# Most accurate coordinates?

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5{ of a brain fart, I know which set of coordinates Geocaching uses. But out of the following list which one is the most accurate?

1) deg/min.mm

2) deg/min.mmm

3) deg/min/sec

4) deg.ddddd

If I remember correctly the last one on the list is the most accurate

[This message was edited by magellan315 on November 15, 2002 at 06:30 PM.]

Is easier to work with but! the more decimal points that you have? the more accurate.......>>> D/M/S is what the original maps were layed out with, hence the grid or rectangular form of measurement. Whichis based on time and Greenwich being the 0 Degree hour, 15 45 60 75 90 105 120 ect. to 180 Standard Lines

When all else fails Geotry again.

Little confused by the last post, to many hours at work, not enough sleep. Please keep it simple, the most accurate type of coordinates to use is:

1.2.3. or 4.

Thanks

Trailblazer #1

Technically speaking, latitude/longitude is neither a grid or a rectangular system. It is an angular coordinate system and the lines of latitude and longitude are called graticules.

Magellan315

You are confusing accuracy with resolution. The coordinates with the greatest resolution is #4 deg.ddddd which gives a resolution of 3.6 feet.

Poindexter,

www.geocities.com/fairbank56

It's all kinda moot anyway. The level of precision on the GPS receivers are all more than the accuracy of the units. In other words, the last decimal points on H DD MM.MMM are between 4-6 feet in most areas, but the accuracy is only 16-17 feet on the better models.

So it really doesn't matter.

Markwell

Chicago Geocaching

How much wood would a wood chuck chuck if a wood chuck could chuck wood?

Team Shuey

Riverview, Florida

Shuey's Web Site

quote:
Originally posted by Team Shuey:

How much wood would a wood chuck chuck if a wood chuck could chuck wood?

I thought it went along these lines. A Skunk sat on a Stump - The Stump thought the Skunk Stunk - So who Stunk - The Skunk or the Stump

Tahosa - Dweller of the Mountain Tops.

You have to be carefull to remember that Degrees are a unit of angular measurement, and only translate into psyical distances when maped to the globe. "Accurate" would not be the right term to use. You are asking about Precision or Resolution. Lets see if this helps for some:

Assume that "Resolution" indicated how many different psyical points can be created and displayed within ONE UNIT.

In this case, we will use ONE DEGREE as the Unit.

Therefor, in one degree you can specify ONE point.

Next, shifting to Minutes, which are by definition 1/60 of a Deg, you could specify 60 points witin a degree. But using 2 decimal places for a minute you can have 60 x 100 = 6000 points then. So MM.MM gives 6000 points within a degree. Using 3 decimal places is 60 x 1000 for 60,000 points within a degree.

Next is Deg/Min/Sec. Which by definition a second is 1/60 of a Minute. So there are 60 seconds in a min, and 60 min in a deg. So thats 60 x 60 = 3600 individual points you can have within a Degree.

Lastly, there is Deg.ddddd A degree to 5 decimal places. Thats 100,000 points within one degree. By far the biggest number of points you can specify within the unit, so it has more Resolution then any of the other formats.

So a recap, from least resolution to most -

DEGREE 1

D MM SS 3600

D MM.MM 6000

D MM.MMM 60000

D.DDDDD 100000

Got it?

quote:
Originally posted by Team Shuey:

How much wood would a wood chuck chuck if a wood chuck could chuck wood?

A woodchuck would chuck as much wood as a woodchuck could chuck if a woodchuck could chuck wood. Of Course.

"We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile. We are the Borg."

If a GPS unit displayed coordinates but no one was around to see it , would it make a waypoint sound? Think about THAT one for awhile...

quote:
Originally posted by the Arpy Team:

If a GPS unit displayed coordinates but no one was around to see it , would it make a waypoint sound? Think about THAT one for awhile...

If it was an eTrex line, then no, since they don't make sounds.

"We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile. We are the Borg."

Use native mode.

Anytime you specify a different system the internal algorithm introduces a small error in conversion. Granted most of the time the error is out in decimal point land but occassionally a larger error shows up.

You will have much greater error from a high PDOP. It's just not the number of satellites, but their geometry. Anytime PDOP > 2 use the position reading with caution.

2 things with native coordinates and PDOP.

PDOP isn't displayed by too many receivers (at all) to know if it's greater then 2 or not. Besides PDOP can go a little higher than 2 without too many worries. The specifications are based on a PDOP of 6 or less.

Native coordinates aren't displayed by any recreational receivers either.

Cheers, Kerry.

I never get lost everybody keeps telling me where to go

I use Trimble equipment for most of my work-related stuff. For just playing I use a Garmin 3+. Mine always showed PDOP and native mode after a software patch.

You can use the unit with any PDOP you want. What error is acceptable or unacceptable is a personal matter.

Was the PDOP part of the software patch as well or part of the base 3+ display.

Be interested in obtaining that software patch if you could point in the right direction.

By native format one would assume you are referring to ECEF XYZ, which is the underlying (and native) GPS coordinate system.

Cheers, Kerry.

I never get lost everybody keeps telling me where to go

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