Why the funny coordinate format?

[tiiiim]

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates? It doesn't seem to make any sense: either use full decimal degrees, or the entire degrees-minutes-seconds....

 

(My only guess is that it has something to do with legacy GPS units - I use a netbook to geocache, so wouldn't really know....)

[+webscouter.]

It is the coordinate system that most GPS units are set to when they are sold.

[knowschad]

Dang. I came here hoping to hear a joke.

 

"Hey... did you hear the one about the coordinate format?"

[+zoltig]

 

"Hey... did you hear the one about the coordinate format?"

No. Do tell.

[+Chrysalides]

 

"Hey... did you hear the one about the coordinate format?"

No. Do tell.

Oh, you know. Just because you have a degree doesn't mean you know how to use it.

 

(sorry. but you did ask )

[GOF and Bacall]

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates? It doesn't seem to make any sense: either use full decimal degrees, or the entire degrees-minutes-seconds....

 

(My only guess is that it has something to do with legacy GPS units - I use a netbook to geocache, so wouldn't really know....)

 

A netbook to geocache? Sounds like an expensive accident looking for a creek to happen in.

[knowschad]

"Hey... did you hear the one about the coordinate format?"

No. Do tell.

Oh, you know. Just because you have a degree doesn't mean you know how to use it.

(sorry. but you did ask )

Ba-da-BOOM!!

[+fishgeek]

The DD MM.mmm format gives you 1/1000th of a minute - much more precise than the DD MM SS format, which is only 1/60th of a minute. The DD.ddddd is not commonly used.

 

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates? It doesn't seem to make any sense: either use full decimal degrees, or the entire degrees-minutes-seconds....

 

(My only guess is that it has something to do with legacy GPS units - I use a netbook to geocache, so wouldn't really know....)

Edited February 8, 2010 by fishgeek

[+StarBrand]

Nothing funny about it to us.

 

Just new to you is all.

[+thedeadpirate]

We take our coordinate formats seriously around here buster.

[+simpjkee]

I got my 1st GPS after my first couple finds. A couple months later I saw a different coord format on a website and thought: "Oh wow, this website has their coordinates all fouled up".

[+Cardinal Red]

The DD MM.mmm format gives you 1/1000th of a minute - much more precise than the DD MM SS format, which is only 1/60th of a minute. The DD.ddddd is not commonly used.

Garmin units actually use DD MM SS.s which is 1/600th of a minute. Isn't that fairly typical of most units?

 

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

[knowschad]

I got my 1st GPS after my first couple finds. A couple months later I saw a different coord format on a website and thought: "Oh wow, this website has their coordinates all fouled up".

"Fouled" up? LOL! Now, THAT is funny!!

[+Chrysalides]

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

Why? After all, they say every minute counts.

 

*ahem* Sorry.

 

Seriously, out of curiosity, why do you like decimal degrees? I find having a string of 5 numbers together a little harder to see.

[jholly]

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

Why? After all, they say every minute counts.

 

*ahem* Sorry.

 

Seriously, out of curiosity, why do you like decimal degrees? I find having a string of 5 numbers together a little harder to see.

 

Yes, but with decimal degrees you won't be a minute or two to short.

[knowschad]

Yes, but with decimal degrees you won't be a minute or two to too short.

Sorry, but I NEVER get to do that.

[jholly]

Yes, but with decimal degrees you won't be a minute or two to too short.

Sorry, but I NEVER get to do that.

 

Well went fishing for flask and get knowschad. Not what I wanted, throwing it back.

[+DENelson83]

I guess I use HDDDMMSS.S because I just want a "second" chance...

Edited February 8, 2010 by DENelson83

[+bittsen]

I don't think I could handle decimal degrees. I still haven't gotten used to Celcius!

[tiiiim]

A netbook to geocache? Sounds like an expensive accident looking for a creek to happen in.

 

I don't hold it out in front of me when geocaching - well, not anymore anyway!! It's in my rucksack, and I've written a script which speaks the bearing and distance to the destination coordinate through my headphones. That way, the only thing visible is a compass and if I were to drop that in a creek, that's £5 to fix!!

 

The DD MM.mmm format gives you 1/1000th of a minute - much more precise than the DD MM SS format, which is only 1/60th of a minute. The DD.ddddd is not commonly used.

 

The DD.dddd format IS commonly used - how does anything digital compute bearing, distance etc etc? Certainly not in minutes and seconds - it'll convert to DD.dddd first, calculate, then convert back if required for the user. All the apps on my netbook require coordinates in DD.dddd.

 

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

 

Me too, hence the question! It's a pain in the backside trying to convert from DD MM.mmmm to DD.dddd whilst out hunting for a multi! But it seems that the answer to my question is because that's what GPS units are set to by default.

[+Indotguy]

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates? It doesn't seem to make any sense: either use full decimal degrees, or the entire degrees-minutes-seconds....

 

(My only guess is that it has something to do with legacy GPS units - I use a netbook to geocache, so wouldn't really know....)

 

A netbook to geocache? Sounds like an expensive accident looking for a creek to happen in.

 

I doubt this device has ever seen a creek. It's probably more likely to be dropped on a sidewalk or Wally world parking lot. By the way, what's so funny about about the decimal minute format?

[tiiiim]

I doubt this device has ever seen a creek. It's probably more likely to be dropped on a sidewalk or Wally world parking lot. By the way, what's so funny about about the decimal minute format?

 

I'll let that dig pass by (check my found caches to see you couldn't be more wrong).

 

As far as what's 'funny' about the decimal minute format: it just seemed weird that with two different types of coordinate formats available (main types, anyway: decimal degrees and degrees-minutes-seconds), the site is using one which is a mixture of both. Hell, even GPX files use the decimal degrees format. Now I know it's due to (most) GPS units using the format by default on the user side. From a personal point of view, it was a PITA to have to convert from DD MM.mmmm when trying to complete multis with my netbook.

[+NYPaddleCacher]

The DD MM.mmm format gives you 1/1000th of a minute - much more precise than the DD MM SS format, which is only 1/60th of a minute. The DD.ddddd is not commonly used.

 

 

Actually DD.ddddd *is* commonly used. It's used everytime you download a waypoint. Both GPS and LOC formats represent LAT/LONG values in DD.ddddd format. It's only converted to DD MM.mmm for display on the website and on a GPS.

[+larryc43230]

From a personal point of view, it was a PITA to have to convert from DD MM.mmmm when trying to complete multis with my netbook.

You might want to take a look at FizzyCalc. It might help to make those conversions go more smoothly.

 

--Larry

[tiiiim]

From a personal point of view, it was a PITA to have to convert from DD MM.mmmm when trying to complete multis with my netbook.

You might want to take a look at FizzyCalc. It might help to make those conversions go more smoothly.

 

--Larry

 

Thanks for that - looks interesting. I eventually wrote some code of my own to do the conversions within my scripts, but it's not pretty!! Also, the netbook runs Linux so FizzyCalc wouldn't really work (don't start on Wine...), but it looks like a simple option for those that do run Windows.

[+Isonzo Karst]

I wondered that myself when I started. Decimal Degrees is what I'd call standard.

 

MUCH easier to enter DegDec into coordinate boxes. Indeed, when I write Wherigo carts, the first thing I do is set the coordinate standard to Degrees Decimal so I can easily copy and paste from my own .gpx files, also in DegDec.

 

There's a conversion page on GC.com it's linked on every cache listing (other conversions)

 

http://www.geocaching.com/wpt/

 

For this site, I'm using Prime's excellent waypoint entry script so I don't have to type coords into boxes. Lordy.

[GermanSailor]

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates?

Because this is the most common format in navigation. Degrees, Minutes and Seconds are rarely used and just confusing.

 

One minute equals one nautical mile, this make working with marine charts easy.

 

GermanSailor

[tiiiim]

One minute equals one nautical mile...

 

Is this actual fact, or rule of thumb? Seems a bit hard to believe, since the Earth is a sphere (and a not very good one at that) so longitude lines are closer nearer the poles...

[+tozainamboku]

The DD.dddd format IS commonly used - how does anything digital compute bearing, distance etc etc? Certainly not in minutes and seconds - it'll convert to DD.dddd first, calculate, then convert back if required for the user. All the apps on my netbook require coordinates in DD.dddd.

 

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

 

Me too, hence the question! It's a pain in the backside trying to convert from DD MM.mmmm to DD.dddd whilst out hunting for a multi! But it seems that the answer to my question is because that's what GPS units are set to by default.

What's funny is that computer isn't using decimal degrees to compute bearing, distance, etc. Down in the code somewhere the latitude and longitude are converted to radians for use in the trigonometric functions used in the computation. It is likely that some GPS units are internally storing the values in radians already. And beyond this the GPS is actually computing location in geocentric Cartesian coordinates and then converting to latitude and longitude (or other grid system) using one of many selectable datums. Most GPS units have options to display the coordinates in many different formats. Some people insist on displaying coordinates in UTM or in the British National Grid format in order to work with paper maps. (This may require a change in the datum as well as the format) Decimal minutes and DMS are available because that is what many people are used to. It only seems funny to someone who is programming because decimal degress is a simple scalar. You are used to programming using real numbers. Having to to write an integer plus a real number or two integers and a real number seems cumbersome. But it's relatively simple to do. Internally keep the value as degrees (or radians) and simply write I/O routine to handle the different cases.

 

Geocaching.com uses DD MM.MMM because that is format that most GPS units came set to out of the box. As more people geocache using cell phones and netbooks there may be a reason to change to accomodate them. As has been pointed out the GPX and LOC file formats use decimal degrees.

[+Chrysalides]

One minute equals one nautical mile...

Is this actual fact, or rule of thumb? Seems a bit hard to believe, since the Earth is a sphere (and a not very good one at that) so longitude lines are closer nearer the poles...

Fact. http://en.wikipedia.org/wiki/Nautical_mile#History

 

But it's "approximate" because the Earth is not a perfect sphere. But it's close enough.

[tiiiim]

One minute equals one nautical mile...

Is this actual fact, or rule of thumb? Seems a bit hard to believe, since the Earth is a sphere (and a not very good one at that) so longitude lines are closer nearer the poles...

Fact. http://en.wikipedia.org/wiki/Nautical_mile#History

 

But it's "approximate" because the Earth is not a perfect sphere. But it's close enough.

 

Ah, that's cool, though only applies to latitude. Every day's a school day!

[+addisonbr]

Ah, that's cool, though only applies to latitude. Every day's a school day!

Agreed. Thanks for the link Chrysalides.

[+Cardinal Red]

Even though I understand the reason we don't, I really wish we used the DD.ddddd format instead.

Seriously, out of curiosity, why do you like decimal degrees? I find having a string of 5 numbers together a little harder to see.

My reason is the same as that expressed above by Isonzo Karst.

MUCH easier to enter (mostly copy/paste in my case) Decimal degrees into coordinate boxes.

Only one coordinate box for Lat and one coordinate box for Long. I hate the multiple copy/pastes usually required.

Edited February 8, 2010 by Cardinal Red

[+Chrysalides]

Only one coordinate box for Lat and one coordinate box for Long. I hate the multiple copy/pastes usually required.

I hate multiple copy / pastes as well. Tedious, repetitive stuff should be done by a computer. Some programmers apparently don't remember that. One single textbox that will try to figure out what you typed in is not exactly complicated - one example is the corrected coordinates entry in GSAK.

[+Flag_Mtn_Hkrs]

Only one coordinate box for Lat and one coordinate box for Long. I hate the multiple copy/pastes usually required.

I hate multiple copy / pastes as well. Tedious, repetitive stuff should be done by a computer. Some programmers apparently don't remember that. One single textbox that will try to figure out what you typed in is not exactly complicated - one example is the corrected coordinates entry in GSAK.

 

I agree. I think it is easier in my mind to work with DDD.DDDDD than anything else. I premium member should be able to change their default if they wish. Once changed all information for that user would be displayed in what ever format they choose.

 

I wish Groundspeak would get on the ball with this one.

[+Harry Dolphin]

The DD MM.mmm format gives you 1/1000th of a minute - much more precise than the DD MM SS format, which is only 1/60th of a minute. The DD.ddddd is not commonly used.

 

Should hopefully be a simple one to answer: why oh why does Groundspeak use the degrees and decimal minutes format for coordinates? It doesn't seem to make any sense: either use full decimal degrees, or the entire degrees-minutes-seconds....

 

(My only guess is that it has something to do with legacy GPS units - I use a netbook to geocache, so wouldn't really know....)

 

But, precision without accuracy is meaningless.

[+NicknPapa]

One minute equals one nautical mile...

 

Is this actual fact, or rule of thumb? Seems a bit hard to believe, since the Earth is a sphere (and a not very good one at that) so longitude lines are closer nearer the poles...

 

One degree of longitude AT THE EQUATOR or one degree of latitude equal 1.15 miles or just under one nautical mile (1.16 miles)

[+tozainamboku]

One minute equals one nautical mile...

 

Is this actual fact, or rule of thumb? Seems a bit hard to believe, since the Earth is a sphere (and a not very good one at that) so longitude lines are closer nearer the poles...

 

One degree minute of longitude AT THE EQUATOR or one degree minute of latitude equal 1.15 miles or just under one nautical mile (1.16 miles)

The original definition of a nautical mile was one minute of latitude. Longitude was much harder to measure and besides it varies based on your latitude. Later a nautical mile was standardized at 1,852 meters. Since the reference model for latitude and longitude have changed with accurate measurement the Earth's ellipsoid (we now use the WGS-84 datum) the length of one minute of latitude varies from approximately 1842.9 m at the Equator to approximately 1861.7 m at the poles, with a mean value of 1852.3 m which is very close to one nautical mile. The length of one minute of longitude at the equator is approximately 1855.325 m or just slightly over one nautical mile.

Edited January 28, 2011 by tozainamboku

[benji55545]

I like the DD MM.mmm format, but that's probably just because I'm used to it. I DO get really annoyed when I try to plot geocache waypoints in ArcGIS though. The program really doesn't like that format, so I had to convert everything to DD.ddddd. I ended up doing all the conversions in Excel and everything worked out alright.

 

But seriously, shouldn't ArcGIS be able to work with any coordinate format easily? Seems like a pretty stupid limitation.

[+Markwell]

N 41 48.296 W 88 07.636 to N 41 48.297 W 88 07.636 is 6.083 ft

N 41 48 17.78 W 88 07 38.15 to N 41 48 17.79 W 88 07 38.15 is 1.032 ft

N 41.80494 W 88.12726 to N 41.80495 W 88.12726 is 3.643 ft

16T E 406358 N 4628733 to 16T E 406358 N 4628734 is 3.279 ft

 

Garmin says "Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters on average." - that seems pretty wide - like 45 feet. I like this Brighthub answer better, as it seems to be the same number that we've been saying for years on these forums: "Today's GPS navigation receivers are much more accurate than early models, and with systems like Differential GPS, can typically offer precision within 10 meters." (although they mean "accuracy")

 

Conclusion:

Any of the displayed formats of the GPS's position are close to 5 to 10 times more precise than the ACCURACY of the unit.

 

Here's your comparative thought process:

Let's say you want to know when to celebrate my son's birthday. Right now, in my local time zone Jan 29 2011 3:20:40 PM. I'll tell you the number of days since he was born. If I told you he was born X number of days ago, and you wanted to know his birthday I could tell you in days, but I'd need to add decimals to the number of days to give you more precision:

 

0 decimal points, it would be 5597 days, which would give you Oct 3 1995 15:20:40

1 decimal points, it would be 5596.6 days, which would give you Oct 4 1995 00:56:40

2 decimal points, it would be 5596.64 days, which would give you Oct 3 1995 23:59:04

3 decimal points, it would be 5596.639 days, which would give you Oct 4 1995 00:00:30

4 decimal points, it would be 5596.6387 days, which would give you Oct 4 1995 00:00:56

5 decimal points, it would be 5596.63866 days, which would give you Oct 4 1995 00:01:00

6 decimal points, it would be 5596.638657 days, which would give you Oct 4 1995 00:01:00

7 decimal points, it would be 5596.6386574 days, which would give you Oct 4 1995 00:01:00

8 decimal points, it would be 5596.63865741 days, which would give you Oct 4 1995 00:01:00

 

Just telling you 5597 days isn't enough precision for the accuracy you need to calculate the correct answer. But if I use 7 or 8 decimal points, the difference between the last two numbers in the string (5596.63865741 and 5596.63865742) is less than one second difference - more precision that is necessary for an accurate answer.

 

Today's current GPS units display characters out to the point that the difference between two digits are less than 6 feet of difference, even for the worst display. But that difference is more precision than the accuracy of the unit itself. The unit is likely only accurate to about 30 feet. So it doesn't matter WHAT units the device uses, it's still not going to give you any better readings and accuracy if you switch to DD MM SS.S or DD.DDDDD or UTM. No matter what, the coordinates are still going to be fuzzy.

 

So Geocaching.com and Groundspeak looked at the units and say that FOR THE MAJORITY, units out of the box use DD MM.MMM as the default coordinate system. Since Geocaching.com is supposed to be an activity that takes very little prep to be able to do (that's its appeal) it's better to make it so that when people power up their GPS, they don't have to go read the manual or come into the forums to ask "why don't my coordinates match" or "how do I change the coordinates to match Geocaching.com" questions.

Edited January 29, 2011 by Markwell

[+dfx]

The OP should ask the question to whoever came up with the NMEA 0183 format, because the DDD MM.mmmm format is used exactly there.

[+Markwell]

Found a better article on Brighthub, while it doesn't give a definitive answer, it mentions the "95 Percent Confidence accuracy of 10 meters"

[+n0k1a]

I've wondered about this myself for a long time. I understand the GC site using DD MM.MMM due to that being the default units displayed by many GPS receivers. However, I do not understand why that choice was made by the GPS manufacturers. Hard copy maps, surveyors, and so on use DD MM SS[.SSS] extensively. Computer mapping systems use DD.DDDDD extensively (look at the HTML source for any cache page, and look at the format for the coords in most of the online map URLs for a particularly ironic example).

 

DD MM.MMM also seems to me to be a bizarre hybrid. It's reminiscent of the US 'standard' for dates, which also makes no sense: month-day-year. Either make it day-month-year, or year-month-day; why jump erratically between different-sized units? Actually, that may be even worse...it would be like MM SS DD!

 

DD.DDDDD would indeed facilitate copy and paste of coords in a much more friendly manner, as it would require only one field each for latitude and longitude. Making selection of DD.DDDDD available to premium members would be quite beneficial IMO.

[+webscouter.]

I've wondered about this myself for a long time. I understand the GC site using DD MM.MMM due to that being the default units displayed by many GPS receivers. However, I do not understand why that choice was made by the GPS manufacturers.

 

I would guess that the GPS manufacturers used DD MM.MMM because that is what pilots and sailors use on their maps.

Edited January 30, 2011 by webscouter.