measuring xc courses?

runnerguy wrote:

What's everyone's opinion on measuring a course with a Garmin forerunner 205 or 305?

I have the 305 and have walked and jogged our track and get .99 miles after 4 laps in english and can get 1.6 in metric any day/any direction, wet or dry. For setting up a CC course it's quick and easy and everyone is running the same distance. I have been pleasantly surprised with all of the tests I have done.

Could the Jones Counter fans give me an idea how far off they believe the average 5k road race or high school cross country meet is? I guess a better question to ask is how much off would a good measurer be with a wheel or GPS vs the same measurer using the Jones Counter?

26mi235-

Any chance you would be available Saturday or Sunday afternoon to measure and compare measuring devices at Zimmer? I really would like to check it out for myself before or after the Big Ten Meet.

I have heard rumors about how it was measured and think it would be intersting to look at this course.

Measuring Man wrote:

Could the Jones Counter fans give me an idea how far off they believe the average 5k road race or high school cross country meet is? I guess a better question to ask is how much off would a good measurer be with a wheel or GPS vs the same measurer using the Jones Counter?

This is the key question. Is there a standard for error and have different methods or method/operator combinations ever been tested?

dingle wrote:

Measuring Man wrote:

Could the Jones Counter fans give me an idea how far off they believe the average 5k road race or high school cross country meet is? I guess a better question to ask is how much off would a good measurer be with a wheel or GPS vs the same measurer using the Jones Counter?

This is the key question. Is there a standard for error and have different methods or method/operator combinations ever been tested?

We measurers are always looking for better ways to accurately measure courses (and, of course, to verify that they were measured accurately). Any method that supplants the one using the Jones counter must be easily able to be double-checked.

For example, Cyclocomputers have been tried with many variations, but these suffer from various intractable unreliability problems such as occasional missed revolutions of the wheel. GPS devices have problems when courses have sharp curves, tall buildings, nearby trees or other phenomena that block satellite signals (e.g., solar flares or other magnetic storms). We've also found GPS units to be quite a bit less accurate than a Jones counter (typically off by 1-2%, sometimes more). Lasers take a lot of time, can't cover much distance at a time, and are not usable at all around curves (might as well use tape), but they are useful for measure distances to nearby landmarks such as utility poles and sewer grates, where undulations are usually not present and the distances are short.

Any method that is going to supplant the Jones counter (now the Jones-Riegel counter) method merely has to show that it is better.

XC courses are notoriously hard to measure with a wheel of any type because of the typical undulations caused by things such as switching from grass to dirt or vice-versa. The error would vary depending on the number of undulations encountered.

But, you wanted some examples. Here's one. I remeasured a local '5K' that some 3rd and 4th year med school students had traced out with a measuring wheel they had owed. They were only off by a little over 213 feet...

In your example - what would YOU expect to be off from your Jones Counter 5k if you had to use a quality continuos gear metric wheel? 213 feet is almost 70 meters and that seems very extreme. I think I could jog a course off of feel and be closer than that!

Measuring Man wrote:

In your example - what would YOU expect to be off from your Jones Counter 5k if you had to use a quality continuos gear metric wheel? 213 feet is almost 70 meters and that seems very extreme. I think I could jog a course off of feel and be closer than that!

But I AM using a 'quality continuous gear metric wheel' - it's called a calibrated bicycle with Jones-Riegel counter.

If I were using a simple push wheel that was in contact with the ground at all times, I'd still need to calibrate it before and after, and then I'd likely have to walk it through the course, which is often quite difficult to do accurately because of parked cars, dogs, traffic, rocks, etc. I'd expect to get significantly larger errors from one measurement to the next, but I have not tested this.

The biggest problem with pushing a wheel is this: For a road course, this would be MUCH more dangerous that using a bike, because we frequently have to cross multiple lanes of a roadway to traverse a diagonal path.

The second biggest problem with pushing a wheel is that it takes longer than by using the bicycle/counter method. I can easily average 10-12 mph while riding a straight line on the bike and, if conditions are favorable, can often exceed 16mph. I doubt that I could ever exceed 3 mph while pushing a wheel, and would frequently be forced to go much slower.

The 3rd biggest problem with pushing a wheel is that it takes much longer to correct a mistake. For example, if I ride a little past an intended mark, I can carefully back up on the bicycle to the point indicated by the counter. Or, if I get interrupted during a segment and have to remeasure it, it does not take very long to ride back to the last mark and continue forward from there. With a wheel, this would be a challenge.

I post under the same name on the track and field news board - send me a PM there. I will see what my schedule is for Saturday.

By the way, the Southwest Bike Path starting by the stadium is a good place to calibrate a wheel. We used it some years back to set up the 10k course to go along with the marathon. By the way, the marathon markings that go up every year seem to be a little longer than any other metric I have seen, from my bike meters to the posts laid out by the track club to the dots put on by the XC/track coaches at UW (when we did the course, we used a wheel and found that calibration to be off consistently by a fraction of a percent).

This article is timely considering this thread:

http://www.hamptonrockfest.com/hamptonhalf-GPS.html

Keith

Great article!

I would love to post it on my website.

Do you know how I can contact the author?

David

David Katz wrote:

Keith

Great article!

I would love to post it on my website.

Do you know how I can contact the author?

David

Sorry, just the messenger, someone sent it to me that wasn't the author. I'd recommend contacting the webmaster where it was posted.

Nice link Stone!! Sometimes I think you are allright...

In case any of you posting here are unaware let me post this about our fellow poster David Katz

http://www.flrrt.com/london2012.htm

keep the garmin in your pocket wrote:

Nice link Stone!! Sometimes I think you are allright...

As long as it doesn't get out of hand...

In case any of you posting here are unaware let me post this about our fellow poster David Katz

http://www.flrrt.com/london2012.htm

I should also mention that folks that are interested in following the antics of the geeks of measurement (and many other records / race administration areas) you can watch the RRTC (Road Running Technical Council) boards.

Wow! I feel completely the opposite as you on all accounts.

The simple push wheel that I have has a continous gear mechanism that measures forward and backwards at 1/10 of a meter. I check it for kicks, but no calibration has been needed. I can walk with it and jog with it and no calculations are needed to locate k marks or miles. It has a kickstand so it stays exactly where it is when I stop and mark the course. Is it as precise as the Jones Counter - maybe, maybe not. I would be surprised if there was much of a difference and have yet to see the variation with the push wheel as I had with my Jones Counter. Maybe I'm a freak and can push a wheel straighter and navigate corners cleaner with my wheel than I could with my bike.

Keith Stone wrote:

This article is timely considering this thread:

http://www.hamptonrockfest.com/hamptonhalf-GPS.html

The author of that article makes the same mistake that most people do when giving his reasons for why GPS devices can't possibly be accurate at measuring distances. He either believes that 3-10 meter error of the GPS is random error, or he doesn't understand the difference between random error and bias.

The truth is that most of that 3-10 meter error is bias, not random. And bias error has no effect on calculating distance of a GPS path. The definition of bias is that it is the same for all data points. It's pretty easy to understand that if all the points in your GPS path have exactly the same error shift, that error won't change the distance calculation. People need to stop throwing out this 3-10 meter error number. It is irrelavent for calculating distance.

How do I know most of the 3-10 meter error is bias? Two reasons:

1) Take a look at one of your GPS tracks. Do you see consecutive points in the track moving 3-10 meters side to side, or anything close to that? Of course you don't. You might see yourself 3-4 meters offset from a sidewalk you know you ran on, but all the points are that far off the sidewalk in the same direction (bias error). You don't see one point on one side of the sidewalk and the next on the other side (random error). Of course, if you are in an area with tall buildings, all bets are off. In that case, the tracks are usually nuts, as are the distance calculations.

2) People love to theorize why GPS devices should or should not be able to make accurate distance calculations. I didn't bother with the theorizing. I just tested my GPS device.

http://measure.infopop.cc/eve/forums/a/tpc/f/89510622/m/8301003542

So why do people in races with GPS devices get a distance reading that is very different from the USATF certified distance? Very simple. They don't follow the shortest possible route (SPR). And they don't follow it by a lot. It has almost nothing to do with the accuracy of their GPS. How do I know this? You guessed it.

http://measure.infopop.cc/eve/forums/a/tpc/f/89510622/m/9611072113

David Katz wrote:

Keith

Great article!

David

Agreed, good article. At the other site Keith put up, the USATF RRTC site, we had a lengthy discussion about GPS and how to answer to the public a few years back. In short, we all agreed GPS was good but not as accurate as our tools and if called upon, we'd provide explanations to anybody that asked vs come up w/a 'position statement'.

Measuring Man wrote:

Could the Jones Counter fans give me an idea how far off they believe the average 5k road race or high school cross country meet is? I guess a better question to ask is how much off would a good measurer be with a wheel or GPS vs the same measurer using the Jones Counter?

There's no such thing as an 'average 5 km road race or high school cross country' course, thus making a good reply impossible. Nobody has measured a large sampling of non-Jones counter measured road courses to come up w/an average and the accuracy of cross country courses is even further in doubt and the reason this thread exists. I can tell you that 95+% of courses I measure w/the Jones counter are initially laid out short by the host race committee...one by one tenth mile for a 5 km.

Second question would be a bunch of guess work but it's safe to say 95+% of all measuring wheel & GPS measured courses are short. By how much they're short would qualify as 'guess work' as samples would vary.

Thanks "keep the garmin in your pocket"

I'm just a nerd who cares about getting it right. I think I got these appointments because I have been around longer then most - my birthstone is lava!