Lat & long... degrees, minutes, seconds

[rsn48]

Occasionally I get brain farts over the most simple of things. And I may have looked up how to correct whatever, or do whatever, but invariably ten minutes later, it does a disappearing act in my brain.

Take the word "guarantee," I have looked up the proper spelling, without exaggeration at least one hundred times, and even typing this sentence I had to do a spell correct on it. Same with "it's" and "its," although after decades of trying to sort the correct usage out of these two simple words, I've finally got it, its something I've worked on for a long time.

And now in a system, a simpleton like me could understand, I got degrees, minutes and seconds. But then some genius decided that this system was to easy to remember and now "seconds" in to three decimal places? So am I suppose to take 60 seconds and divide it my 100, and that's how it works. And why was it changed, I think part one of the answer has to do with GPS, but why?

 

[Benthic2]

You'll want to divide the seconds by 60. For example 30 seconds, which intuitively you know should be half a minute 30/60 = .5

 

[RCook]

RSN,

Are you sure you aren't looking at degrees and minutes, with minutes to three decimal places?

On my charting system (Coastal Explorer) I get to choose whether lat/lon is displayed that way, or as degrees minutes and seconds, with seconds to two decimals.

That's how I remember my previous chartplotter as well.

 

[caltexflanc]

One second of latitude is about 100 feet everywhere , and of longitude about 80 feet here in the USA . So now that GPS has become so precise, it was decided to offer decimals as an alternative.

 

[twistedtree]

RSN,

Are you sure you aren't looking at degrees and minutes, with minutes to three decimal places?

On my charting system (Coastal Explorer) I get to choose whether lat/lon is displayed that way, or as degrees minutes and seconds, with seconds to two decimals.

That's how I remember my previous chartplotter as well.

That's correct, but it also works out that the decimal part is the same as the seconds/60 So 4.5 minutes is the same as 4 minutes, 30 seconds. And 30/60 is .5

 

[twistedtree]

One second of latitude is about 100 feet everywhere , and of longitude about 80 feet here in the USA . So now that GPS has become so precise, it was decided to offer decimals as an alternative.

This would be quite different, so very important to distinguish between seconds with a decimal, and minutes with a decimal. I haven't paid a tom of attention to it, but I think degrees and decimal minutes is the more common format for marine applications.


Does anyone's chart plotter or GPS display degrees, minutes, and seconds (or decimal seconds)?

 

[rslifkin]

Does anyone's chart plotter or GPS display degrees, minutes, and seconds (or decimal seconds)?

I'd have to look to confirm what my plotter displays. My Standard Horizon VHFs are degrees and decimal minutes. I know OpenCPN has a setting to choose between degrees and decimal minutes vs degrees, minutes, seconds.

 

[AusCan]

This would be quite different, so very important to distinguish between seconds with a decimal, and minutes with a decimal. I haven't paid a tom of attention to it, but I think degrees and decimal minutes is the more common format for marine applications.


Does anyone's chart plotter or GPS display degrees, minutes, and seconds (or decimal seconds)?

My Garmin has a choice between degrees, minutes & seconds or decimal degrees. Decimal degrees makes more sense to me. Perhaps not for those who haven't yet converted to metric.

 

[Codger2]

Does anyone's chart plotter or GPS display degrees, minutes, and seconds (or decimal seconds)?

Mine does. You have to enlarge to see the Lat/lon data.

 

[twistedtree]

Mine does. You have to enlarge to see the Lat/lon data.

That looks like decimal minutes. Is that what you meant?

 

[caltexflanc]

I think we are having some semantic confusion here. Decimal minutes = decimal (of minutes) instead of seconds.

 

[caltexflanc]

In reading yesterday's LNMs, I was reminded that the CG uses decimal seconds, as in 40° 4' 37.0236" N, 66° 27' 28.6626" W

Now there's some precision for you. So when calling in a position, know exactly what you are telling them .

 

[Codger2]

That looks like decimal minutes. Is that what you meant?

Yes

 

[oguidry]

The USCG still uses DMS in the Light List as in 32-45-28.526N.

As mentioned, one minute equals 6,068 feet and one-second equals 101 feet. So a tenth (0.1) of a second is 10 feet, a hundredth (0.01) of a second is 1 foot and a thousandth (0.001) of a second is 0.1 foot.

Decimal seconds are superfluous.

 

[High Wire]

That is a good question "What is the standard that we should be using here in the
US as cruisers?"
I have always used DDMM.MMM with electronics.

 

[caltexflanc]

Whatever you choose, when reporting a position, be very clear what the numbers represent. And try to make sure that all your GPS devices (Epirb, AIS, VHF etc use the same format. Some folks still navigate with paper charts or really old electronics, so can still only report approximate DMS.

 

[twistedtree]

The USCG still uses DMS in the Light List as in 32-45-28.526N.

As mentioned, one minute equals 6,068 feet and one-second equals 101 feet. So a tenth (0.1) of a second is 10 feet, a hundredth (0.01) of a second is 1 foot and a thousandth (0.001) of a second is 0.1 foot.

Decimal seconds are superfluous.

Not sure what you mean by the last statement. You example is decimal seconds, i.e. you show seconds with 10ths, 100th, and 1000ths.

 

[twistedtree]

Whatever you choose, when reporting a position, be very clear what the numbers represent. And try to make sure that all your GPS devices (Epirb, AIS, VHF etc use the same format. Some folks still navigate with paper charts or really old electronics, so can still only report approximate DMS.

I agree that this is the important thing. It's REALLY important to know the difference between the two, and to be clear which you are talking about.

 

[SteveK]

This is my preferred
Degrees, Minutes and Seconds
DDD° MM' SS.S"
32° 18' 23.1" N 122° 36' 52.5" W

A good explanation is found here

 

[Shrew]

I use Decimal Minutes.

.25 = 15 seconds
.50 = 30 seconds
.75 = 45 seconds

I guess I'm spatially oriented. In my mind I superimpose a pie chart on an analogue clock face. I don't divide in my head. You can easily round up the last two digits which end up being statistically insignificant because at that point your in single digit feet.

.2557 becomes .26 = roughly 15 seconds

 

[bayview]

seems like multiple digits resolution in the seconds exceeds the GPS accuracy

 

[psneeld]

An often made mistake is reporting cursor position rather than ship position when excited.

Check that too and go slow and accurate when reporting position. It's way more important than most info passed back and forth in rescue ops.

 

[caltexflanc]

seems like multiple digits resolution in the seconds exceeds the GPS accuracy

Depends on the equipment and purpose. They measure tectonic plate movement in millimeters.

 

[rsn48]

I'm kind of a simpleton and I like things that are easy to grasp, especially in a crises.

Back in the day I took many graduate courses from a PhD out of University of Washington, teaching in Vancouver. He liked the fact Canada had converted to metric and felt it was a much better (logical) system. I said in most situations what he said was true. In Canada because we rub shoulders so much with Americans particularly through the media, we have to be bilingual (no, not French and English) in metric and imperial.

Certain measurements came out of usage, so we know what one pound is and to order one pound of hamburger in Canada you would probably ask for 500 grams of meat (this is actually slight more than one pound). So with metric in the butcher department we use a longer number of three digits to do the job of one digit. Its easier to say I want a half a pound of hamburger than say 250 grams.

This is the same for me when adding numbers quickly in my head, I simplify the numbers so they are easier to work with rounded numbers are easier for me. So if I add 67 plus 91, I really say to myself, 70 plus 90. But 70 is 67 + 3 and 90 is 91 - 1. And if when I add to a number, then I know in the answer of the addition I have to subtract, and if I subtract a number I know I have to add. So 70 + 90 is 160. 160 - 3 is 157 and 157 + 1 is 158. Needless to say I do this very quickly.

So I think the decimal system is more confusing that degrees, minutes, seconds because that is how time is broken down and its a very familiar paradigm in our heads.

 

[oguidry]

My Simrad can display degrees, minutes, and seconds as described above with a resolution of 0.1 seconds.

It can also display degrees and minutes with minutes to the third decimal point as in N 32-23.974.

It is easy to toggle back and forth.

The USCG communicates with its assets on VHF channel 1021, previously called 21A. There is a fair amount of traffic on this channel because small boats have to report their ops and position to Sector or Station every 30 minutes. If you scan 1021 (21A) and listen to the USCG, you will get a good sense of how they communicate position in your area.