Length of Firewarden's Trail on Mt Hale??

[bobandgeri]

Mohamed

The day we met you on the Fire Wardens trail we had our GPS on - gathering a waypoint every 30 seconds. After downloading to Terrain Navigator Pro - the track showed the traile to be 2.48 miles.

 

[MichaelJ]

The GPS (and your map) gives horizontal distance--the difference between horizontal and 3-D distance is often very small.

On average over a whole hike, sure, but in short segments of ascent it can be significant enough to make my GPS think I'm not even moving, since it calculates velocity based solely on horizontal movement.

However, since I believe trail distances in most texts are also horizontal, not developed, lengths, that would make the GPS match the calculation based on my watch and the book.

 

[bikehikeskifish]

I wonder if the same distance discrepancies (horizontal vs vertical) manifest themselves in software like TOPO, which always seems to underestimate the length of the routes drawn on it. The range is usually about 10-15%.

Anyway, using TOPO, for your loop, Mohammed, and tracing the non-existent trail by copying and old map, I get 17.5 miles and 5300'. The Firewarden's Trail section comes out to about 2.25 miles. Add 10% and you get about 2.5 miles.



(Since I already had this online, I'm assuming I've posted it in another thread already...)

Tim

 

[Zimmer]

However, since I believe trail distances in most texts are also horizontal, not developed, lengths, that would make the GPS match the calculation based on my watch and the book.

I don't think this is true, as in my experience, the GPS varies greatly from the AMC distance on sections with significant pitch, and the AMC distance seems about right based on time, etc.

 

[DougPaul]

On average over a whole hike, sure, but in short segments of ascent it can be significant enough to make my GPS think I'm not even moving, since it calculates velocity based solely on horizontal movement.

For climbs of 1000ft/mi, the difference between horizontal distance and 3D distance is ~2% and for 2000ft/mi ~8%.

If you are moving slowly enough, the GPS cannot distinguish between your motion and the random motion due to position drift.

Also when you are on steep terrain, much of the sky is blocked and accuracy would suffer.

Doug

 

[DougPaul]

I wonder if the same distance discrepancies (horizontal vs vertical) manifest themselves in software like TOPO, which always seems to underestimate the length of the routes drawn on it. The range is usually about 10-15%.

I get a similar discrepancy between WMG and NG TOPO! distances.

Doug

 

[DougPaul]

However, since I believe trail distances in most texts are also horizontal, not developed, lengths, that would make the GPS match the calculation based on my watch and the book.

I don't think this is true, as in my experience, the GPS varies greatly from the AMC distance on sections with significant pitch, and the AMC distance seems about right based on time, etc.

Consumer GPS distances are horizontal.

However, trail distances would depend upon how they are measured.
* A measuring wheel dragged along a trail would measure the 3D distance. But the size of the wheel is a factor--a smaller wheel would measure a longer distance than a larger wheel because it would track smaller bumps and depressions. (This is getting into concepts of fractal dimension and length of a fractal. Same as how long is a coastline?) And how much would the wheel wobble from side to side as a result of the human pulling it following a sequence of good foot placements?
* If measured on a map, one would get a horizontal distance, but what scale map? Does it show every little twist and turn of the trail? (And how accurately is the trail plotted on the map?)
* If measured with a GPS track, you actually have a sequence of points. These points are usually connected with straight lines to create a continuous track. If you are on a perfectly straight route, errors would cause the points to be on one side or the other and lengthen the measured track. If the route curves, the straight lines between the points would cut off parts of the route and shorten the measured track. The magnitude of these effects would be a function of how far apart the points are. (These effects also occur with a survey grade GPS (and traditional surveying), but one would expect that the errors would be smaller.)
* If estimated by hiking speed and time, how did you calibrate your speed? If you calibrated it by hiking trails that are listed as being 10% longer than they really are, then your estimates might average 10% high. If you calibrate and test on trails that have been labeled by the same authority, you have no way of telling what your absolute accuracy is. Also, how consistent are you--is your estimate the same when you are tired, hot, carrying a heavy pack, breaking trail, etc? I'd expect human estimates to be the least accurate method for measuring a trail.

Basically, there is no fundamental length of a trail--the "correct" value depends upon a set of assumptions. And each method of measuring would have its own systematic errors (biases) and random errors.

In other words, all trail lengths are approximate and different sources can legitimately give different numbers.

Doug

 

[RoySwkr]

Gene Daniell says that when he measures with a wheel, he tries to have the wheel follow the actual route a hiker would, wending around obstacles in the trail rather than just the distance of the trail centerline.

Brad Washburn measured the length of the lower Crawford Path with a tape in winter as it was easiest to drag then (it was off his map but he wanted it for a note?), this would be an on-ground distance but shorter than the above.

When my sister does GPS mapping of trails, she makes sure to stand at the end of a switchback for well over the measurement interval to be sure that a point is taken there or otherwise the trail will appear shorter than it is.

 

[dms]

Gene Daniell says that when he measures with a wheel, he tries to have the wheel follow the actual route a hiker would, wending around obstacles in the trail rather than just the distance of the trail centerline.

Gene is fanatical about this approach using his surveyors wheel. Many years ago when I was on the guidebook committe with him, he asked me if I wanted to do a hike with him while he measured a couple of trails. Little did I know what he meant by a couple of trails! We started out on the Kendron Flume Trail to it's junction with the Ethan Pond Trail, we then pushed the wheel out to the Ethan Pond campsite, a couple of backpackers were quite amused by the sight of Gene and his wheel as he pushed right up to the edge of the leanto. Then back on the Ethan Pond Trail to the Zeacliff Trail. While pushing the wheel up Zeacliff, a group of Cub Scouts was descending, I can remember their incredulous looks as Gene pushed the squeaky wheel up some very steep pitches.We then got on the Twinway and wheeled our way out to the summit of Zealand. We then went down to the Zealand Falls Hut, took a short break, and then headed over to the A-Z Trail, we then got on the Willey Range Trail we went up to Tom, and then finally headed back going over Field and Willey. By this time the sun had disappeared, but to this day I can remember the incessant squeaking of the surveyors wheel while descending the slide in total darkness. I believe the total distance was well over 20 mi. We finally got back to my truck by 9:30/10 pm for the long ride home. Such is the dedication of Gene Daniell.

 

[DougPaul]

Gene Daniell says that when he measures with a wheel, he tries to have the wheel follow the actual route a hiker would, wending around obstacles in the trail rather than just the distance of the trail centerline.

I believe that there is also a specified wheel diameter, but different hikers travel slightly different routes.

Brad Washburn measured the length of the lower Crawford Path with a tape in winter as it was easiest to drag then (it was off his map but he wanted it for a note?), this would be an on-ground distance but shorter than the above.

When my sister does GPS mapping of trails, she makes sure to stand at the end of a switchback for well over the measurement interval to be sure that a point is taken there or otherwise the trail will appear shorter than it is.

Sure, you do what you can to minimize the sources of variation. But you cannot eliminate them entirely.

A trail is a complex physical object which does not have an inherently defined exact length. When measuring such an object, one uses a mixture of conventions and procedures to give a useful number with minimum variation.

Making sure you record a trackpoint at the end of each switchback helps, but the effect occurs on any turn or wiggle.

When we did the first GPS bake-off, we had the track set to "auto normal". (One GPS had a different setting which resulted in a much sparser track--we had to elminate it from the comparisons.) I later realized that any auto setting was biased (because it is based, in part, on the track itself) and used time only (30 sec stationary, 5 sec walking, and 1 sec biking) for bake-off #2 to eliminate that source of error.

GPSes have random errors on time scales ranging from days to a fraction of a second. (The formal accuracy spec is based upon a 30 day continuous observation.) There is no way to avoid them with real-time use of a consumer GPS. And, of course, there can be constant systematic errors. The best way to avoid them is with high accuracy commercial surveying gear.

However one does it, it is still a physical measurement of a complex object. One can do one's best to minimize them, but there will always be errors of some magnitude. (In scientific research, one should not only try to make an accurate measurement, one should also estimate the error of that measurement.)

Doug

 

[NH_Mtn_Hiker]

Whatever Doug!

 

[Zimmer]

* If estimated by hiking speed and time, how did you calibrate your speed? If you calibrated it by hiking trails that are listed as being 10% longer than they really are, then your estimates might average 10% high. If you calibrate and test on trails that have been labeled by the same authority, you have no way of telling what your absolute accuracy is. Also, how consistent are you--is your estimate the same when you are tired, hot, carrying a heavy pack, breaking trail, etc? I'd expect human estimates to be the least accurate method for measuring a trail.

I see your point, but I'll reiterate that I'm very, very good at estimating distances while I hike, and when I'm clueless, I know it. At the risk of being run off the board as a nutcase, when I hike solo, I normally have just a small fanny pack with water bottles, and I often jog, keep track mentally of the various milestones (e.g. brook crossing at 0.6, trail junction at 1.0), and yes (here's where you'll send the medics for me, I'm afraid) I sometimes count steps to keep my mind "in the zone", if you will. I'm pretty good at estimating and typically when I'm thinking "the brook must be 100 yards ahead", voila! there it is.

I'm fairly sure that it was on the N. Tripyramid slide that we were noticing the distance discrepancy, and maybe we were suffering from GPS malfunction, but it surely was more than 8% between what the GPS said and what the book said.

 

[dms]

Whatever Doug!

I agree! I'm talking about a guy who busted his ass to put together a guidebook that had as accurate information as he could possibly provide given the equipment he had to work with. Get real!

 

[NewHampshire]

So I guess the answer to Mohameds question would be?????:

No one knows for sure because the tapemeasure Brad Washburn used was made in china where Gene Danielles wheel was clearly a Taiwanese product,and since both obviously vary 2/100ths of an inch this means the totality will be off by a sum greater than the acceptable deviation. And since my stride is bigger than a person of siz 5'4" one can't reliably use the GPS unit because of height descrimination, which is unfair but your GPS is cheaper than mine so na na na naa naa!



Me thinks we are being a bit too uptight and literal. If Mohamed wanted a distance to the nearest micron with ZERO percent error then he would have asked.....well, I guess the only one he COULD ask would be god almighty himself!

Brian

 

[NH_Mtn_Hiker]

...Me thinks we are being a bit too uptight and literal. If Mohamed wanted a distance to the nearest micron with ZERO percent error then he would have asked.....well, I guess the only one he COULD ask would be god almighty himself!

Brian

Weren't you paying attention? I said, 2.5 miles.

 

[Mohamed Ellozy]

Me thinks we are being a bit too uptight and literal. If Mohamed wanted a distance to the nearest micron with ZERO percent error then he would have asked.....well, I guess the only one he COULD ask would be god almighty himself!

Mind you, I asked a fairly simple question. Had I been more with it, I could have asked "How Long is the Coast of Britain?". For a simpler intro to the subject, see this puzzle.

 

[NewHampshire]

Weren't you paying attention? I said, 2.5 miles.

Oops, sorry, I was blinded by the intenses light and booming voice like thunder and rapture

Brian

 

[Double Bow]

I'm glad your '55 guide and my '55 guide agree.

FWIW, my '55 guide agrees as well...

 

[RoySwkr]

I believe that there is also a specified wheel diameter, but different hikers travel slightly different routes.

A trail is a complex physical object which does not have an inherently defined exact length. When measuring such an object, one uses a mixture of conventions and procedures to give a useful number with minimum variation.

A wheel of roughly 3' diameter is often used to measure trails as it rolls over rough objects better than the 8" wheel often used to measure utility locations on pavement. The larger wheel may give a slightly shorter distance on the same track as it rolls up & down over objects.

Take the S Hancock Trail which I just hiked - in the winter you might go up the fall line with crampons and glissade going down and hence travel close to the minimal centerline distance, while in summer you might wend your way up & down taking advantage of various rocks and roots to step on hence travel a longer distance. However your travel speed will probably vary more than the distance travelled.

 

[JohnL]

Is the wheel pushed by an African Swallow or a European Swallow?

JohnL