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Most accurate Lat/Long format for a eTrex. Whichy one'a deez works best?

#1 User is offline   SilentMunkey 

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Posted 13 September 2007 - 04:04 AM

I use the Garmin eTrex...the ugly lil cheap yellow one...

I was wondering which format is best for caching. Yesterday i found myself int he situation where I had written down the wrong format and had to change it in my GPS. I got to thinking...one of these has to be considered the most accurate.

For example:

Decimal 38.33915 -77.07127
DDD MM.MMM N 38 20.349 W 077 04.276
DDD MM SS.SSS N 38 20' 20.9400" W 77 4' 16.5612"


Which one is the best? The longest? =)

Just a question from a new cacher.

#2 User is offline   Timpat 

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Posted 13 September 2007 - 05:03 AM

View PostSilentMunkey, on Sep 13 2007, 08:04 AM, said:

I use the Garmin eTrex...the ugly lil cheap yellow one...

I was wondering which format is best for caching. Yesterday i found myself int he situation where I had written down the wrong format and had to change it in my GPS. I got to thinking...one of these has to be considered the most accurate.

For example:

Decimal 38.33915 -77.07127
DDD MM.MMM N 38 20.349 W 077 04.276
DDD MM SS.SSS N 38 20' 20.9400" W 77 4' 16.5612"


Which one is the best? The longest? =)

Just a question from a new cacher.

Ok, here goes. [Firstly, the DDD MM SS.SSS you use is only displayed to one tenth of a second (DDD MM SS.s) in my Garmin. For these examples we will use Latitude since this does not vary over the globe, where Longitude converges at each pole].

In this example: 38.33915 -77.07127, the 1/10 thousandth of a degree (5th decimal place) equals ~36.46 feet.
In this example: 38 20.349, the one thousandth (3rd decimal place) of a minute equals ~6 feet.
In this example: 38 20' 20.9", the tenth of a second equals ~10 feet.

So your answer is to use the conventional GPS format of DDD MM.mmm to refine your position to within the capability of the unit. And I have to mention, any one of these formats are within the expected accuracy of our handheld units anyway, so it's really an academic question.

This post has been edited by Timpat: 13 September 2007 - 05:05 AM


#3 User is offline   dogwalkers2 

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Posted 13 September 2007 - 06:07 AM

Quote

In this example: 38.33915 -77.07127, the 1/10 thousandth of a degree (5th decimal place) equals ~36.46 feet.

Actually, one degree is about 60 X 6076 = 364560 feet, therefore the fifth decimal point makes it about 3.6456 feet, making it the most precise.

But, as you said, academic...The precision of each format is less than the accuracy of the system.

#4 User is offline   gallet 

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Posted 13 September 2007 - 06:20 AM

I like decimal degrees as the decimal places roughly equal metres. So the second decimal place roughly equals kilometres. Also one is less likely to make errors when inputting manually.

This post has been edited by gallet: 13 September 2007 - 06:21 AM


#5 User is offline   Timpat 

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Posted 13 September 2007 - 07:47 AM

View Postdogwalkers2, on Sep 13 2007, 10:07 AM, said:

Actually, one degree is about 60 X 6076 = 364560 feet, therefore the fifth decimal point makes it about 3.6456 feet, making it the most precise.

I stand corrected. Thanks dogwalkers2 for pointing out my error in math! Guess I'm like the character Michael Bolton in "Office Space" where he misplaces a decimal point when writing his money-stealing software program. :)

#6 User is offline   LinXG 

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Posted 13 September 2007 - 11:09 AM

one of these has to be considered the most accurate.?

This is a a very odd statement. All three of the co-ordinates you listed point to exactly the same location. Accuarcy is not an issue at all here! The format simply presents the same information in three different ways.

Which one is the best? The longest? =)

Geocaching.com posts all locations using degree, decimal minute or UTM.

Use either one and you should do fine.

#7 User is offline   BelchFire 

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Posted 13 September 2007 - 12:06 PM

View PostLinXG, on Sep 13 2007, 03:09 PM, said:

one of these has to be considered the most accurate.?

This is a a very odd statement. All three of the co-ordinates you listed point to exactly the same location. Accuarcy is not an issue at all here! The format simply presents the same information in three different ways.

Which one is the best? The longest? =)

Geocaching.com posts all locations using degree, decimal minute or UTM.

Use either one and you should do fine.

LinXG,

I agree that the question could have been phrased differently, however, I understood exactly what he wanted to know. Perhaps he could have asked "Which format offers the highest resolution?"

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