Power Kite Forum

using GPS for speed records

Scudley - 16-11-2011 at 11:57 AM

Here are a couple of academic papers on the use of GPS for establishing speed records. These are not for the mathematically challenged. One is 9 pages the other 29 pages.
http://www.google.ca/url?sa=t&rct=j&q=use%20of%20gps...

http://www.google.ca/url?sa=t&rct=j&q=use%20of%20gps...

indigo_wolf - 16-11-2011 at 12:36 PM

Quote:
Originally posted by Scudley
These are not for the mathematically challenged.


x approaches infinity, where x = understatement :lol:

ATB,
Sam

BeamerBob - 16-11-2011 at 03:47 PM

I'm not even going to look. Can someone give the Short version? My gps has never given me a reading that didn't make sense to how the run felt. I have a very high level of confidence in it's readings.

RedSky - 16-11-2011 at 07:12 PM

Both links are for the 9 page version. Not that I want to read the 29 page version.

I tested my Garman eTrex H against two cars I've owned in the past 6 months and each came within a maximum of 2mph outside the GPS at 60mph. I was curious as how accurate the car speedometer was.

My friend has an iphone app that allows him to get 70mph by walking down to the bottom of his garden, but I think the phones work differently.

I noticed that he mentions Sandy Point in Victoria Australia , a popular buggy beach.

John Holgate - 16-11-2011 at 11:52 PM

Quote:

My friend has an iphone app that allows him to get 70mph by walking down to the bottom of his garden, but I think the phones work differently.


Dude, that is one FAST gardener!!

I've checked mine in the car quite a few times and find it quite believable, but I have seen spurious readings on my older magellan PIECE OF GARBAGE (oops, did I type that out loud?) while both in a buggy and in a sailplane. According to the Magellan, I had a top speed of 2000kph in the glider.... and another reading of 35kph in the paddock when I know I was only tootling along at 20 something.

My verdict is: usually reliable but can have the occasional glitch.

Scudley - 17-11-2011 at 09:58 AM

How accurate is the location finding of GPS?
From natural Resources Canada (http://www.geod.nrcan.gc.ca/edu/geod/gps/gps13_e.php) single point measurement is good to about +/- 5m.
How fast is a kite buggy ~ 40m/s.
GPS calculates speed from displacement between locations and time traveled. If measurements are ocurring every second, the distance calculated is about 40m, and because we only know the positions of the two points to +/-5m, +/-10m. That is 25% accuracy on distance. Are you going to base a world records on measurement that are that bad.
Even if your GPS is good to 1m, the speed accuracy is going to be +/-5%.
Given that you know speed to +/-5% is there any difference between 83.1 mph and 85.2 mph. Mathematically speaking there is none as you really no the speed to 1 sig fig.
There is also discussion on how some of the sources of error are environmental which means increasing the number of GPS units does not improve the situation unless the runs are made under the conditions.
This is why the author is suggesting that the doppler shift of carrier frequency is a better source for velocity measurements.
The papers are discussing how to improve these number either by changing the method of measurement (9 page) or by statical analysis of the track data to provide to increase confidence (29 pages).
The nub is that we might as well draw names from a hat as use GPS.
S

Does anyone want the link to the 29 page doc on analysis of GPS data to establish a speed over a distance record?.If you think the 9 page doc is dense math, you don't want to see this one.

jellis - 17-11-2011 at 10:20 AM

So the speed records set to date are incorrect or not valid?

Scudley - 17-11-2011 at 10:30 AM

If you were to use significant figures, the record speed is around 80 or 90 mph. Anybody with a speed in that neighbourhood is a contender. Scientifically, I would have to say the current record is fun, but meaningless. Validity is up to the sporting body.
S

BeamerBob - 17-11-2011 at 11:12 AM

I know that when I'm cruising along and watch my current speed, and I feel an extra pull from the kite, I can watch the speed go up smoothly and predictably to match the extra pull I felt. Likewise, a steady speed across the lakebed, shows a steady speed on the gps. I would think that with all that variability, the speed reading would be erratic all the time. Likewise, even with the electro stuff in a car, the gps will consistently read within a mile or 2 per hour the same as my speedo in the car. I have more confidence in the gps than my car speedo. I just don't see any readings from my gps that make me question its accuracy or reliability. If it did, I wouldn't bother attaching it and would go to a bicycle computer that measures speed with rpm of the wheel/tire considering its circumference.

Scudley - 17-11-2011 at 12:42 PM

Bob, what is positional accuracy of your GPS? To be able to say your max speed is 85.1 mph, your gps is going to have to have positional accuracy to about 6".
Those who are paid to do this crap for a living would say your confidence in your GPS is misplaced.
Sorry, please don't blame me. I feel like I told you there was no Santa.
S
ps Your bike computer, if properly calibrated, is good to about +/-2% or about 10x better than gps.

Stole this from GPS explained.
Accuracy Values by Garmin Receivers
Accuracy of position determination Accuracy of position determination

The declaration of the accuracy by Garmin GPS receivers often leads to confusion. What does it mean if the receiver states an accuracy of 4 m? This readout refers to the so-called 50 % CEP (Circular Error Probable). This means that 50 % of all measurements are within a radius of 4 m. On the other hand, 50 % of all measured positions are outside of this radius. Furthermore, 95 % of all measured positions are within a circle of twice this radius and 98.9 % of all positions are within a circle of 2.55 the radius. In the given example, nearly all positions are within circle with a radius of 10 m. The determined position is in the worst case accurate to 10 m.

skelman - 17-11-2011 at 01:08 PM

I'll add my anecdote:

I have a Garmin (GPS) in my car, and usually watch my speed on there instead of my speedometer. I know while accelerating, I've seen my speed on the GPS jump erratically both high and low of what my actual speed is (comparing it to my speedometer). I'm not sure how it compares when cruising simply because I'm not watching the speed on the GPS very often with the cruise control set.

More information is always better imo.

Even though it may be a bit of a buzz-kill for people who use GPS to track speed records, it's worthwhile to know how accurate they actually are.

Scudley - 17-11-2011 at 01:29 PM

Maybe they need to change the output display from that precise "83.2 mph" to "Hmmm, I reckon 'bout 80".
You still need to be going damn fast to get that reading in the 80s.
S

popeyethewelder - 17-11-2011 at 02:00 PM

Quote:
Originally posted by Scudley
Maybe they need to change the output display from that precise "83.2 mph" to "Hmmm, I reckon 'bout 80".
You still need to be going damn fast to get that reading in the 80s.
S


He was...and we as a buggying community trust the accuracy of our GPS devises

vwbrian - 17-11-2011 at 02:08 PM

I think there was 3 + gps's attached to one buggy and all read the same top speed. Maybe we should try multi brand gps to compare accuracy.

BeamerBob - 17-11-2011 at 02:10 PM

Oh Scudley, no shooting of the messenger here, its just that my observations make it seem much more accurate than that. I will admit I've never had a max speed reading over 80 mph............... Yet. :ninja:

greasehopper - 17-11-2011 at 06:03 PM

Who cares ? I've seen speeding tickets beaten down with math too.

It's an exercise for braggin' rights. Very precious, highly dangerous to achieve, life-long pursuit, summiting Everest, Holy Grail kinda braggin' rights. It's "extraordinary", meaning most of us will never see it. It is a gauge for those who keep score. "Lead Dog" is very special and the skill, talent and giant nards required to achieve it in this game are worthy of the highest praise and admiration on any scale.

I happen to like this scale because it's cheap and accessible. If you're looking for accurate, go to Elmer's during speed week and try run the lights with the 200mph cars. Now THAT's internationally recognized accuracy... unless there's a lawyer in the crowd who specializes in beating traffic tickets.

Scudley - 17-11-2011 at 07:11 PM

Quote:
Originally posted by popeyethewelder
He was...and we as a buggying community trust the accuracy of our GPS devises


RYFM and check the specs Popeye. You will see your trust is misplaced. Sorry to pee on the parade.

S

greasehopper - 17-11-2011 at 07:53 PM

And another country heard from...

Thanks for tearing down my illusions and exposing the sham that is wind power sport as measured by a de-funked and egregiously flawed globular possibility simplex. Thank GOD we don't use GPS for commercial Naval, Aviation or Land navigation.

By the way, what it your suggestion to resolve the problem ?

My suggestion... There ARE other windmills to tilt at. Now would be a good time to saddle up and ride out, big boy.

Scudley - 17-11-2011 at 08:21 PM

greasehopper,
all I can say is read the paper. The link is at the top. If you have a problem with his work let him know.
GPS is in used the fields you list for position, not speed, and they do not use it for speed for the reasons listed.
Tell us your gps model and we check the specs and go over the math to calulate the speed and the error.
Now would be a good time to read the paper, big boy.
Then time to put up or shut up.
S

greasehopper - 17-11-2011 at 08:40 PM

Yeah, I read it and I get the joke. My point is, who cares ? I certainly have no need to pick fly poo from pepper. It's "ball park" close, internationally available and CHEAP.

I noticed you presented no reasonable solution to this supposed "problem". I suppose one might deduce an ingenious plan to market a "certified" speedo system is afoot. Outstanding !!! Drive On !!! Best of luck, let me know how that works out. I doubt us "also rans" will be stepping up to the counter but I don't doubt there's a market out there.

Scudley - 17-11-2011 at 08:55 PM

98% confidence on speed of 85.2mph +/-50%
25% confidence on speed of 85.2mph +/-10%

Big ball park.
If you want, we can set pi equal three cause it's easier.
S

greasehopper - 17-11-2011 at 09:13 PM

Okay, last time, I promise.

I'm not trying to be an arse here. A cynic, perhaps, but not an arse.

My point is, we can point to the flaws all day but, in the absence of superior means, it still rules the day.

Who cares how bad it is on paper if it's the smartest choice going ?

What is your suggestion for fixing the problem of the grossly inaccurate ground speed indication of GPS ?

Scudley - 17-11-2011 at 09:55 PM

You did not read the paper, or if you did you did not understand any of it, as it was a suggestion as to how to fix the problem using available technology.
Bike computer is a quarter the price and can be 10x as accurate so GPS is not smartest or cheapest- but GPS is so sexy.
Well if you want to know if one guy is really faster than another, GPS does not rule the day unless one guy is going less than half the speed of the other.
The guy who wrote the paper was concerned about measuring boat speeds, so hopefully the much larger marine market will come up something soon.
I am really sorry the news has upset you so much. Please do not be pissed off with me cause I told you about the problem, take it up with Garmin or whoever it was that sold you something that does not do what you thought it did.
I really look forward to seeing my critics provide the accuracy of their GPS so we can go over the numbers together and see whether the numbers are any better than I say they are.
Afterward maybe the group can come up with a means to measure buggy speed which is reasonable and acceptable to us all.

S

pyro22487 - 18-11-2011 at 02:17 AM

I was curious about this a few years ago when hunting. Using a gps that was accurate to about 250 feet. If the readings are done out of a circle I get the problem. There is no easy fix and also using several gps and getting an average is about as good as it can get. setting up a section of a track and doing a precision time run would be about the best we could do. Problem then becomes how do you aline the track with the wind.... Maybe a laser gun like police use or how they check baseballs being thrown....I agree the system isn't perfect but Its close very close.

I am not picking sides but am curious as to what people can come up with to maybe counter the problem.

csa_deadon - 18-11-2011 at 04:04 AM

The bottom line is not whether or not GPS is "this accurate, or that accurate".

Currently it is the chosen method to validate speeds. Not raining on Scudley either.
But it will take a whole lot of convincing to change the entire buggy community. Not saying that, that is what Scudley was/is trying to accomplish.

Thing to remember, keep in mind is how is any tech evaluated/calibrated and do you trust it?
Remember for years speed was measured by how many times a crude gear went round and round.

:D

RedSky - 18-11-2011 at 04:54 AM

No one has mentioned the accuracy of a paper written in 2007 by a college boy. If it were published in the New Scientist magazine then fair enough.

csa_deadon - 18-11-2011 at 05:15 AM

Something else to consider. Change never occurs based on one paper. Typically a theorem needs to be tested multiple times before it becomes a postulate.

The paper does show promise. For some reason I understood about 75% of what the author was saying. However I do have one problem with one reference site the author used. Wikipedia? Almost all major universities have stated that Wikipedia is not a reputable reference site since anyone can log in and put their two cents in with out a shred of truth to what they are citing.

Having said that, it will be interesting to see where this goes.

Scudley - 18-11-2011 at 06:47 AM

Why has no one sent in the specs of their GPS? Is it because it is as bad as I say?
Wake me up when someone sends in their GPS unit's specs.
S

Scudley - 18-11-2011 at 07:25 AM

Quote:
Originally posted by csa_deadon
However I do have one problem with one reference site the author used. Wikipedia? Almost all major universities have stated that Wikipedia is not a reputable reference site since anyone can log in and put their two cents in with out a shred of truth to what they are citing.


Thank you Sean for having read the paper.
He cited wikipedia as source for definition of Margin of Error and Central Limit Theorem. AFIK neither article is subject of raging controversy. It is common cite such a source as it means everyone is singing from the same page.

the 29 page papers info. do a google search and it will turn up:
SURVEYORS, GPS AND THE
WORLD SAILING SPEED RECORD
R.E. Deakin, W.N. Cameron, D.M. Sil#@%$#! and K. Zhang
Department of Geospatial Science
RMIT University
GPO Box 2476V
MELBOURNE VIC 3001
I got a headache when they started integrating vector cross products

For those did not bother to down load the 9 page paper here is the intro.


Abstract.
This article demonstrates that speed
measurement with accuracy approaching 0.01
knot is possible by using GPS Doppler data.
The method is illustrated with measurements
made by GT-11 GPS unit made by Locosys.
Introduction
Typical approach to using GPS for speed
measurement today is to consider a series of
“trackpoints” that record position estimates
(latitude and longitude) determined by the
GPS at regular time intervals.
Each GPS trackpoint is determined with some
error that is variable and difficult to
determine. Hence, speed values computed
from a series of trackpoints have unknown
accuracy and cannot be considered reliable. It
is virtually impossible to prove the accuracy
of speed computed from a recorded series of
trackpoints.
Modern GPS devices implement digital PLL
(phase-lock loop) receivers to continuously
track carrier frequencies of a number of
satellites. For example, GT-11 tracks carrier
frequencies of up to 12 satellites
simultaneously. The frequency tracking has to
be continuous simply because each receiver
has to be always ready to receive data from its
satellite.
The very fact that data is read from any given
satellite is proof that its carrier frequency is
tracked with high accuracy.
The difference between the known satellite
carrier frequency and the frequency
determined at the receiver is known as a
“Doppler shift”. This Doppler shift is directly
proportional to velocity of the receiver along
the direction to the satellite, regardless of the
distance to this satellite.
The most inaccurate is the method that tries to With multiple satellites tracked it is possible
estimate an average speed over some to determine the 3D velocity vector of the
“accumulated distance” between trackpoints. receiver. In general, the more satellites are
Due to trackpoint inaccuracies, the line tracked – the better the speed estimate.
connecting all track points is a zig-zag, even
if the real path of a speed competitor is a
smooth or straight line. Since the length of
this zig-zag is always longer than a
smooth/straight line, the “average speed”
determined with the “accumulated distance”
method always overestimates the real speed.
The less accurate are trackpoints (the less
accurate is a GPS unit) – the larger the
estimated “average” speed and the more
impressive is the “achievement”...
Doppler
An alternative to measuring speed from series
of trackpoints is using the Doppler effect.

krumly - 18-11-2011 at 08:56 AM

Does this mean everyone who won a beanie or some other swag during the Kitestorm Speed Rankings has to surrender their winnings? (Bummer on them shutting down).

Scudley's points seem reasonable. If folks want to make some sort of 'Official, Guinness BooS-P-A-M-L-I-N-K- sort of claim for a speed record, then there should be a means of validating the claim to a verifiable degree of accuracy and precision. The difference between two contending speeds would have to fall outside the margin of error of the measuring system in order for one to 'officially' be deemed faster than the other. I didn't have to read the paper to figure that's what he's getting at.

And all the folks in the 70-80 mph range on buggy or skis with a kite? I'll never come close, but I'd love to watch them go head-to-head!

krumly

BeamerBob - 18-11-2011 at 10:40 AM

SOMEONE WAKE SCUDLEY UP! Lol.

Ok, I looked up the specs on my Delorme PN-20 gps. For what it's worth, the specs state

WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position

GPS accuracy:
» Position: < 15 meters, 95% typical*
» Velocity: 0.05 meter/sec steady state (translates to about .11 mph)

WAAS accuracy:
» Position: < 3 meters, 95% typical*

So what can we glean from this?

John Holgate - 18-11-2011 at 04:17 PM

Quote:

means to measure buggy speed which is reasonable and acceptable to us all.


I think if we took a vote, GPS would indeed by a 'reasonable and acceptable' measure of buggy speed to 99 odd percent of us.

Would I trust one to save my life if I got lost....absolutely.

Do I believe the speed shown on the GPS is completely accurate? No, of course not. But most of the time, it's close enough.

Will it affect the size of my grin while buggying? HELL NO!!

And the size of my grin when buggying is THE most important thing:smilegrin:

greasehopper - 18-11-2011 at 09:13 PM

Quote:
Originally posted by Scudley
You did not read the paper, or if you did you did not understand any of it, as it was a suggestion as to how to fix the problem using available technology.
Bike computer is a quarter the price and can be 10x as accurate so GPS is not smartest or cheapest- but GPS is so sexy.
Well if you want to know if one guy is really faster than another, GPS does not rule the day unless one guy is going less than half the speed of the other.
The guy who wrote the paper was concerned about measuring boat speeds, so hopefully the much larger marine market will come up something soon.
I am really sorry the news has upset you so much. Please do not be pissed off with me cause I told you about the problem, take it up with Garmin or whoever it was that sold you something that does not do what you thought it did.
I really look forward to seeing my critics provide the accuracy of their GPS so we can go over the numbers together and see whether the numbers are any better than I say they are.
Afterward maybe the group can come up with a means to measure buggy speed which is reasonable and acceptable to us all.

S


Okay, you win. I'm an illiterate, silly, Red Nek. GPS is a sham and I am lying to myself in believing it is anything more than a gross indication of relative movement. Thanks so much for setting me straight on the folly of my ways. I feel enriched and enlightened for it.

Right, now, off ya go...

krumly - 19-11-2011 at 10:31 AM

I started thinking about this a bit more after reading the article Scudley references. It appears the author, Tom J. Chalko, has a a Masters of Science and PhD in engineering. The article makes sense to me. Unfortunately his credentials aren't helped by the rest of the new-age, quasi-science on his website: http://nujournal.net/

But the order-of-magnitude difference in accuracy for speed measurements using Doppler Shift GPS vs trackpoint calculations seems obvious, and has apparently been of interest for verifying high speed sailing and speedsurfing records. See for instance http://www.gps-results.com/GPS_Speed.pdf and the other artciles referenced therein.

GPS receivers record position, time, and other NMEA data depending on brand and model. The sampling rate for the data depends on brand and model, but 1Hz and 5Hz are typical rates (1x or 5x per second). Velocity calculations are performed within the receiver, using brand-specific algorithms. Standard GPS position fixes are accurate within 10-15 meters (33-49 feet). DGPS can increase accuracy to 3-5 meters (10-16 feet). WAAS should enable sub-3 meter accuracy. My guess is most of the buggy or kite skiing fixes we are discussing are standard GPS accuracy. Say your GPS receiver samples position fixes at 1 Hz. At a true 70 mph, you will have covered 103 feet in a second. If your fix is accurate to 15 meters, or 49 feet, an 'instantaneous' speed calculation based on only those two waypoints could theoretically be as low as 54 fps, or 37 mph; and as high as 152 fps, or 103 mph. Interestingly, since velocity is deduced from position fixes, the slower you are going the more error there can be in an instantaneous velocity calculation.

BeamerBob's last post mentioned his DeLorme pn-20 specs as:

WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position

GPS accuracy:
» Position: < 15 meters, 95% typical*
» Velocity: 0.05 meter/sec steady state (translates to about .11 mph)

WAAS accuracy:
» Position: < 3 meters, 95% typical*

What can we glean from this? Firstly, WAAS enabled doesn't guarantee WAAS accuracy. WAAS works only in North America, and I've spent plenty of time in Northern MN and WI where it isn't working on my Etex Vista. Secondly, there is no confidence interval for the claimed margin of error for velocity measurement. A 95% confidence interval is a generally accepted statistical standard of certainty. It could be anything here. Lastly, the claim for velocity accuracy is for 'steady-state' conditions - not instantaneous, which is what where I'd bet a number of speed bursts displayed on GPS receiver displays fall.

I don't know how each GPS receiver is calculating and displaying velocity information, but it seems to me if you really want to be concerned with accuracy and record setting, then you need to level the playing field with consistent data gathering and agreement on a common equipment set-up. It appears that using GPS receivers with a high sample rate that record NMEA Doppler-shift time data in their sample streams, and post-processing the data through a common software method would guarantee this accuracy. Some of this post processing software was pointed out in PetriL's thread 'Speed results from Finland, some new records?' (http://www.powerkiteforum.com/viewthread.php?tid=17292). Picking a GPS receiver that does this internally and displays the speed might be a solution, but it would be wrong to assume the majority of units do this.

Bragging rights using a photo of a GPS display works for me. Just don't expect it to hold up in court, or the Guiness Book if that's where you want to see it.

krumly

BeamerBob - 19-11-2011 at 11:08 AM

If I increase my personal best, all that matters to me is my personal achievement and recognition among my peers. This has me thinking of moving my bike computer over to the buggy for verification. If someday it all came together and I broke Arie's record (don't laugh! :rolleyes: ) , I would want my peers and I to have confidence that I really did it. Using 2 technologies might be just the verification to have confidence in the numbers. As stated above, I think my gps does a fantastic job, since I would scrutinize any number that didn't "feel" correct. I've never had a number that wasn't legitimate based on the feel of the run. If anything, I've had runs that felt faster than the reading gave me. This is interesting to talk about for sure.

snowspider - 19-11-2011 at 06:10 PM

Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game!
PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph

BeamerBob - 19-11-2011 at 09:43 PM

Quote:
Originally posted by snowspider
Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game!
PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph


Based on the purported accuracy of my gps, you would only be off by .055 mph (at 50 mph) worst case so you don't have to sell all your equipment!

greasehopper - 20-11-2011 at 02:29 PM

Quote:
Originally posted by BeamerBob
Quote:
Originally posted by snowspider
Do the papers indicate any software that the gps' use to subtract the average additional zigzag distance and thus arrive at a more accurate speed guestimate. I dont mind getting up to 50.11mph to brag about doing 50 but if I have to crank it up to 52mph I'm getting out of the game!
PB 47.8 on ice, snowspider kitesled, 5m HQ apexII. See if you can beat that you other kitesleders! + or - 0.11mph


Based on the purported accuracy of my gps, you would only be off by .055 mph (at 50 mph) worst case so you don't have to sell all your equipment!


Thanks Bob, that's my point exactly. Although I was not aware that WAAS was not available world wide (because I lead a sheltered life these days) and in spite of the fact I can see where that alone might raise an eyebrow here or there, the question is purely academic. One would have to have something far greater at stake than bragging rights to invest in emerging technology for the sole purpose of recording top speed on a freakin' kite buggy. Guinness is one thing. A community of solid people, many of whom I would routinely stick my hand in fire for... I would expect better of them for no other reason than personal integrity. "Gear" ain't gonna make that happen.

If you can't trust yourself, who are ya gonna trust, a pile of silicon and solder ? Really ?

Sand-Yeti - 20-11-2011 at 10:11 PM

I've owned several GPS's since I started using them back in 1996
2 X Magellans were like house bricks and very slow but always good to navigate even though back then the accuracy was good to within 70 to 100 metres. (frequently better than my navigating with a compass) That was due to the US government back then having a random screw up (security) system on the satellites to prevent accurate readings. Paranoia on terrorrism was prevalent even 20 years ago & not without good reason as we susbesquently learned..

2 X Garmin II+ these were the first GPS's that I could easily upload & download on the PC. I used the first Fugawi software for that. These were accurate on speed etc. Their triangular shaped body made for more complicated fixing on the buggy downtube.

1 X Garmin Geko.
Neat mini GPS that gave good readings but the display actually died from being shaken around too much in the buggy.

3 X Garmin Etrexes. These have been excellent except for one that I think has developed a problem. I buggied just a few hundred metres & it read 475 kms (definitely suitable for dropping dead in the desert). The speed looked to be working accurately though.
One of them has had a tough time with the black rubber band around it peeling and a button fell off. I fixed that by trimming a small pencil eraser, poking it in the hole and then sticking the thing together with contact glue, additional bits of old inner tube rubber, electrical & Scotch tape. It's my favourite GPS & still use it today although my kiting buddies look at me in disgust when I fix this tatty looking GPS to my buggy.

They are all accurate on speed, as they all read the same in the car and the same as the Satnav that I keep permanently in the car. My car speedo reads 5 kph more when I'm driving at 100 kph. l checked several cars and noticed that all car speedos run faster than the true ground speed.

The only thing that I don't depend on are the altitude readings. I find these are way out. I have a separate altimeter that is good to about +/- 2 metres. This works on an atmospheric pressure, so it is important to always adjust it at a known height or known pressure to be confident of its accuracy.

ripsessionkites - 21-11-2011 at 01:52 AM

WTF is this about GPS.
Basically anyone that has their GPS ranking on PTW is all false? hard to believe.

so what if the accuracy is out by a few, you look at the top 10 buggy speed pilots and speed pilots from other sections of kiting (snow/ice). we didn't get here by looking at our GPS to figure out how fast we went. the world record was done with 4 GPS, and two different models from Garmin.
we went out at the perfect time, in the highest of winds, and went for it. not many can say that.

so when you're passing cars on the highway at NABX its a whole new experience and feeling.

SCREW the technical talk ... just ride.

RonH - 21-11-2011 at 06:54 PM

Quote:

SCREW the technical talk ... just ride.


Best advise yet - /End of thread

ChrisH - 21-11-2011 at 08:04 PM

I'm am completely new to this sport and I'm not even thinking about speed records but here is my 2 cents....

There may be only 10 top buggy riders now but when there are a hundred and the top two are only seperated by a couple 10ths of a mph, you will want to know your exact speed. At least I would. Who cares if it's Guinness or any other record book that it might be in, if it's the top speed in the sport it should be exact, in my opinion.

If you're not going for a world speed record then who cares if it's off a little bit, it's just for your own records and those, for me anyway, don't have to be exact. It's just a general idea of how fast I'm going, that's all I need to know for now.

Just my .02, please don't be angered by my opinion.

Scudley - 21-11-2011 at 11:07 PM

Quote:
Originally posted by BeamerBob
SOMEONE WAKE SCUDLEY UP! Lol.

Ok, I looked up the specs on my Delorme PN-20 gps. For what it's worth, the specs state

WAAS-enabled, 12 parallel channel GPS receiver continuously tracks and uses up to 12 satellites to compute and update your position

GPS accuracy:
» Position: < 15 meters, 95% typical*
» Velocity: 0.05 meter/sec steady state (translates to about .11 mph)

WAAS accuracy:
» Position: < 3 meters, 95% typical*

So what can we glean from this?


If you are taking readings every 1 second, a 95% confidence means on average 3 readings every minute have are off by more than 3m.
We are not making a steady state measurement.
I would have more confidence in these reads if people used the data logger functions and recorded their track. At least that way we could see that in the seconds before and after their record max speeds were reasonably consistant. No kind of official record keeping body would accept records consisting of photos of the digital readout.
They would probably want to see some kind proof the equipment was calibrated and working properly. It might be nice to have a half hour of stationary data readings logged at 1 s intervals to ensure that the velocity reads zero when it is not moving taken before and after the
the record. It would also be nice to see that your readings were taking place where you were buggying.
Rather than putting multiple gps on the buggy it would probably be wiser to put two on the buggy and have the others stationary at locations on the perimeter of the flying to ensure that all signals are good over the area.

A pictures of the gps max speed display are cute but leave little to confirm the data is valid.

In most other sailing speed records the use a trap for speed they are not concerned about the alignment of the trap except the tack should be relatively perpendicular to wind. I think their attitude is that if you can't steer your boat so you go through trap straight, you're not much of a sailor.
The other possibility is that for a long time in sailing, speed only counted if it was in the direction you wanted to go.

If you want to be known as the "World Record" holder, I think you have to at least provide the documentation that would satisfy the requirements of high school science lab.

S

RedSky - 22-11-2011 at 06:39 AM

Agreed.
A proper world record attempt as in speed sailing a need for a strict set of guidelines would be called for. Otherwise anyone could get in their car and record a record breaking speed on their handheld GPS, but for us buggiers it's just a bit of fun. Highly addictive fun! :D

In my experience, if the surface you're riding on is hard and smooth, the wind consistent and you're using a performance kite in a well sorted buggy AND you're going absolutely flat out, then you can expect no more than 2.2 x wind speed.

I've yet to achieve 2.2.

I'd say 2.1 x wind speed is a safe bet in ideal conditions + setup and 2.2 as a maximum when everything comes together at once.

I went out in 54mph gusting to 69mph winds and failed to even get close to 1.3 x wind speed. 69mph should have seen me doing 140mph. lol

A dedicated GPS is more than accurate enough for what we do IMO.

snowspider - 22-11-2011 at 09:34 AM

I know smooth wet ice will produce 30+ mph in winds under 10mph and yet I had to have 30mph winds to get my PB of 47 mph. I think the boys from Belgium got some pretty efficient runs on ice , 3x wind speed. There were some discussions about what speeds you can get out of what winds but there is no doubt ice and wide open spaces certainly make it all possible.

popeyethewelder - 24-11-2011 at 01:00 PM

Quote:
Originally posted by Scudley
Validity is up to the sporting body.
S


You see this is a major problem with being "official" regarding speed records...

Guiness records are done over a certain distance in opposite directions within a given time...

Our sport is so unpredictable it can never be set up, how can you say right get to Ivanpah on 16th Feb 2012 we'll go for the record....and on the day there's a lovely 8mph breeze. Not only that, we do not travel the whole run in a straight line, but more of an "S" shape, so again....validating an "official" speed record is nigh on impossible....

So with that in mind, buggiers as a community are not too fussed about the official side of things, mostly we are all using the same equipment, and if a guy is jumping up and down with a huge grin because he has just broken his personl best at 28mph, then we are all pleased for him and accept his GPS reading. When we are getting up to our world fastes speeds, then extra GPS's are added, just to be sure...and when 3-4 GPS devices all read within a few 10ths, then, quite frankly that is more than plenty good enough.

I haven't read the paper nor intend to waste my time on it....I am just more than happy to go with the flow.

Scudley - 29-11-2011 at 07:23 AM

Quote:
Originally posted by popeyethewelder
You see this is a major problem with being "official" regarding speed records...

Guiness records are done over a certain distance in opposite directions within a given time...

Our sport is so unpredictable it can never be set up, how can you say right get to Ivanpah on 16th Feb 2012 we'll go for the record....and on the day there's a lovely 8mph breeze. Not only that, we do not travel the whole run in a straight line, but more of an "S" shape, so again....validating an "official" speed record is nigh on impossible....

So with that in mind, buggiers as a community are not too fussed about the official side of things, mostly we are all using the same equipment, and if a guy is jumping up and down with a huge grin because he has just broken his personl best at 28mph, then we are all pleased for him and accept his GPS reading. When we are getting up to our world fastes speeds, then extra GPS's are added, just to be sure...and when 3-4 GPS devices all read within a few 10ths, then, quite frankly that is more than plenty good enough.

I haven't read the paper nor intend to waste my time on it....I am just more than happy to go with the flow.


It is funny that all other sailing sports have the same problems and are able to deal with them.
I do not have a problem with reporting PB's with GPS, but I think the "world record" needs a little better documentation than a picture of gps units with a max speed displayed.

S

popeyethewelder - 29-11-2011 at 08:11 AM

It is there has to be witnesses,

BeamerBob - 29-11-2011 at 08:21 AM

I tried to mount my bike computer on the buggy and without epoxying the pickup unit to the fork, I can't get it on there. I guess if the wind is high enough to make it a "special" day, I'll strap on a second gps.

Bladerunner - 29-11-2011 at 06:54 PM

Quote:
Originally posted by Scudley
Quote:
Originally posted by popeyethewelder



I do not have a problem with reporting PB's with GPS, but I think the "world record" needs a little better documentation than a picture of gps units with a max speed displayed.

S



If somebody was making or losing big $$ over portions of a mile per hour I could understand you having a "problem " with how it was established . Fact is it isn't the America's Cup, just a bunch of buggy nuts chasing after bragging rights and maybe some sponsorship. Mostly a bunch of Euro's who could care less if you have a problem with their numbers. Fact is they don't care if you have a problem with their methods and neither do the greatest majority of the rest of the buggy world.