Measurement down and across a 4-lane Road

quote:

So, I am thinking I might should just ride on same side for the full length of the 800 meter stretch and then carry bike to opposite side to continue measurement.
The road appears to be fairly straight for the full length of the 800 meters.

What you are thinking of doing is exactly what I would do. It's got several names - "carry-over," "offset maneuver" etc.

If the inaccuracy bothers you, you can always measure the length along one side, and the width, and calculate the diagonal.

Hi Ken,

That "Offset Maneuver" is indeed the preferred method, and is described in Appendix A of our manual, viewable online at http://www.usatf.org/events/courses/certification/manual/appendix-a.asp

From your map, the course appears to be essentially the same as course OK05010BB with map viewable at http://www.usatf.org/events/courses/maps/showMap.asp?courseID=OK05010BB (course measured by Don Garrett while I was OK certifier). Has there been some construction? Anyway, it's good to see that you're measuring again!

Incidentally, by checking it in Google Earth, that stretch of NW 63rd appears to be around 1200 m long, and its width only about 17 m, so the difference between measuring along one edge and the diagonal is only about 0.12 m.

****That "Offset Maneuver" is indeed the preferred method, and is described in Appendix A of our manual, viewable online ****at http://www.usatf.org/events/courses/certification/manual/appendix-a.asp


Pete/Bob – thanks for taking time to respond.



****From your map, the course appears to be essentially the same as course OK05010BB with map viewable at ****http://www.usatf.org/events/courses/maps/showMap.asp?courseID=OK05010BB (course measured by Don Garrett while I was OK ****certifier). Has there been some construction?

Same course, no construction but the race committee asked Don to re-measure the course.



****Anyway, it's good to see that you're measuring again!

After purchase of Kerr-McGee by Anadarko Petroleum, I spent a year working in Texas for Anadarko before retiring in November,2007. My wife and I live in Norman. I now have time to help with course measurements as needed.
Also working on getting back into running and participating in races.

****Incidentally, by checking it in Google Earth, that stretch of NW 63rd appears to be around 1200 m long, and its width ****only about 17 m, so the difference between measuring along one edge and the diagonal is only about 0.12 m.

I was thinking in metrics but the map I was looking at was statue. So the "800 meters" I used in my calculations was actually .8 miles which would be the 1,200 meters as you indicated. Another example of why it is good to have a second person reviewing your work.


Ken Hardwick
Norman, Ok

Ken,

It's curious that the race committee asked for a remeasurement even though there's no change in the course, no construction, and the certification is only a couple of years old. Might they have asked for this remeasurement because runners were complaining the course to be inaccurate based on data from GPS units the runners were wearing? In any case, it's evident that you carried a GPS device while measuring, as your map on the MotionBased site includes GPS data that you uploaded. I notice that you rode the course from Finish to Start, as we often do while measuring. On that MotionBased map, we can see where you did the offset maneuver (near Avalon Ln). Your path doesn't seem to align perfectly with the roads, but I assume that's due to imperfect match of the GPS coordinates and data in Google Maps. I assume that in addition to carrying this GPS device, you also did a standard calibrated bike measurement with Jones counter. Thus, your data contributes to the growing body of comparisons of GPS with calibrated bike measurements, as illustrated by other threads on this board such as https://measure.infopop.cc/eve/forums/a/tpc/f/89510622/m/8301003542

Incidentally, while your data on the MotionBased site is displayed initially in Imperial units, there's a "Switch to metric" button near the upper right (Curiously, even after switching to metric, Elevation is still displayed in feet, although Elevation gain and loss are displayed in meters; also, an incorrect symbol is displayed for kilometers per hour -- should be km/h, not kph).

After switching that display to metric, you can verify the length of the stretch on NW 63rd (a little over 1.2 km) from your GPS data.

The total length of the course was 5.06 km according to the GPS. I assume that the course measured a standard 5 km by calibrated bike (5.005 km including SCPF). Thus, the GPS measurement would appear to be about 55 m greater than calibrated bike. However, the GPS measurement includes the width of the street where you did the offset manueuver (about 17 m estimated by Google Earth), so this should be subtracted from the GPS figure. This reduces the discrepancy between GPS and calibrated bike to around 35 to 40 meters, or 0.7 to 0.8 percent.

Other contributors to the difference between the Jones measurement and the GPS measurement could be the following:

1) If the bike was ever backed up during the ride the Jones would count negative meters while the GPS would count positive.

2) If there were other places on the course, in addition to the offset maneuver, where the Jones was frozen while the bike was moved.

3) If the GPS was attached to Ken rather than the bike, and he got off the bike to do something at some point during the ride.

Because all of these things that we often do during course measurements will mess up a GPS measurement, even if it was perfectly accurate it wouldn't be very practical for measuring courses for certification.

Bob,

I haven't re-measured the course yet. But since I was in the area and needed to get my daily run in, I ran the course so that I would have a better feel of the layout of the course. In fact, when I ran from start to finish, I missed getting on the North-East divided portion of Grand Blvd. So, was glad I did that while on a training run rather than while measuring the course. I now have a better feel for the traffic volumn and street layout so should be able to do a better job of measuring this course.

Ken