Off-trail, UTM, GPS 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

CAUTION: Because I took many (most?) 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 was error inherent in what was done when the GPS signals were deliberately degraded.

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?).


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 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.

Some perspective on personal GPS since I started this hobby (new section as of 11/25/06)

Wow! That pretty much sums it up. My first GPS was a Garmin GPS40 which I purchased from Cabela's Bargain Cave. That unit took 45 minutes to initialize the first time at the store. It took a long time to find itself anytime and was very poor under trees. It probably had a defective receiver and when combined with the 8 channel scanning type acquisition method it meant that you could NOT move under trees because if it didn't see the satellite on a particular scan then it got lost pretty quickly. Plus there really weren't all that many satellites in the constellation yet. My next unit was a Garmin GPS45 with a detachable antenna. It still processed by scanning but the receiver was much better and being able to put the antenna on a suction cup on the windshield really helped get the trailhead fix.  I still haul this unit along on business trips out of habit.Next unit was a Garmin GPS12XL. Oh boy! 12 channels all receiving at once meant that moving thru trees wasn't the problem it was before because the unit was tracking satellites it could see even when others were occluded briefly. I still use this unit most of the time for trips. I like the easy user interface for entering names of waypoints and I've had so much good experience that this unit is "old faithful." And then the govt turned off the deliberate degradation of the fix quality ("SA"). Wow again!

When I was unemployed in 2001 my former co-workers put together a gift certificate  for a local outdoors store which I turned into a Garmin eTrex. The eTrex is a wonderful package in that it has the same size LCD display as the others but in a much smaller case and only requires 2 AA batteries. But I don't get along with it quite so well. The waypoint naming method and waypoint list management is not nearly as handy as in the 40/45/12. But for a super light unit which can do 12 channel parallel fixes it's excellent. I used it on searches for the Larkspur B-17 but found that the waypoint naming was so clumsy that I reverted to old faithful.

Recently in outings with the Colorado Aviation Historical Society I've used my set of Motorola Talkabout FRS radios. As a group we've found that as the search line spreads out, having radios is really handy for group plan changes and for reporting finds. (You'll also read about how important the Talkabouts were in the Mt. Cirrus F-100 group hike.)After selling the Unimog I had some "toy money" so I bought a Garmin RINO110 and a Garmin RINO 130. These units have even better GPS performance plus they have integrated into the case an FRS radio. And they have memory. So- after having resisted using PC interface to my GPS units for so long I now have Garmin's MapSource and have downloaded all my GPS waypoints and remaining tracks and have uploaded maps into the RINOs. The mapping software means that I can clear a GPS of waypoints and tracks and routes and then re-load it for each trip. This also will make the eTrex more useful since I can pre-load waypoints and only have to manually load a few along the way.

The current GPS satellite constellation is very dense. The number of satellites now means that you ought to be able to receive about 7 at nearly all times and this renders an awesomely accurate fix. The RINO 130 has a real magnetic compass as well as a real barometric pressure altimeter.  The altimeter doesn't seem like something so automatically wonderful just yet but the mag compass means that I won't be fiddling with my manual compass after getting a GPS fix and then a bearing to the next point. I'll still carry the mag compass and a map but GPS is making it really, really easy to navigate.

You'll note that all my units are Garmin. I started with them and have found no reason to try anything else. I'm sure that Magellan and Lowrance make good GPS units too. But I'm just too grumpy to learn a different human interface if I don't have to.

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:

Home Moggie!  

Last Modified: 1/1/2008