Off-trail, UTM and Cautions

Disclaimer: I assume no responsibility for incorrect coordinates, hazardous conditions between your car and the wreck site or any other hazard you may encounter.  You should be responsible for yourself as you pursue this activity. If you don't know how to go hiking, driving, or walking safely, get professional help. Getting lost in the woods with inadequate gear can be FATAL. If I had a lawyer, he'd probably tell me to never tell anyone about anything.  Be careful!

GPS/equipment & Standard Operating Procedures

• Mark car location before leaving it to hike. I normally have the GPS sitting on the dash of the vehicle and operating from vehicle power as I drive to the trailhead in order that it be tracking satellites and have good nav. data when I am ready to park the car. (It takes 30 minutes of on-time for the GPS unit to collect all the predictive data it will need so as to know what satellites to look for the next time it gets turned on.)
• Mark each significant intersection of trail or terrain for the return trip.(give it a memorable descriptive name)
• Be aware that the GPS requires both clear skies, and good satellite configuration in order to give *any* fix at all.
• Carrying the GPS like a Star Trek Tri-Corder is pretty much a waste of time, energy and batteries. I may use it to help me find my way to a pre-entered set of coordinates to begin searching but I use it in short sessions. I might walk for an hour then bring out the GPS to see where I need to go . I will then put it back and use my hand-held compass to keep me going in the right direction.
• The GPS does NOT know what direction it is facing unless it is moving faster than about 3 mph and is receiving good info from satellites. You MUST use a compass in conjunction with the GPS. (Very, very new models might have genuine compass capability by now. Read your owner's manual.)
• Coordinates listed here are mostly "pre-SA off." SA stands for Selective Availability. This was a deliberate ‘dithering’ of the signals coming from the satellites done by the Department of Defense in order to confuse the very precise position that would otherwise be generated. In my coordinates, allegedly there is a 95% chance that you are within 100m of the correct position. After the dithering was stopped in 1999, GPS coordinates are within about 15m accuracy using ordinary commercial quality units.

CAUTION: Because I took coordinates pre-SA shutdown, you still must use descriptive information provided when trying to find the wrecksites listed. One hiker reported being on the wrong side of the ridge from the Crown Point B-17 when using my coordinates. I'm sorry about that but there is error inherent in what we're trying to do here.

UTM  and Datum Discussion

There are some additional nuances about GPS that should be discussed. Most consumer-grade GPS units have the capability of handling alternative coordinate systems and alternative datum (plural?).

UTM

The most useful alternative coordinate system is UTM. UTM stands for Universal Transverse Mercator. That's nice. This doesn't explain why it's useful. In a nutshell, it is useful because it is a decimal-based system which allows you to very accurately transfer coordinates to and from your USGS quad map.

Consider the problem of trying to plot coordinates in a degrees, minutes (that's the  ' symbol) , seconds (the "  symbol) system.  How does one interpolate 40 seconds?  In practice, 40 seconds is 2/3 (or 60%) of the way between minutes.  In UTM, the interpolation is already contained in the coordinates you have.

If you have a modern USGS quad map, you should be able to find tick marks along the edge with a string of numbers - 4130  for instance. If you were to pencil a grid across your map based upon these marks, you would find that you have divided up your map into a series of squares  each 1km (1000meters) on a side. So when you go to plot your coordinate: say 4130600   you would know that this is 600 meters from the edge of the 4130000 line.  Try it on your map and see for yourself. When I'm transferring coordinates to/from my USGS maps I will ONLY USE UTM. It's wonderful!

Datum

Datum is another word for "reference system."  Most consumer GPS units can accomodate different reference systems.  This becomes important in MY coordinates because I do not use the standard WGS83 system that GPS units are normally delivered to initialize with. I use the NAD27 reference system because that's what the UGSG quads use. NAD stands for North America Datum 1927.  Yes, it's old. But it's what the maps use.    This makes transferring coordinates to and from the map more accurate.  It also introduces an error between GPS units operating in WGS83  compared to NAD27.  The magnitude of the error is not known to me at this time.  Be sure you set your GPS to the right datum when using my coordinates. That's why it's part of the table - so you know to think about it.

Note- During a Colorado Aviation Historical Society outing to the Pingree Park B-17 it was found that one of the students had failed to enter the correct datum for the coordinates he was given. He was aware of the datum and had thought he'd used the correct datum but something happened and he did not. While standing at a checkpoint we each compared our GPS readings to that checkpoint. Coordinates were entered the same but the datum was different. His GPS told him that he was 0.15 miles from the point while mine read that we were 0.05 from it (basically within touching distance).  The datum difference at this point yielded a 0.1 mile error in position. That may not sound like much but that difference could be very frustrating in the woods.  The error could be larger. I simply don't know. USE THE CORRECT DATUM!

GPS Decimal

You'll find entries on each crash page labelled as "GPS decimal."  This is my way of having the coordinates available for easy typing into the US Census Tiger Mapserver so that I can construct the link to show the maps.  My Garmin GPS units can easily be changed to show and use UTM,  degrees and decimal degrees, degrees + minutes + seconds and so forth.  If you need to convert from one system to another, do it the easy way, change the display in your GPS and then look at that waypoint again.

Off-Trail Hiking Precautions

Off-trail hiking requires a heightened sense caution which should lead you to exercise greater than normal preparedness. When hiking off-trail you will be less easily found if injured, will not be accidentally found by others in the area and are much more likely to encounter bad footing, down trees or get lost. I've hiked off-trail by myself very happily many times but this might not be for you. All the outdoor wisdom says you should not go alone and indeed this is good advice. I've just found over the years that if I'm not willing to go alone, I might not get to go at all. Still, I work very hard to minimize my risks when I go and I try to pay close attention to each and every move and step I am going to make because breaking a leg  while alone off-trail is a horror scenario.

When hiking off-trail I regard the following as essential:

• A good hiking stick to help with balance.
• Leather gloves to hold onto trees and tree branches for putting them aside.
• Eyeglasses or safety glasses to keep from getting poked in the eye.
• A boonie hat to help route branches and twigs away from your forehead and ears.
• Long sleeved shirt or coat for times when you have to press thru heavy brush or tree branches.
• Step OVER logs and not on them. Bark can peel from a log or it can be wet. Place your feet carefully for EVERY step all day long.
• Carry a whistle, firemaking supplies, first aid, and sufficient gear to stay put if you should twist an ankle.
• Tell someone reliable where you have gone, what time to expect you to call them and what to do if you are overdue. Leave them the info in writing so they don't have to rely on memory.
• Have food, water, and clothing to excess. If you are injured and have to spend the night out you will be glad you brought that long underwear top with you. I normally have a fleece jacket and long underwear top to replace a sweaty T-shirt. I also hike in synthetic underwear and avoid heavy cotton such as blue jeans. GOOD raingear (not a cheap pvc poncho) is also helpful for keeping warm if necessary.

Home Moggie!  

Last Modified:7/8/2006