

The article in question was looking at people on a bicycle going around a track.  That is not even close to the use of GPS in aviation, maritime and even cars.  Straight from the horse's mouth, GPS and WAAS "gives position accuracy of better than 3 m, 95 percent of the time".   

http://www8.garmin.com/aboutGPS/waas.html


Any discussion of GPS accuracy of 3 meters not being good enough is just lazy and ridiculous.   Why don't you just try and help settle this without your silly arguments?

This article "Accuracy of non-differential GPS for the determination of speed over ground" is also about people going around a track. Why should we not trust that one but trust this one?

Can you link us to the full article? The last time we had a GPS accuracy article we saw that the authors tested a variety of different GPS devices which all showed different speed results, with an error range of over 20%, and then picked out the result closest to the result they wanted and declared that GPS was incredibly accurate, only differing from the real speed by 2%.

Irrelevant.

GPS speed accuracy on a single human over extremely short distance while making pinpoint turns does not apply to vehicular motion.  Unless you're claiming that a Boeing 747 is capable of making a 90 degree turn under 3 feet in radius.  The 20% you are hanging your hat on was instantaneous very rapid acceleration after making a turn as they state in the article.  Those physics simply can't apply to commercial airlines.

The ball is in your court again Tom.

Thank you,

CriticalThinker

This study we are talking about in this thread is about people on a track, with humans playing sports, like the other one was. Here is the link again of the one mentioned on the previous page. What are you talking about.   

[Tom Bishop]

The thing about GPS is that it provides a POSITION - accurate to around 10 feet (although dual antenna units get you down to 2 feet).  It's possible to "lose the signal" and wind up with insufficient satellites to get a good signal and stuff like that.

GPS doesn't give you speed (well, not directly at least).  The phone or handheld GPS receiver calculates speed by calculating distance between two Lat/Long position and dividing that distance by the time between the past readings.

Clearly for athletic events over "human" distances - this is a disaster.   If someone runs 100 feet in 10 seconds - and the GPS is "off" by 10 feet then the reading could say anything from 8 feet per second up to 12 feet per second...which is a horrific error.

However, if an airplane flies 2000 miles (10 million feet) and the GPS is off by 10 feet - then the error is at worst only 2 parts per million...utterly negligible.

So using data about the problems of measuring athletic event performance with GPS is laughably inapplicable to discussions about thousand mile journeys.

As usual, Mr Bishop is clutching at straws and hoping we're too stupid to notice!  SORRY TOM...WE'RE NOT STUPID.

Both studies are about people going around tracks. What are you talking about?

[Tom Bishop]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Unless someone wants to deny the existence of electromagnetic wave structure, then both GPS and Radar measure the same physics phenomenon and are both tested using metered tracks and stopwatches.

If that is how speeds are calculated, then that means that the GPS speed test is invalid in regards to this discussion about the shape of the earth since there is no Round Earth lat/lon speed test to compare it to in order to determine whether the Round Earth lat/lon coordinate system is correct.

[CriticalThinker]

Can you link us to the full article? The last time we had a GPS accuracy article we saw that the authors tested a variety of different GPS devices which all showed different speed results, with an error range of over 20%, and then picked out the result closest to the result they wanted and declared that GPS was incredibly accurate, only differing from the real speed by 2%.

The article in question was looking at people on a bicycle going around a track.  That is not even close to the use of GPS in aviation, maritime and even cars.  Straight from the horse's mouth, GPS and WAAS "gives position accuracy of better than 3 m, 95 percent of the time".   

http://www8.garmin.com/aboutGPS/waas.html


Any discussion of GPS accuracy of 3 meters not being good enough is just lazy and ridiculous.   Why don't you just try and help settle this without your silly arguments?

This article "Accuracy of non-differential GPS for the determination of speed over ground" is also about people going around a track. Why should we not trust that one but trust this one?

Can you link us to the full article? The last time we had a GPS accuracy article we saw that the authors tested a variety of different GPS devices which all showed different speed results, with an error range of over 20%, and then picked out the result closest to the result they wanted and declared that GPS was incredibly accurate, only differing from the real speed by 2%.

Irrelevant.

GPS speed accuracy on a single human over extremely short distance while making pinpoint turns does not apply to vehicular motion.  Unless you're claiming that a Boeing 747 is capable of making a 90 degree turn under 3 feet in radius.  The 20% you are hanging your hat on was instantaneous very rapid acceleration after making a turn as they state in the article.  Those physics simply can't apply to commercial airlines.

The ball is in your court again Tom.

Thank you,

CriticalThinker

This study we are talking about is about people on a track, with humans playing sports, like the other one was. Here is the link again of the one mentioned on the previous page. What are you talking about.   

You said a 20% error.  Here is the exact wording of the article.

The speed determined by the GPS receiver was within 0.2 ms−1 of the true speed measured for 45% of the values with a further 19% lying within 0.4 ms−1 (n=5060)

Do you know what an Analysis Of Variance (ANOVA) experiment is?  They take two groups and assess the differences between both groups to see if there is a statistical difference of the mean values for both groups.  Group A is measured with GPS.  Group B is measured with a mechanical measurement.  All 5060 samples are separated by group and the 2 bell curves are compared.  If 2 standard deviations from the mean fall under both overlapping bell curves, then there is not statistical difference in the two groups.  This is higher level statistical analysis that most undergraduates wouldn't see so it's ok if you're not familiar with this methodology.

Please point out the 20% margin of error that you were speaking about in this experiment.

Thank you,

CriticalThinker

[CriticalThinker]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Unless someone wants to deny the existence of electromagnetic wave structure, then both GPS and Radar measure the same physics phenomenon and are both tested using metered tracks and stopwatches.

If that is how speeds are calculated, then that means that the GPS speed test is invalid in regards to this discussion about the shape of the earth since there is no Round Earth lat/lon speed test to compare it to in order to determine whether the Round Earth lat/lon coordinate system is correct.

Expressed and calculated are two very different words Tom.  Relative position from triangulation via doppler effect is a valid method on a flat plane.  3 radar guns pointed at an object from 3 different angles will accomplish the same thing.  Absolute position doesn't matter.  Change in relative position between 2 metered times as triangulated using the bounce back of waved electromagnetic signals is consistent with the FE constraints.

And let's not forget it is calibration tested against a flat metered track and mechanical time piece.

I'm not letting you off that easy Tom.  Play with the words all you like but the doppler shift can't be explained away.

Thank you,

CriticalThinker

[Curious Squirrel]

This is a huge sticking point in every single one of your arguments, but you never answer the simple question. What exactly is the difference in length between a flat Earth mile, and a round Earth mile? If the difference is less than 5% (considering in one mile there is a drop of less than an inch I would suspect so) then this entire issue is without ground to stand on. A 5% difference would result in a difference of only 100 miles over a 2,000 mile flight. That's not enough to help solve the quadrilateral problem, unless I'm sorely mistaken.

So how about you tell us the difference between a mile on a FE, and a mile on a RE. Because we know a mile on a RE, but your claim implies a FE mile is SO DIFFERENT as to make a RE distance meaningless on a FE.

[inquisitive]

Interestingly enough, GPS calculates speed through the Doppler shift effect when triangulating location.  A ping from 3 different locations are sent out at regular intervals and the shift in relation to those 3 points is used to calculate speed.

Unless someone wants to deny the existence of electromagnetic wave structure, then both GPS and Radar measure the same physics phenomenon and are both tested using metered tracks and stopwatches.

If that is how speeds are calculated, then that means that the GPS speed test is invalid in regards to this discussion about the shape of the earth since there is no Round Earth lat/lon speed test to compare it to in order to determine whether the Round Earth lat/lon coordinate system is correct.

What evidence do you actually have to even think lat/lon is incorrect.  How would you prove it, or is this another of your ways of confusing any discussion.  Still waiting to hear what equipment you need to produce your map.