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47896Re: GPS Routes

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  • mcooprec
    May 1, 2010
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      For the benefit of people just beginning to learn GPS: elevation readouts on GPS devices are virtually worthless. They are inaccurate on account of physics: it's really difficult to gauge how high something is when viewing it from above, and that is essentially what the GPS satellites do when getting a fix on your position. This is one reason why altimeters are such a valuable navigation tool.

      Altimeters save time and energy when traversing terrain (versus climbing or descending), as they allow you to avoid needless up and down travel when no obstacles are in your way. For example, when traversing around the head of a basin to get to an exit point you've marked on the map or using GPS, an altimeter makes it easy. And finding that hidden lake in deep forest (I'm from Oregon :-) )? An altimeter -- in conjunction with a map bearing before leaving the trail -- is sometimes indispensable.

      Other useful navigation tools include your watch and the sun. Once you've determined your bearing to an intermediate destination, note the position of the sun and what time it is on your watch. Knowing roughly how fast you usually travel carrying a given load, maintain the sun's angle to your bearing and hike just shy of what you think it'll take in minutes to get to the next turn, obstacle or other significant feature along your route. Thus you reduce the need to be constantly taking field bearings and turning on your GPS (draining the batteries) enroute to the next move along your route.

      Thanks for the links, Mohave Ben. Might come in handy next year, if I go somewhere outside of the 5 states I have topo software for.


      --- In Zion_National_Park_Hiking@yahoogroups.com, "mojave_ben" <mojave_ben@...> wrote:
      > Haven't bought a hard copy map in years... Note that the great investigation Ried did (as referenced on the GC group) may be out of date - what's available online now is pretty high res. There's plenty of free services - mapper.acme.com is one I use - that take provide a better user interface to the Terraserver data, but there are some places (northern Death Valley) where the maps are skewed as digitized and there is a bunch of error at the seams. Just find the area you want and print.
      > There was a recent post over at the GC group, I think by Rich Rudrow, giving a URL for the USGS site which now has digital topos online and free.
      > On the GPS thread 1) I've seen someone much more experienced than I make the "wrong datum" error, especially since many GPS units default to the 83 datum and the topos are printed in the NAD27 datum. You also of course really want to learn to use UTM - it's a 1 km grid and in UTM mode the least significant digit on your postion is in meters, so it is close to counting paces.
      > But in any place with high relief, especially Zion canyons, your GPS isn't going to work well. And whatever you do, think about the question, what happens if your GPS dies? Can you still figure out where you are? Simply learning to visualize your position - i.e. visualize the terrain based on the contours - is a skill to develop.
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