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Over-estimating your experience or under-estimating the terrain in a place like Big Bend can result in serious injury or death. Use the information and advice found here wisely. Climb/Hike/Camp/Drive at your own risk.

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DID YOU KNOW?

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SHANEA

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DID YOU KNOW?
« on: October 15, 2006, 02:00:38 PM »
http://home.nps.gov/bibe/parknews/upload/BIBE-facts-2006.pdf

2006 BIBE FACT SHEET...  Just the facts maam.

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Offline okiehiker

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FACT? sheet
« Reply #1 on: October 15, 2006, 10:47:57 PM »
How come it always says that the lowest point in BIBE is 1,850'?  At the east end of the park, downstream from Boquillas Canyon the elevation is as low as 1,700'.  Just because it is hard to get to doesn't mean it doesn't exist.  

And btw, is Emory 7,825'; 7,832' or 7,835??  :shock:
Funny... I have a story about that...

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chisos_muse

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Re: FACT? sheet
« Reply #2 on: October 16, 2006, 05:59:31 AM »
Quote from: "okiehiker"
How come it always says that the lowest point in BIBE is 1,850'?  At the east end of the park, downstream from Boquillas Canyon the elevation is as low as 1,700'.  Just because it is hard to get to doesn't mean it doesn't exist.  

And btw, is Emory 7,825'; 7,832' or 7,835??  :shock:


Perhaps you should email the BIBE Webmaster with these questions? :?

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BigBendHiker

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Re: DID YOU KNOW?
« Reply #3 on: October 16, 2006, 06:20:36 AM »
Quote from: "SHANEA"
2006 BIBE FACT SHEET...  Just the facts maam.


Thanks, Shanea!  Some good factoids there.

(BTW, Jack Webb is smiling with your closing)



BBH

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Offline The Scorpion

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Re: FACT? sheet
« Reply #4 on: October 16, 2006, 10:33:42 PM »
Quote from: "okiehiker"
How come it always says that the lowest point in BIBE is 1,850'?  At the east end of the park, downstream from Boquillas Canyon the elevation is as low as 1,700'.  Just because it is hard to get to doesn't mean it doesn't exist.  

And btw, is Emory 7,825'; 7,832' or 7,835??  :shock:


I think its 7825. here is a photo of my GPS unit from a hike up to the peak. however I did not officially complete the hike as I did not climb the last 25 ft to the top.





plus I guess it has a lot to do on where you hold the GPS unit to get your reading.

James
everything is better with bacon!!!

http://jamesb.smugmug.com/BigBendNationalPark/

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Offline presidio

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Re: FACT? sheet
« Reply #5 on: October 18, 2006, 09:08:40 PM »
Quote from: "jamesb"
I think its 7825. here is a photo of my GPS unit from a hike up to the peak. however I did not officially complete the hike as I did not climb the last 25 ft to the top.


plus I guess it has a lot to do on where you hold the GPS unit to get your reading.

James


You need to understand that GPS elevations will vary considerably from the surveyed figures. This is dependent upon a number of factors, including unit sensitivity, number of satellites visible to the unit, the spread of the satellites (broad spacing makes for better accuracy) and, most importantly, the fact that the elevation data displayed by a GPS is a mathematical calculation based on an ellipsoid. Thus, if you ever actually see your GPS match a given elevation, you simply were lucky to be looking at it then.

Here's why. The geoid approximates mean sea level. A significant difference exists between this mathematical model and the real object. However, even the most mathematically sophisticated geoid can only approximate the real shape of the earth.

The accuracy of GPS height measurements depends on several factors but the most crucial one is the "imperfection" of the earth's shape. Height can be measured in two ways. The GPS uses height above the reference ellipsoid that approximates the earth's surface. The traditional, orthometric height is the height above an imaginary surface called the geoid, which is determined by the earth's gravity and approximated by mean sea level. The difference between the two heights—the difference between the ellipsoid and geoid—is the geoid height.

This also relates to why you can never be absolutely accurate with horizontal distances without the use of differential correcting broadcasts from ground stations. When differentially corrected, horizontal accuracy can be in the sub-centimeter range and can be repeatedly demonstrated. With your handheld unit, returning several times to the point you plotted will bring you to a slightly different location each time.

None of this really matters much for non-legal uses. The GPS will more accurately show your location than you could determine from map and compass calculations (but which you still should know how to do).

It's been my experience that getting within 15 feet of what I am looking for has always been sufficient to find my car in the desert. :D  :D
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Wendell (Garret Dillahunt): It's a mess, ain't it, sheriff?
Ed Tom Bell (Tommy Lee Jones): If it ain't, it'll do till the mess gets here.
--No Country for Old Men (2007)

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Online Al

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DID YOU KNOW?
« Reply #6 on: October 18, 2006, 09:33:17 PM »
So you're saying that a GPS does not have a topography data base built into it correlated to location but provides an estimated elevation based on a mathmatical model (approximation) of Earth's surface?

Al


To the extent I understand what you said, Great job!

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Offline Desert Rat

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DID YOU KNOW?
« Reply #7 on: October 18, 2006, 09:39:05 PM »
Most GPS units will display an "estimated precision figure", or accuracy estimate, which apllies to horizontal accuracy and is frequently optimistic.  A good rule of thumb is to figure vertical error is 1 ? times greater than the horizontal error.

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Offline presidio

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DID YOU KNOW?
« Reply #8 on: October 18, 2006, 11:17:47 PM »
Quote from: "Al"
So you're saying that a GPS does not have a topography data base built into it correlated to location but provides an estimated elevation based on a mathmatical model (approximation) of Earth's surface?


That is correct.

Quote
To the extent I understand what you said, Great job!


Well, thank you.

There is some major science and math behind that marvelous little device you hold in your hand. One of the best bargains ever....for around $150-$500 for a receiver you get to use the rest of a $14 billion system for free. Money well spent in my book, considering what it does and how useful it is. I remember when the constellation was not complete and you would have hours at a time when no useable signal was receivable; we would wait expectantly, hoping for a third satellite so we could get 2D positions, or a fourth satellite for 3D. It wasn't all that long ago...around 1996 or so.

One other thing that is pretty amazing about GPS units is that they are not receiving any position data from the satellites at all. They actually are calculating your position based on the timing signals (and thus their position in space) from the satellites.

The GPS units use an ephemeris table received from the satellites to predict/project their future locations. This is why your GPS can find the correct satellites and compute your location relatively quickly when it has been off for a while, and also why the longer it is off or the farther you move from its last position while off will cause it to take longer and longer to acquire the correct signals and location.
_____________
<  presidio  >
_____________
Wendell (Garret Dillahunt): It's a mess, ain't it, sheriff?
Ed Tom Bell (Tommy Lee Jones): If it ain't, it'll do till the mess gets here.
--No Country for Old Men (2007)

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Offline BIBE Webmaster

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It's official
« Reply #9 on: October 21, 2006, 07:49:26 PM »
Satellite mapping several years ago set the offical measurement of Emory Peak at 7,832'.

E
Eric Leonard, Park Ranger
Big Bend National Park / Rio Grande Wild & Scenic River
http://www.nps.gov/bibe/
http://www.nps.gov/rigr/

(Big Bend Park Ranger 2004-2008)

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Offline Desert Rat

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DID YOU KNOW?
« Reply #10 on: October 21, 2006, 08:06:59 PM »
Thanks, Eric.

 


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