I could measure a calibration course by steel tape, but I'd prefer to use something electronic, if similarly accurate, for speed and safety reasons.
Are any measurers using a handheld laser measuring device with a target plate (e.g., FatMax, Leica, etc.) for measuring calibration courses? The FatMax TLM 300 is supposedly accurate to about 3/8 inch at 600 feet, but costs between US$350 and $480, depending on the supplier and new vs used.This message has been edited. Last edited by: Alan Avery,
With a helper I can lay out 300 meters in half an hour. Working by myself it still takes less than an hour using a steel tape. It's quick, it's easy, and I already have the equipment. I don't see an advantage in using an electronic rig. You have to pick it up and take it back when you are done, unless you own it. All in all I see no time saved. Granted, the accuracy is slightly better on a level road, but the extra accuracy is not significant. Taping is entirely accurate enough for our purposes. No need to measure with a micrometer if you are going to cut with an axe.This message has been edited. Last edited by: Pete Riegel,
Others have mentioned over the years that they lay out courses solo. I've done it occasionally but am wondering how you and others handle that task. I found it "do-able" but not necessarily easy. Of course it's better to recruit a co-conspirator but sometimes you just need a calibration course and nobody is around . . .
(I reckon this is something else that was in MN and I have forgotten!)
I have tried the methods of Pete and Mike and find them very easy though of course very slow. However, at the risk of sounding like a broken record, I should like to remind you that if you were to adopt pressure monitoring, you would get the best accuracy by using only one calibration course near your home for all your certifications.
The laser measuring devices I mentioned are all handheld units. Using one to measure a level calibration course seems to consist of:
1) Place a target plate perpendicular to the curb at the marked point.
2) Walk, run, or ride to the next read point (100, 200, 500 or 600 feet away).
3) Point the device toward the target plate.
4) Press a button, take the measurement. (may need to adjust position until desired measurement position happens. measurement point is usually the base of the unit, not the end emitting the laser.)
5) Repeat as necessary.
Of course, with 2 target plates and a measurer with 600 foot accuracy, you could drop the 2nd target plate at the 500' mark, then mark the end of a 1000' course quickly. Metric distances can be measured just as quickly. Plus, you can ride your bike to the next read point, and use the bike counter to estimate where that next read point is.
It seems to me this ought to take much less than an hour, you don't need to make a temperature adjustment and you don't need to rewind a tape.
You may need to measure the course endpoints from nearby landmarks using tape, if the landmarks are within a few feet.
Of course, using the laser tool for measuring distances to nearby landmarks for course measurement points would seem to be similarly quick, assuming your target plate is adequately anchored (for me, it always seems that at least one course landmark is further away than the length of my 100' tape). Since these units can remember a set of measurements, you should be able to save a fair amount of time measuring these distances with the device as well.
Hence the reason for my initial post. Anyone have any experience with these devices?
I doubt Alan's proposed method (if indeed he proposes it) is sufficiently accurate for our purposes. My doubt can be disspelled by simply checking. Take readings at the ends of some already-taped calibration courses and see what you get. I'd expect to see average accuracy pretty good, but wide variability.
It's even easier than the above. Just take a single reading at a single spot. Do it each day for a week. See how well the positional readings agree.This message has been edited. Last edited by: Pete Riegel,
Devil's Advocate here.
How can you be sure that the road surface has no undulations? Lay your head on the pavement and see if you can see the other end? That is the only way I can think of, short of pulling a string; but that would require enough tension to break the string, if you got all the sag out. And, if the sag in the road isn't readily apparent, since a slight rise 50' out obscures a sag between 100' and 400', how can you be sure you observed correctly?
So, if there are undulations, the tape method would have a better chance of following them, as it is anchored every 100 feet. A laser doesn't take undulations into account, leading to inaccuracy. While a road may look flat, is it?
Giving the Devil his due:
If a runner can easily jump over the undulations (following the shortest path, of course), which method is better?
If you were measuring a course with a pothole, would you expect the runner following the shortest path to place their foot in the pothole?
Clarifying the Devil; by "undulation", I didn't mean "bump". I had in mind a rolling variance in elevation, measured linearly exceeding 50 feet, and measured altitudinally, varying plus/minus a foot or more.
Some people would notice that undulation, but not everyone. However, it would make a difference in the length of the cal course, since we measure to the fraction of a cm. The laser wouldn't pick up that variance, but a tape would have a better chance, especially if the ends were in the depression.
Even if the tape is longer, undulations are not a problem. When you pull with the correct tension the tape either follows the contour of the road, or it is obvious that it doesn't because it is suspended over the ground. If it is the latter, you need to use shorter tape lengths.
But I still think it would be interesting for someone to do Pete's test with one of these things. I wonder if you can rent one.
I own a Laser Disto A5 which is one of those $450 measuring devices that is also used in track & field measurements. It is capable of measuring up to 200 meters with an accuracy of 50 millimeters (1.9 inches). That would not be accurate enough for calibration course. Even if the Laser Disto were accurate enough for a calibration course, measuring a calibration course with the device is not quite as easy as pointing and clicking.
In order to make a measurement, the unit sends out a laser beam that is reflected off the target and received by the Laser Disto. That works well when the target is a large or the object is nearby. It's a bit tougher to sight smaller targets like a target plate. To help, there is a built in telescope with a four arrows that point to the center. When you sight using the telescope, you can see the red laser beam on the distant targets. Although the beam is visible indoors, it is far more difficult to see in bright sunlight. There are red sunglasses available that may help. As you can imagine, measuring after the sun goes down is actually easier since you can see the red beam.
Another problem is holding the Laser Disto steady. The unit is approximately 6" x 2.5" x 1.5" and there is a tripod mount located approximately 0.5" from the end opposite the lens. Without a tripod, I usually prop the Laser Disto on a something soft like it's case, an eyeglass case, even a shoe. That also keeps the plastic body for getting scratched on the ground. The tripod mount is handy, but you will need a mini-tripod with a wide base (like the bogen-manfrotto model 482).
I included some photos of the Laser Disto.
Laser Disto on a tripod showing the bubble level.
Front of Laser Disto. Note the image at the upper left indicating the tripod was used.
Front end of Laser Disto. The round opening is the telescope.
Side view showing the telescope view finder.
Red dot on the wooden block is the laser pointer.
I would not recommend the Laser Disto as the sole device for measuring a calibration course. The Laser Disto would be better used to quickly measure the details for the start, finish and mile markers. Typically, I place the paint can on the leading edge of a marker. Then I hold the Laser Disto on the utility pole, fire hydrant, etc. and measure the distance to the paint can. It's a lot faster than tape and may help to keep you out of the traffic. -- JustinThis message has been edited. Last edited by: Justin Kuo,
How does one verify the accuracy of the Laser Disto?
One could check the accuracy of a particular hand-held laser measuring device by comparing to steel tape, or by comparing measurements to an electronic distance meter. I'll compare my Leica Laser Disto unit and post those results. That comparison, however, would be from a very small sample and would really only tell us the accuracy of a one laser measuring unit.
This may be beyond the scope of the RRTC, a bit off topic, and perhaps unnecessary but... how does one verify the accuracy of a "calibrated" steel tape? How often should a tape be checked? What is considered an acceptable tolerance?
Issue #111 (January 2002) of Measurement News described an experiment done by Mike Wickiser and Pete Riegel. Thirty-three tapes were compared with one another, and against a tape which had been calibrated at the National Bureau of Standards. The issue of Measurement News #111 may be downloaded at: Tape Comparison.pdf
All the tapes checked out between 99.995 and 100.032 percent of nominal length. As tape manufacture in the US must meet a government standard, the results are not surprising. A 30 meter Brazilian tape, not included in the results, measured to 30.01 meters.
I took the Laser Disto A5 to the track to do some testing this afternoon. I had intended to measure the 100 meter straight, first with the Laser Disto and next with a Pentax Total Station (EDM). The track was partially covered with snow and ice and I had difficulty locating a 20 cm x 10 cm white target with the Laser Disto mounted on the table-top tripod. I may have been able to measure the target at 100 meters if the target was larger or I had used a tripod that raised the Laser Disto a bit higher from the track surface.
There was a trash can located halfway down the track. I taped a standard sheet of paper to the trash can and was able to take measurements with the Laser Disto from the finish line.
Sheet of paper was taped to the target
I set up the Pentax Total Station on a tripod, set it to "reflectorless target" and took three measurements. The horizontal distance measurements were 61.9206, 61.9120 and 61.9080 meters with an average of 61.9135 meters. I placed the Laser Disto and mini-tripod on a case to raise it off the track and aligned the front of the Laser Disto with the plumb line from the Pentax Total Station. The three measurements to the trash can were 61.925, 61.897 and 61.909 meters with an average of 61.910 meters.
Pentax Total Station (EDM) used to measure distance to the trash can
The Laser Disto was just 3.5 millimeters shorter than the Pentax Total Station, or within 0.0057%. (The NIST allows 100 meter steel tapes a tolerance of 0.0083%) I would need to repeat the test but it does appear the Laser Disto had an acceptable accuracy for 60 meters.
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