This is why language needs to be added like there is with Track & Field from NFHS for records. Yet, I don't feel a steel tape measurement is needed/required for all high school meets, just those where records are claimed.
This is why language needs to be added like there is with Track & Field from NFHS for records. Yet, I don't feel a steel tape measurement is needed/required for all high school meets, just those where records are claimed.
hunt the big game wrote:
You are funny. How about I send you an article that includes various numbers and I allow you to read it once and then I give you a 20 question quiz. The average person like me would get 10 correct, a smart person would get 15, and maybe a smarty pants like you would get 18. That is why I read the article several times. I attended a conference with 1000 coaches after the Garmin meet. Coaches talked about the meet at breaks and in the evening. All coaches accepted the times and distance and were focused on speculating how fast the guys would run in track. Most were predicting 30-40 seconds faster on a track.
Wow! I sure hope you and your coaching friends are right! That would be like 15-28 guys under 14:00,and a bunch in the 13:30s! How many do you think will be below Rupp's 13:37?
hunt the big game wrote:
The GPS measurements were amazingly accurate and consistent. They differed in length based on where the runners ran on the course primarily due to where they were in the pack. You can view measurements from the day prior also for runners when they were able to run closer to the line.
Check this out about how amazingly accurate and consistent these four gps watches were in this test
https://www.youtube.com/watch?v=_px0pNUAeD8&t=189sDiscoGary wrote:
hunt the big game wrote:
The GPS measurements were amazingly accurate and consistent. They differed in length based on where the runners ran on the course primarily due to where they were in the pack. You can view measurements from the day prior also for runners when they were able to run closer to the line.
How do you know they were accurate? You are making the case that they were precise.
I think we need to discuss GPS accuracy versus precision because it looks like GPS precision has improved in the last 15 years and a lot of people are claiming this means the accuracy of GPS measurements is getting better. This is going to be hard to swallow, but depending on the number of turns, the accuracy might be getting worse. In fact, <b>a perfectly precise GPS unit will guarantee an inaccurate measurement on courses with turns!</b> I've tried to avoid this level of detail because without diagrams its hard to explain what's happening, but here goes.
Let's start with 3 basic concepts for GPS measurement.
1. GPS takes location measurements at a specific sampling rate. In many GPS units that sampling rate can be adjusted.
2. GPS measurements have an inherent location uncertainty which introduces location errors for each measurement in a 360 degree circle surrounding the actual location. So the actual location maybe to the side, front, or back of the reported location.
3. GPS calculates the linear distance between two measurements, so error is introduced on turns due to the fact that the turn is truncated. Maybe there are GPS units with curve fitting algorithms, but I am not aware of this. If not, they should be doing it.
So let's do a thought experiment with our perfectly precise GPS unit. On the straights it doesn't matter how fast or slow you go as long as you stay near the SPR your measurement will perfect. So far so good.
Now we get to the turn. The faster we go around the turn the fewer number of sampling points we get and the more truncation will occur, guaranteeing that the course will measure short ... assuming a perfect GPS unit. The only way to get very close to the actual length is to speed up the sampling rate or slow waaaaay down around the turns so that the sampling points are almost on top of each other.
I know what you're thinking. "Thanks Mr. Disco. Will do. I'll be right back." .... Wait!
The problem is that GPS unit are NOT perfectly precise. They do have an inherent location error, and that error can accumulate with each sample so the slower you go the more error will accumulate, unless they are curve fitting, and they might be, but then the curve fitting needs to be checked. So how do you verify the unit is curve fitting?
Glad you asked. You set the unit to its highest sampling rate and go very slowly on a straight path for as long as you can tolerate. Lateral measurement errors should be piling up without curve fitting, making the path seem longer. Then go as fast as you can on the same path. If both measurements come out to within a meter, then the unit must be curve fitting, which means its throwing out distortions caused by lateral measuring errors.
In general a purist won't want to hear that our measuring tool is actively changing measurements along the way to make things come out right, but I'm willing to keep an open mind on this because a very precise GPS unit with a properly calibrated curve fitting algorithm would definitely be "good enough for cross country", and might even be good enough for keeping records. But I gotta see the proofs first, and that means testing the theory against the current gold standard, the tape.
At this point, a whole bunch of the GPS measuring guys should be pulling out that tiny manual that came with it trying to find out if their unit does curve fitting. Let us know.
You also might be thinking that I'm back tracking from the tape measuring push. A little yeah. Because until I started to explain this it hadn't occurred to me that GPS units might be actively trying to remove measuring errors. The more I think about it, the more I think they probably are because the people building these things have to have thought about this, so I really want to see this put to the test.
Ghost of Ward Cleaver wrote:
hunt the big game wrote:
The GPS measurements were amazingly accurate and consistent. They differed in length based on where the runners ran on the course primarily due to where they were in the pack. You can view measurements from the day prior also for runners when they were able to run closer to the line.
Check this out about how amazingly accurate and consistent these four gps watches were in this test
https://www.youtube.com/watch?v=_px0pNUAeD8&t=189s
Great! That video demonstrates everything I was trying to get across. The sampling rate is about 1 second. You can see the linear paths between measuring points, and the truncation on the turns. We see no evidence of curve fitting on any of these paths. We see that all units do not have the same precision, because some are 12 meters away from others, so some of the units are too far off for our purposes. Based on what I saw in this video I would not accept a "national record" based on a measurement by any of these units, but I'm keeping my mind open.
Yeah, I believe gps watches have made a lot of progress but still have some issues. Sounds like there are some versions that use an algorithm on tracks to do a better job with the curves. Looking forward to testing some of those watches.
Ghost of Ward Cleaver wrote:
Yeah, I believe gps watches have made a lot of progress but still have some issues. Sounds like there are some versions that use an algorithm on tracks to do a better job with the curves. Looking forward to testing some of those watches.
The blue apple watch line is promising, but would need more investigation.
Fun fact: GPS units would be useless if their calculations didn't use Einstein's Relativistic equations to account for the differences in speed between the satellites and your location, along with the differences in the strength of gravity due to the distance of the satellite from earth. And he came up with the Theory of Relativity without any empirical data, just thought experiments because relativistic effects were so small that there was no way to confirm it until they found a way to verify it by measuring light bending during an eclipse. Einstein was the man.
DiscoGary wrote:
Ghost of Ward Cleaver wrote:
Yeah, I believe gps watches have made a lot of progress but still have some issues. Sounds like there are some versions that use an algorithm on tracks to do a better job with the curves. Looking forward to testing some of those watches.
The blue apple watch line is promising, but would need more investigation.
The irony since Apple Watch GPS is about the least accurate thing out there. You want some extra distance on your run then wear an Apple Watch. It would probably measure RunningLane at about 3.25 miles.
coachy wrote:
DiscoGary wrote:
The blue apple watch line is promising, but would need more investigation.
The irony since Apple Watch GPS is about the least accurate thing out there. You want some extra distance on your run then wear an Apple Watch. It would probably measure RunningLane at about 3.25 miles.
It sure seemed to be the line following the path the closest in that video! That's why all the claims about GPS need to be double checked.
Yep, and crazy how far off the two Garmins were.
Coachy, just think how far off a CC course would be if someone used that apple watch you mentioned and called it good at 3.11? Would that even be three miles if the Garmin are all accurate at 3.10, 3.11, 3.12, 3.13, 3.14, 3.15, etc.?
I have run the Spring Lake course many times and my watch always hits the miles spot on.
Ghost of Ward Cleaver wrote:
Yep, and crazy how far off the two Garmins were.
Coachy, just think how far off a CC course would be if someone used that apple watch you mentioned and called it good at 3.11? Would that even be three miles if the Garmin are all accurate at 3.10, 3.11, 3.12, 3.13, 3.14, 3.15, etc.?
I have never claimed that the Apple Watch would be a good measure at RunningLane that's for sure. I don't even let my team use Apple Watch measurements. For those that have an Apple Watch it's actually more accurate just to run the Strava app from their watch.
I am far from the defender for all GPS measurements. I was a Race Director for many years and people would bring me their ONE GPS watch measurements to say that a course was "off" or something. But if you do have 20+ GPS measurements (not on the track) on a course with limited turns, wide open, taking tangents, and no U-turns I think it can be a pretty good measurement for a course.
Agreed. Under those conditions some GPS units would give you a "pretty good" measurement good enough for cross country.
But what if lightning struck and someone ran 14:01 on your "pretty good" 5k course, and everyone around you was clamoring for you to claim a national record had just been set on your course? Based on everything we've discussed, what would you say to them? What would you be doing before you said anything to anyone?
Do you mean if we had engineers lay out a dedicated course several years ago and we wheeled it 100 times since and we wheeled it the day before then and we had hundreds of GPS readings that averaged about 3.115 from that race? I would absolutely proclaim it a national record. Every reasonable person would.
If it was my course I would already know the measurement so I would have no problem declaring it a National Record. I would be celebrating it.
monguse wrote:
Do you mean if we had engineers lay out a dedicated course several years ago and we wheeled it 100 times since and we wheeled it the day before then and we had hundreds of GPS readings that averaged about 3.115 from that race? I would absolutely proclaim it a national record. Every reasonable person would.
A reasonable person might do that, but what would a responsible person do?
The race director is responsible for the race. He is the responsible person and hasn't spoken out since out so the real life answer is that a responsible person would know the course distance ahead of time and declare it a national record. This has already happened. You really seem to struggle with the facts of the situation.
coachy wrote:
DiscoGary wrote:
Agreed. Under those conditions some GPS units would give you a "pretty good" measurement good enough for cross country.
But what if lightning struck and someone ran 14:01 on your "pretty good" 5k course, and everyone around you was clamoring for you to claim a national record had just been set on your course? Based on everything we've discussed, what would you say to them? What would you be doing before you said anything to anyone?
If it was my course I would already know the measurement so I would have no problem declaring it a National Record. I would be celebrating it.
And how would you know? Wheels and GPS?
OK. Let's assume that your wheeled-course record stands and no one questions it. Then a month later the record is broken on another course where the coach says he's "pretty sure" his course is 5k. And he starts celebrating. What do you say then?
monguse wrote:
Do you mean if we had engineers lay out a dedicated course several years ago and we wheeled it 100 times since and we wheeled it the day before then and we had hundreds of GPS readings that averaged about 3.115 from that race? I would absolutely proclaim it a national record. Every reasonable person would.
Any course that had hundreds of GPS readings that average 3.115 miles is most certainly short of 5km. A true 5km XC course will have GPS readings of at least 3.15 miles and usually more than that.
And if your GPS watch hits the "mile" mark spot on every time, it is because the mile mark was measured with a GPS watch.
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