mlct

Does anyone know what precision AIM stores lap times at? A friend of mine and I are both at 2.02.409 when we look at our best Watkins Glen laps in the data. Our cameras had different settings so showed 2.02.40 vs 2.02.41. Is there a way to show more digits in the data analysis?

Thanks

ProCoach

Hahaha! I think so. In the device config for the logger, I believe, but not on the camera.

awew911

Bigger question, is how does AIM get timing? Since it is by GPS position relative to known Start/Finish line, then that's where the accuracy begins.

If AIM's GPS receiver is 10Hz, then that is your accuracy and moving to higher precision doesn't make your time more accurate.

For AIM GPS based timing, I just use tenths of a second.

Matt Romanowski

A guy like Roger can answer better than me, but it's more accurate than the 10 hz GPS by itself. They use the accelerometers to interpolate position in-between measurements. I'd say it's normally accurate to the hundredths, but that is also dependent on the accuracy of the timing loop to the GPS start finish.

T&T Racing

Does it really matter, just asking?

awew911

Which is why in our DE Cup Championship Series, we only go to the tenths of a second.

ProCoach

That's why I was laughing at the original post. One logger rounds up, one logger rounds down. I'd swap, if I were him.

Matt Romanowski

I don't think he was talking about a logger going up or down, I think he's talking about the data having 3 decimal places and the SCHD video having 2. You'll see the same variance in numbers from the data to the video in RPM, speed, and lap time. It's due to the rounding and info processing for the video.

I've had long talks about the data handling with the Italians about this.

ProCoach

Well, I'd want the "faster" camera, if I were the guy with the "slower" camera! Hahahaha!

mlct

Thanks all. A great point about GPS accuracy that had not occurred to me.

I did have the "faster camera" but the data shows a tie and Luigi's lap came first so I believe he is "ahead". We will have to settle this next year as we shoot for the sub two minute GTB1 guys.

Mark

rbahr

Hi All,

GPS time is a surprisingly complex subject. To begin with, time is a byproduct from providing position. Your time accuracy maxes out at your accuracy (ft or meters) divided by speed of light - figure 1 ft = 1ns. Sooooo if you have 20 ft accuracy you are looking at 20ns time accuracy. That said, GPS position information (from the satellites) is at a 1Hz update rate. Anything better is a result of interpolation in the form of (usually) Kalman filtering and partial updates AND your local oscillator. It can be quite good, but depends on the implementation. Then there is the reporting and time-stamping - If you are using Linux as an OS (which I am pretty sure AIM does) then 1 ms latency is as good as it gets ( I am making some assumptions here).

Bottom line is that without properly designed equipment 1ms accuracy starts to get a bit iffy...

Ray

ProCoach

I think your assumptions are mistaken. When I look at the testing and validation equipment of major OEM manufacturers (Porsche, among them), it’s quite good.

Here’s some good information by a company that has been building signal generators for GPS device calibration (including military) since 1991.

https://www.vboxautomotive.co.uk/ind...cy#gps-factors

ProCoach

Then, there is the etesta upgrade to the MoTeC GPS-L10 with test results here: http://etesta.com/new/new-gpsl20-20h...for-motec.html

ProCoach

And the daddy, the RaceGrade true 20 Hz sampling unit. Good explanations in the manual: http://racegrade.com/downloads/RG_MA...S%20Manual.pdf

Of course, Race Technology offers a 20 Hz GPS upgrade for their DL1, the older VBOX Sport is at 20 Hz and the automotive testing equipment Racelogic supplies the OEM’s (at a not inconsiderable price tag) is at 100 Hz.

More than anything, my experience is that comparable data overlaid from the same equipment is useful. Between different makes/models/specifications, not so much.

rbahr

My understanding of GPS is based on having worked with it directly - folks in my place of work pretty much invented it - no kidding. My understanding of Linux and it's limitations are also after many years of experience with it. Very little if any of what I said was an assumption.

I did say .

Without actually testing this equipment in a lab, my opinion is that one should assume some degree of error in the Ms value. Remember that a good rule of thumb is that your measuring equipment (pretty much irrespective of the technology) should be 10x better than the values you are trying to measure...

I did look at the links you provided - thanks for those. A bit more detail: I was very specific when I was discussing GPS - this is the US version, and there are some number of others - The Brits, Russians, Chinese all have their version, replete with satellites, and very cool math!

The US system provides location 1x a sec - that is it, all you get. You can vastly improve on that with a variety of techniques, but they typically cost $$$, multiple antennas - one of the RT options for their commercial products, multiple constellations - what Motec does, sensor fusion - what everyone does... Books are written about this - got one on my desk - Understanding GPS principals and Applications: Kaplan & Hegarty if you are interested.

And I really apologize if I have taken this thread off topic, was just trying to inform...

Ray