|
| Another Garmin Rant (Read 662 times) |
| view log |
posted: 2/19/2008 at 4:47 PM |
I have a Forerunner 205 with latest software download. Yesterday I ran 20 laps on a modern, 400-meter track. Garmin showed that I had run 5.3 miles, rather than the 4.9712 (8k) that I actually did. This a staggering 30 seconds per mile at 8-minute pace!
This isn’t the first time I’ve done tests such as this on routes known to be accurate. You say it only does this on curves? Well, the next time you find a race that doesn’t have curves or turns, let me know. And I say this too--if you can't trust it to measure a curve accurately how in the world can you trust it to have pinpoint accuracy (as so many people seem to) on any kind of deviation from a perfectly straight line?
Something to think about for those who say “my Garmin said the course was “xx..x” miles long and then question the course length. I’ll trust a certified course ANY day over a GPS device. This is one reason I don’t really feel comforatable about a PR unless it was run a certified course or track.
I love my Garmin. It’s great for giving me a ballpark figure of how far I’ve run on a strange route and keeping track of a lot of data. However, it has limits. For races I leave at home, preferring to use my trusty stopwatch and mile markers to gauge my pace.
The next time I hear another "but my Garmin said..."
I will..............count to 10  |
Masters PR's:
40's - 5k 16:39; 10k 33:48, 10m 56:25, HM 1:15:27, Marathon 2:43:12
50's - couch potato
60's - 5k 19:00, 10k 38:35, 10m 1:05:30, HM 1:24:09, 30k 2:04:33 |
|
|
| view log |
posted: 2/19/2008 at 5:19 PM |
I have found the courses with tight loops are less accurate. I ran a Half Marathon in Vienna, Austria last year and my Garmin read 13.0. It was a 3 loop course. I recently ran a 5K here in South Carolina and it read just a bit long (3.2 I think).
I've only used it a couple of times on a track and found it will say anything from .23 to .28
When you think about it though, why would you even need it on a track? I use my stopwatch there also, and for any short intervals.
I like to have it for races though, just to help make sure I don't start out too fast. The lap pace (set at 1 mile) gives a pretty good number.
Adjust your expectations accordingly and then I think you'll realize the value of the device....or not 
Steve
|
|
|
| view log Frustrating Project |
posted: 2/19/2008 at 5:37 PM
modified: 2/19/2008 at 5:41 PM |
Well, that's 6.6% high, which is well outside of what you should expect:
GPS Position Accuracy*
<10 meters. 50% typical
GPS Velocity Accuracy*
<0.05 m/s
*Accuracy depends on view of the sky.
99% clear view, 95% typical
Normally, the GPS data sort of self-corrects as you go -- positional inaccuracy is not cumulative, and errors don't compound the way they might with a footpod-based device.
However, since you're running the same "course" over and over again, I think the errors do add up because you're not adding any new data locations. I'll bet if you ran on a certified 8k course, you would probably have much more accurate distance.
Think of it this way. Let's assume you ran a perfectly straight line course that was 8k long, and you had only two GPS points -- start and finish. If the first location was off by 10m, and the last was off by 10m the other way, that's 20m/8000m = 0.25% off.
However, run one lap on a track. If the GPS start location was off by 10m, and the finish by 10 the other way, thats 20/400 = 5% right there. And you're running that loop over and over again.
Bottom line -- I think running on a track is the worst case for a GPS device because positional inaccurately gets magnified by the repetition and there aren't enough unique GPS location points.
As for race courses, assuming clear GPS the whole way, most Garmins will measure long because the runner will most likely not run the perfect tangent lines and tightest possible curves. If a course is certified, the runner should trust the course over the GPS unless there's a gross error (like a 4:40 10th mile after averaging 7:30 the rest of the way). |
20th Century: 800m: 2:04 |1600m: 4:37 |3200m: 10:06 |5k: 16:23 |10k: 35:38 |15k: 54:20
25k: 1:35:59
21st Century: 5k: 19:42 |10k: 43:00
"Do not allow children to mix drinks. It is unseemly, and they use too much vermouth."
Steve Allen |
|
|
| view log |
posted: 2/19/2008 at 5:43 PM |
Quote from sjutton on 2/19/2008 at 5:19 PM:I have found the courses with tight loops are less accurate. I ran a Half Marathon in Vienna, Austria last year and my Garmin read 13.0. It was a 3 loop course. I recently ran a 5K here in South Carolina and it read just a bit long (3.2 I think). I've only used it a couple of times on a track and found it will say anything from .23 to .28 When you think about it though, why would you even need it on a track? I use my stopwatch there also, and for any short intervals. I like to have it for races though, just to help make sure I don't start out too fast. The lap pace (set at 1 mile) gives a pretty good number. Adjust your expectations accordingly and then I think you'll realize the value of the device....or not Steve
I wore the Garmin because I was doing a long workout where I run from the track to a hill, do some hill reps, then back to the track. I wanted an idea of overall distance. While on the track I decided to give Garmin another little test, which I have done before. Normally I use only my stopwatch for track workouts.
As far as adjusting expectations, the reason I did the track test was so that I could make the adjustment. However, when it measures the same 400 meters differently from one time to the next, it is not possible to make an adjustment accurate enough to suit me.
In any case I still like having it but am aware of its limitations.
|
Masters PR's:
40's - 5k 16:39; 10k 33:48, 10m 56:25, HM 1:15:27, Marathon 2:43:12
50's - couch potato
60's - 5k 19:00, 10k 38:35, 10m 1:05:30, HM 1:24:09, 30k 2:04:33 |
|
|
| view log |
posted: 2/19/2008 at 5:46 PM |
| Quote from jEfFgObLuE on 2/19/2008 at 5:37 PM: Well, that's 6.6% high, which is well outside of what you should expect:
Normally, the GPS data sort of self-corrects as you go -- positional inaccuracy is not cumulative, and errors don't compound the way they might with a footpod-based device.
However, since you're running the same "course" over and over again, I think the errors do add up because you're not adding any new data locations. I'll bet if you ran on a certified 8k course, you would probably have much more accurate distance.
Think of it this way. Let's assume you ran a perfectly straight line course that was 8k long, and you had only two GPS points -- start and finish. If the first location was off by 10m, and the last was off by 10m the other way, that's 20m/8000m = 0.25% off.
However, run one lap on a track. If the GPS start location was off by 10m, and the finish by 10 the other way, thats 20/400 = 5% right there. And you're running that loop over and over again.
Bottom line -- I think running on a track is the worst case for a GPS device because positional inaccurately gets magnified by the repetition and there aren't enough unique GPS location points.
As for race courses, assuming clear GPS the whole way, most Garmins will measure long because the runner will most likely not run the perfect tangent lines and tightest possible curves. If a course is certified, the runner should trust the course over the GPS unless there's a gross error (like a 4:40 10th mile after averaging 7:30 the rest of the way).
Interesting. It does seem to do a better job on road courses I've checked. When in doubt, however, I'll always trust a course measured with a Jones counter over one measured with a GPS.
|
Masters PR's:
40's - 5k 16:39; 10k 33:48, 10m 56:25, HM 1:15:27, Marathon 2:43:12
50's - couch potato
60's - 5k 19:00, 10k 38:35, 10m 1:05:30, HM 1:24:09, 30k 2:04:33 |
|
|
| view log Bif! Bam! Pow! |
posted: 2/19/2008 at 5:54 PM
modified: 2/19/2008 at 5:55 PM |
I have never had a certified course be off by anywhere close to that % I wear my garmin for all my races...let me go look up some from last year:
OctPDX marathon: 26.2 measured 26.25 0.2%
Sept5K - 3.1 measured 3.15 1.6%
Sept1/2 M 13.1 measured 12.5 but I lost the signal in the woods several times
July1/2M 13.1 measured 13.1 0%
June 1/2 M 13.1 measured 13.21 0.8%
I think thats enough. I also have Hood to Coast which matched up eeily well, but that isnt certified
When I run on the track I ignore the distance, manually lap and log the intervals. On my track the 1st lane is usually flooded, so I dont have that accurate anyway...someday I'll have to measure lane width to adjust.
MTA - when logging a certified course, I of course always log it by the certified distance not the garmin distance |
Beware the Pink Boxing Gloves of DOOM!
"It's not enough to bash in heads, you've got to bash in minds" - Captain Hammer
2008 Goals New PR's in 5K 10K HM, M What now?
I failed the 12 minute run in 11th grade... |
|
|
| view log formerly RacingThoughts |
posted: 2/19/2008 at 5:58 PM
modified: 2/19/2008 at 6:00 PM |
| Mine was pretty accurate last time I ran on a 400m track, although when I looked at it on a map it was all over the place. I ran in lane 3 or 4 and it was recording .26 miles for every lap. Over 20 laps the .26 reading would have been .2 miles over 8k, which is about right according to this site (http://www.philsport.com/narf/atrack.htm#B, over 20 laps lane 1 = 8K (4.971M), lane 4 = 8.402K (5.221M)). What lane were you running in? I was also running slower than you which could had made it a little more accurate I guess. |
|
|
| view log Frustrating Project |
posted: 2/19/2008 at 6:04 PM |
| Quote from Ennay on 2/19/2008 at 5:54 PM: I have never had a certified course be off by anywhere close to that % I wear my garmin for all my races...let me go look up some from last year:
OctPDX marathon: 26.2 measured 26.25 0.2%
Sept5K - 3.1 measured 3.15 1.6%
Sept1/2 M 13.1 measured 12.5 but I lost the signal in the woods several times
July1/2M 13.1 measured 13.1 0%
June 1/2 M 13.1 measured 13.21 0.8%
That's excellent. You have a very accurate Garmin and/or you run the course very smart for the shortest possible distance. Most folks that I've seen post Garmin distances for race courses end up being a couple tenths long.
|
20th Century: 800m: 2:04 |1600m: 4:37 |3200m: 10:06 |5k: 16:23 |10k: 35:38 |15k: 54:20
25k: 1:35:59
21st Century: 5k: 19:42 |10k: 43:00
"Do not allow children to mix drinks. It is unseemly, and they use too much vermouth."
Steve Allen |
|
|
| view log |
posted: 2/19/2008 at 6:30 PM
modified: 2/19/2008 at 6:31 PM |
It also depends how good of signal/how many satellites it was picking up. My handheld navigational Garmin actually tells you on acquisition what ther +/- error is according to current signal quality; the running versions don't! For example, last time I booted it up I had clear sky and an error margin of 86 feet! The time before it was only 15.
It really irritates me when people wear a GPS on a certified course and then try to complain that the course is off. If you take a GPS run and overlay it onto a map using the software, the results are sometimes quite interesting. You can see that it is clearly not recording your exact route.
GPS has inherent error. Depending on signal, I'm told it averages around +/- 15 FEET. This is why at running speeds the instantaneous pace function is USELESS, the distance you cover between sampling points is too close to the inherent noise generated by the error.
GPS is a good guideline. Take it as that, with it's limitations, and run happy! |
"Talent" is a cop-out for not wanting to try harder.
marathon - 2:28
HM - 1:09:53
10K - 30:57
5K - 15:18 (2nd half of above 10K) |
|
|
| view log Funky Monkey |
posted: 2/19/2008 at 6:32 PM |
| Quote from jEfFgObLuE on 2/19/2008 at 5:37 PM: I think running on a track is the worst case for a GPS device because positional inaccurately gets magnified by the repetition and there aren't enough unique GPS location points.
Actually, with the x05 series, even long nonrepetitive courses can cause problems. The GPS signal tends to track a bit wide of the actual course as you go around tight curves. It seems to measure a wider radius. The track is bad both because of what you have indicated PLUS because it is very curvy and each time you go around the curve you add distance (while if you just did strides back and forth on the 100 m straightaway, you would likely get a pretty accurate reading).
A marathon that runs a long straight line will likely have limited error given good signal, while a very curvy marathon will generally have much greater error. |
| It's all fun and games until the flying monkeys attack. |
|
|
| view log Bif! Bam! Pow! |
posted: 2/19/2008 at 6:40 PM |
| Quote from spaniel on 2/19/2008 at 6:30 PM:
GPS has inherent error. Depending on signal, I'm told it averages around +/- 15 FEET. This is why at running speeds the instantaneous pace function is USELESS, the distance you cover between sampling points is too close to the inherent noise generated by the error.
LOL yeah. I have had my garmin tell me I am "currently" running 4 minute miles. I always keep the mile lap setting on and look at average lap pace.
Jeff - lol Why run farther than I have to!
Actually I had one race where my garmin measured 6.0 for a 10K and I got suspicious, mostly because I live there and run the course often and because I lost the 0.2 all in mile 5. I went home and gmap'd it. 6.0, I got in my car and drove it. 6.0 It was off! And then I ran it again this year and it turns out there was a short out and back segment at one turn that I had missed last year...at least it wasnt a AG award I would feel bad. Although I blame the volunteers for not directing traffic well. |
Beware the Pink Boxing Gloves of DOOM!
"It's not enough to bash in heads, you've got to bash in minds" - Captain Hammer
2008 Goals New PR's in 5K 10K HM, M What now?
I failed the 12 minute run in 11th grade... |
|
|
| view log |
posted: 2/19/2008 at 6:42 PM |
| I was referring to certified courses. I too have run too many community races where it WAS actually off, but I can usually tell from my splits and finish time and not from GPS. Barring an error in direction on race day or mis-marking the start/finish, certified courses are WAY more dependable than GPS. |
"Talent" is a cop-out for not wanting to try harder.
marathon - 2:28
HM - 1:09:53
10K - 30:57
5K - 15:18 (2nd half of above 10K) |
|
|
| view log |
posted: 2/19/2008 at 7:16 PM
modified: 2/19/2008 at 7:16 PM |
I've thus far been awfully impressed with my new 305's accuracy. I ran yesterday on a very hilly, very curvy course with (certified? Trent?) mileage markers ... and it nailed each marker to within a step or two.
Nice to know that it's not completely accurate, though. Because its been telling me that some of my long-time regular runs aren't quiiiiiiite as far as I've been saying. I'm just chalking that up to Garmin error and sticking with my original distances. Stupid Garmin. |
E-mail: JakeKnight2002@aol.com
-----------------------------
|
|
|
| view log Funky Monkey |
posted: 2/19/2008 at 7:36 PM |
| JK. Mile marker 7 is off. |
| It's all fun and games until the flying monkeys attack. |
|
|
| view log |
posted: 2/19/2008 at 7:37 PM |
| Quote from Trent on 2/19/2008 at 7:36 PM: JK. Mile marker 7 is off.
I was in EW not PW. Are they certified over here?
How far off is 7 in PW? That's not the one your kids painted, is it? I'm thinking that's 9. Or 8. |
E-mail: JakeKnight2002@aol.com
-----------------------------
|
|
|
|
|
