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Steve
Phlogiston Purveyor



Joined: 29 Jan 2002
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Steve
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PostMon Feb 04, 2002 7:42 am 
I recently bought a copy of Delorme TopoUSA 3.0 and have since found that the trails are not that accurate and are usually shorter than the green trails maps. One glaring problem I found was the PCT section from Stevens pass to Snoqualmie. The topo program showed the trail to be 51.24 miles in length whereas it is actually about 67 miles. I took a cloder look and noticed that the topo program ignores switchbacks quite often and tends to draw straight lines in areas where switchbacks should be. My question is; Is there a program that has accurate trail data that also has the ability to upload it to 3rd party gps receivers? Thanks,

Despair is only for those who see the end beyond all doubt.
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PostMon Feb 04, 2002 10:27 am 

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Steve
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Steve
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PostTue Feb 05, 2002 8:17 am 
That does help. I've checked out topo! before but decided on TopoUSA since it was only $40 at Costco. I knew before I bought it that it wasn't a great program but the price was right.

Despair is only for those who see the end beyond all doubt.
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Newt
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PostTue Feb 05, 2002 6:20 pm 
Are you sure it doesn't take into consideration elevation? I have Topo 3D WA and if I view the profile and slide the curser up and down it will also show the position on the trail. Seems like if it could generate the profile it would be accounted for. I haven't ever measures anything to see how accurate it is. NN confused.gif

It's pretty safe to say that if we take all of man kinds accumulated knowledge, we still don't know everything. So, I hope you understand why I don't believe you know everything. But then again, maybe you do.
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Map Lover
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PostTue Feb 05, 2002 7:07 pm 
I'm not sure if it's the hypotenuse of the horiz/vert triangle or the various wiggles of wandering outdoors, but the mileage is off by quite a bit on Topo! compared to Greentrails. I assume the Greentrails were measured by wheel by the Forest Service? Also the elev gain is often off by a bit. I think again it's the accumulation of errors in their elevation database.

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PostTue Feb 05, 2002 8:01 pm 

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Newt
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PostTue Feb 05, 2002 8:05 pm 
I just checked the DeLorme site and it says you can measure both terrain and horizontal distance. I'm not sure that Green Trails is wheeled by the Forest Service. Also how did you get the distance/elevation from Green Trails? They got a CD now? Or am I missing something? http://www.delorme.com/quads/features.htm NN confused.gif

It's pretty safe to say that if we take all of man kinds accumulated knowledge, we still don't know everything. So, I hope you understand why I don't believe you know everything. But then again, maybe you do.
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Scrooge
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Scrooge
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PostTue Feb 05, 2002 8:07 pm 
TOPO is always short on distance and always over on total elevation change. Apparently two things happen. When we draw our routes on the map, most of our lines are chords rather than the complex curves of the real trail/route, so what gets measured is a series of shortcuts. By the same token, our chords move up and down between contour intervals much more abruply than the real trails change elevation (even though intuitively it might seem that the real trail would be "bumpier"). Since TOPO interpolates elevations between contour intervals, you get a bunch of extra plusses and minuses added to your trip total. Overall, TOPO is still the most accurate tool available. All you can do is learn to add 10% to the distances and subtract 15% from the elevations, or whatever works for you, and go with it. Obviously, if you're going offtrail all you can get is a general indication, anyway. Odds are your real distance travelled and elevation gained will be substantially more than the program results.

Something lost behind the ranges. Lost and waiting for you....... Go and find it. Go!
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Benjamin
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PostTue Feb 05, 2002 8:20 pm 
2drx, after drawing your 1.64 mile route up Mt. Si, then make the elevation profile for it. Though the two routes are the same length on a map the route up Si is shown as 1.78 miles on the elevation profile. Do the same for the flat route. It stays the same.

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PostTue Feb 05, 2002 8:41 pm 

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Map Lover
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PostTue Feb 05, 2002 10:32 pm 
Greentrails lists mileage on the maps. I presume they got it from Forest Service data, but just a guess.

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Brian Curtis
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Joined: 16 Dec 2001
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Brian Curtis
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PostWed Feb 06, 2002 12:29 am 
TOPO (an other mapping software) uses USGS DEMs to determine the elevation. The DEMs are grids of elevation points with a point every 5 meters. They normally do pretty well, but in some situations they can get completely messed up. The most obvious case are lakes that are tilted. Virtually all are this way. The most extreme example I've seen was a route I traced where we had gone along a knife edge ridge. It extremely steep and the data points were off the ridge such that they added a couple thousand vertical feet to our trip total.

that elitist from silverdale wanted to tell me that all carnes are bad--Studebaker Hoch
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kleet
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Joined: 06 Feb 2002
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kleet
meat tornado
PostThu Feb 07, 2002 12:50 pm 
I am a cartographer, so forgive my lengthy reply... First of all, not all trails CAN be shown. The photographs used for compiling quad maps are captured at a flying height of 20,000 feet above mean terrain, so not all features can be seen. Trails shown are very approximate. There are over 1400 quad maps for Washington alone and only so much time and money available to re-fly and re-map. Trails like the PCT are rerouted more often than the maps are updated. The elevation data (displayed on the toolbar and used in generating profiles) is separate from the information present on the map itself. This elevation data comes from a database of elevation readings compiled by the USGS at 100 meter intervals across the terrain (I’m not sure where the 5 meter figure came from). Using these readings as a guide, it’s possible to interpolate between points, thereby giving a general indication of the shape of the terrain. In the years since these companies first started producing USGS Topo CDs, higher-resolution elevation data has become available. With Enhanced Digital Elevation Data, (which I believe is sampled at 30 meter intervals) the accuracy of profiles and spot elevation estimates is greatly improved. You may be able to contact the company you bought it from and purchase this enhanced data. As far as horizontal accuracy, National Map Accuracy Standards state that 90% of horizontal positions shall be within 40 feet (1/50 of an inch at 1:24000 scale) A DEM (digital elevation model) with the same area coverage must have a root-mean-square error in elevation no greater than 7 meters (about 23 feet). eek.gif Probably a lot more than you ever cared to know!

A fuxk, why do I not give one?
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PostThu Feb 07, 2002 8:31 pm 

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Malachai Constant
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Malachai Constant
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PostThu Feb 07, 2002 10:59 pm 
I till think oziexplorer with CD's burn't from http://duff.geology.washington.edu/data/raster/drg/ have the best combo of detail and value. biggrin.gif I just tested and 13 sec. to download Enchantment Lakes 7.5 min quad. agree.gif

"You do not laugh when you look at the mountains, or when you look at the sea." Lafcadio Hearn
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