GPS: What do you use, and why?

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 12:25 am

What about reflections and GPS?


I'm glad you brought up this topic.

GPS locations can be degraded if reflected signals are processed as if they were direct signals, because such signals have a longer path-length and travel time, but are assumed to travel directly from the satellite(s). If the unit cannot remove reflections based on polarization of the signal, an inaccuracy may result.

If you carry the GPS on your shoulder, and there is an extremely dense mass nearby, reflections can be a serious problem. So definitely, some people should not use GPS.

Thanks!


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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 12:49 am

I always carry a backup for my harness and ATC, in the form of extra webbing and biners. Should I also have a backup for my GPS?


I'm glad you asked that question. Yes the GPS backup should come in the form of extra batteries and a small but good compass. Of course you have a map, like all good SPers. Try to select a GPS that uses standard AA or AAA batteries (not a proprietary battery, especially not a built-in battery that must be recharged), and carry extra Li-metal batteries. The Li metal batteries have a very long shelf life, are light, and work well in cold. However, check first to see if your unit will accept Li metal; some units are said to work with Li (such as the 60csx), but the batteries must be discharged slightly beforehand, else the new batteries will cause an overvoltage and the unit will shut down.

Another bizarre gaffe is that some GPS manufacturers say the units take Li-ion AA or AAA batteries, when they actually mean Li-metal.

I use a very small sighting compass as backup. The mirror is also useful for signalling, checking contact lenses, and helping Alice Cooper with his makeup.

Thanks in advance!


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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 1:40 am

My hobby involves photographing poops in the outdoors, then returning to the same sites in months or years, to see what has grown on the poops. Can I use a GPS to track the poop locations? I’m particularly interested in poops that are not near readily identifiable trails or features. Will the GPS be accurate enough?


I’m very glad you asked; the answer is not straightforward. I’ll assume that you are mainly concerned with horizontal (x,y) accuracy.

With the new, sensitive chipsets, the absolute accuracy of a hand-held GPS may be as good as +/- 10 feet. With an unobstructed view of the sky, and WAAS activated, the accuracy may be +/- 6 feet. However, many factors can degrade the accuracy. GPS is a tool with limits, and you should be aware of the limits.

First, if the view of the sky is obscured, and the unit sees just a small number of satellites, the accuracy can balloon to hundreds of feet; under dense tree cover, even newer units will typically have an accuracy of +/- 20-50 feet. The signals are microwaves, and the same things that alter or absorb microwaves in your kitchen, will affect the GPS. Clouds, falling rain, and snow generally DO NOT affect the accuracy greatly, as the water droplets are too small and dispersed, and frozen water has a different energy absorption band; but a wet case can significantly reduce the signal. Your head and body are also problematic; the GPS should be as high as possible when carried, and the best signals come when it is held away from you body. As discussed previously, reflections can be a problem, particularly when the unit is a few hundred feet from vertical high walls, or if your head is very dense. (Reflected signals are actually less of a problem if you are right at the wall.) In the worst case I’ve seen, reflections offset the signal by an apparent 100 feet. Always display the estimated accuracy on the GPS, and know the signs of error, such as sudden jags in the track when you have been moving consistently.

In your case, if the poops are not near a distinctive feature, the GPS may get you within 10-20 feet; but that may be a long ways in rough country. You would best photograph the poops or perhaps draw them in situ (pastel colors preferred), so you can do an exact relocation when you are within the circle of error.

In some places, an error of +/- 10 feet can be a serious problem, so never let the gadget overwhelm your common sense. For example, I often use the GPS to locate complex scrambling routes in Red Rock, NV. A horizontal uncertainty of +/- 10 feet can put me up or down one ledge, and the correct ledge may be 50 feet vertical above or below. If the GPS tells me to step 10 feet to the left, but there is a great big drop there, I’ll send my partner first (see “Plans and Partners: Trusting Types”).

WAAS is more battery-consumptive, and usually works only on fairly elevated terrains, or those with an unobstructed view of the southern sky (strictly speaking, WAAS only works in the US, but Europe and much of the rest of the world has something similar). The WAAS satellites are geosynchronous (and thus above the equator), and are generally not in view if you are in a canyon or north-facing slope. I leave WAAS turned off on my current unit.

I’d like to discuss relative accuracy, vertical accuracy, and time-averaging, areas where a simple GPS can do better, but that will have to another thread.

gosh you are so kind!


Yes, I am.
Last edited by MoapaPk on Wed Jan 14, 2009 1:43 am, edited 1 time in total.

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 1:47 am

goldenhopper wrote: Hey, what happens in PnP stays in PnP. Even our bad grammar! MoapaPk, I thought you stayed out of PnP. Have you been secretly admiring us over there? :wink:


I'm glad you asked.

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woodsxc

 
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by woodsxc » Wed Jan 14, 2009 2:16 am

Dingus Milktoast wrote:
rhyang wrote:
Dingus Milktoast wrote:after I repeatedly invited and was rebuffed by another climber about the same route


I'm kind of expecting an explanation. I told you repeatedly what was going on with me. If you felt 'rebuffed', then I am confused :?

If you had mentioned this to me privately, then I could have explained in more detail. But if you are going to slander me in public or tell stories behind my back .. what the hell ?

Oh screw it .. I have plenty of friends to climb with. If you are going to be like this, then have a nice life dude.


To quote aprevious poster:

"
OK, that was a cheap shot "

See when you used THAT example and then added you 'expected' that response?

Oh screw it. I have plenty of friends. If you are going to take cheap shots and then play the holier than thou card you can, have a nice life dude.

DMT


The maturity on both sides here is stunning.

If you want to fight this out to the bitter and unsatisfactory ending, do it elsewhere.

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jrbouldin

 
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by jrbouldin » Wed Jan 14, 2009 3:16 am

Hey Dingus and Rob:

You two are both good guys that contribute to this site and it's just a misunderstanding/misinterpretation perhaps aggravated by having a bad day or life at the moment or whatever. Happens to everyone.

Forget it and let it drop and cool off and don't worry about it.

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 3:37 am

twoshuzz wrote:MoapaPK,

I have the 60SCx. As I've stated, I'm impressed with it and am learning to value it as another tool while I continue to use it more (though I'll always carry m/c). I noticed your (no, not PNP "you're" :wink: ) comment on battery types. My 60SCx owners manual mentions nothing of LI use. It specifically mentions Alkaline and NiMH use. The unit also has a specific setting within the setup menu for the use of either AK or NiMH batteries. Again, no mention of LI (lithium ion). Whether this means the unit is not compatible with LI batteries I do not know. Just thought I'd raise the point and perhaps the question of LI use with this particular unit.


My 60csx has a setting for "Li-ion". Garmin started getting complaints, so they probably took the setting off the menu. There is/was a technical note at the Garmin site, instructing users to first discharge the batteries a little before using them in the 60cs series. I put new Li metal in my older 60c for about 20-30 minutes, then transfer them to the 60csx to make sure the unit will stay on. So any pair of Li AA batteries in the pack as "back-up" for a 60csx should first be discharged and tested in the unit. If they still have too high a voltage, the 60csx will fade off shortly after you hit the power button (There is protective circuitry in the unit to prevent over voltages.)

Once the initial voltage spike is over, there is the ironic opposite problem; the discharge voltage varies so slowly, that the battery meter will indicate "full" for Li metal till the last moment, when the batteries really have just a half hour of life. But I've had a pair of Li metal last for over 30 hours in my 60csx. I use Li-metal when I'm going on a backpack trip that lasts a few days.

The "safest" thing for you might be to carry extra alkaline AAs. Garmin tends to be paranoid about over-promising, and some of the literature on the website is very conservative, if not just wrong. However, alkalines don't do very well in cold, whereas Li metal do very well.

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 3:41 am

What is the source of the disagreement between Rob and DMT?


I'm glad you asked. Global warming is causing an increase in edginess in many people, you !@#$%^& sh*thead.

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The Chief

 
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by The Chief » Wed Jan 14, 2009 3:46 am

MoapaPk wrote:
What is the source of the disagreement between Rob and DMT?


I'm glad you asked. Global warming is causing an increase in edginess in many people, you !@#$%^& sh*thead.


It aint GW... just plain GAS!

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 4:14 am

Looks to me like another case of stolen bandwidth.

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woodsxc

 
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by woodsxc » Wed Jan 14, 2009 5:36 am

Dingus Milktoast wrote:
woodsxc wrote:
Dingus Milktoast wrote:
rhyang wrote:
Dingus Milktoast wrote:after I repeatedly invited and was rebuffed by another climber about the same route


I'm kind of expecting an explanation. I told you repeatedly what was going on with me. If you felt 'rebuffed', then I am confused :?

If you had mentioned this to me privately, then I could have explained in more detail. But if you are going to slander me in public or tell stories behind my back .. what the hell ?

Oh screw it .. I have plenty of friends to climb with. If you are going to be like this, then have a nice life dude.


To quote aprevious poster:

"
OK, that was a cheap shot "

See when you used THAT example and then added you 'expected' that response?

Oh screw it. I have plenty of friends. If you are going to take cheap shots and then play the holier than thou card you can, have a nice life dude.

DMT


The maturity on both sides here is stunning.

If you want to fight this out to the bitter and unsatisfactory ending, do it elsewhere.


Image

DMT


Image

This will get you to approximately the same place.

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The Chief

 
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by The Chief » Wed Jan 14, 2009 5:42 am

Hey HW (MoapaPK), I spent the last twenty or so minutes looking through your website and photos's.

Dude, you definitely need a 12 Step Program for your addiction to that GPS'!

You'd be lost if you ever took that thing off from around your neck!

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MoapaPk

 
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by MoapaPk » Wed Jan 14, 2009 6:38 am

The Chief wrote:Hey HW (MoapaPK), I spent the last twenty or so minutes looking through your website and photos's.

Dude, you definitely need a 12 Step Program for your addiction to that GPS'!

You'd be lost if you ever took that thing off from around your neck!


The object around my neck is a camera case, not a GPS. Generally, a GPS should be situated where it won't be blocked by a microwave absorber.

I guess you have a lot of experience with 12 step programs, but I'm sure I'd be OK without the GPS. Tthe GPS does accompany me on most trips, even if I never consult it. Sometimes I use it just to do a post-mortem-- like to find my average speed during last Saturday's slide.

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