Which coordinate system?

[svrevelations]

When giving your location position, which coordinate version is most used worldwide?

1. Decimal degrees,
2. Degrees, Decimal minutes,
3. Degrees, minutes, seconds.

[Sandero]

degrees, minutes and decimal minutes

[Snowpetrel]

DDD° MM.mm' is pretty universal at sea due to the paper charts being setup this way, athough the odd survey vessel or NTM occasionally wants to use secomds... Lat first, long second. Keep the placeholding zeros in.

[MarkJ]

I use degrees, decimal minutes.

Commercial shipping seems to use decimal degrees.

Shore based vhf users seem to prefer degress, mins, seconds.

I wish plotters like opencpn would have a button on the toolbar to instantly change it.


Mark

[tkeithlu]

There is good reason to use degrees and decimal minutes. Given that a minute of latitude is by definition a nautical mile, and the finagle factor for converting minutes of longitude into nautical miles is stable as long as you stay at about one latitude, resolving triangles- the length and direction of the hypothenus of the right triangle formed with two pairs of Lat-Lon locations - is something you can do roughly in your head (let's see, that's a 19 minute difference in latitude and a 10 minute difference in longitude, and I'm around 31 degrees north, so the cosine is about .85...). Given a few minutes, you can work it out precisely on your pocket calculator or graph paper. All that is much more complicated in decimal degrees or degrees, minutes, and seconds. You can also think in decimal minutes for distances - 1 degree lat is 6081 ft, 0.1 is about 600 feet, 0.001 is about 60 feet...Useful when you are setting up an anchor alarm.

Now if you want something really confusing, try navigating in National Grid, which FEMA insists on using - an attempt at assigning one kilometer squares and parts thereof unique letters and numbers. Aside from the impossibility of flat griding a spherical earth, the locations tell you absolutley zero about the relationship between two points.

[El Pinguino]

#2 Degrees, minutes, decimal minutes.

When you are out in your dinghy surveying some remote anchorage you may choose to work to three decimal places - however.....

If sending a position report from the central Pacific just stick to whole minutes.

If coastal give your position to one decimal place .

The reason being that the first decimal place is 1/10th of a mile or about 170 metres, the second is about 17 metres, and the third is 1.7 metres.

You still occasionaly hear wonks on vhf saying ' xx.xxx minutes' and just wonder if they have the vaguest idea what they are talking about and also which end of the boat they are refering to..

[wrwakefield]

Originally Posted by Revelations

When giving your location position, which coordinate version is most used worldwide?

1. Decimal degrees,
2. Degrees, Decimal minutes,
3. Degrees, minutes, seconds.

We find different sources require different coordinate versions, so we standardize to suit our own preferences.

Therefore we keep a coordinate system converter app on our smart phones. [There are many apps and many online converters as well...]

That way we can standardize all of our navigation systems to what we prefer, and quickly convert to what is needed by others.

An example is we use Degrees, minutes, seconds for ourselves, but need to convert to Degrees, Decimal minutes for our position update service [which we choose to manually update via a structured email.]

I think a built-in converter [vs. changing a preferences setting...] would be great in the navigation programs we use. [And some may have it and we just don't know about it...]

Meanwhile, our app does the trick for us.

In case this is helpful.

Cheers!

Bill

[barnakiel]

I believe I have heard and seen mostly degrees minutes decimals (dd mm.mx). This seems most common in Anglophile countries. I also believe this is what French CG uses in their DOM/TOM countries.

My own preference onboard is accidentally the same system. dd.dx is my second choice, only when pressed. I strongly dislike dd mm ss.

b.

[Paul L]

It depends on who you are reporting to. If it is a cruisers SSB net, then it should be dd mm N or S, ddd mm E or W. It does no good to go beyond this resolution and ends up with lots of miss heard numbers if add decimal decimal positions.

[El Pinguino]

The only place I have ever come across seconds of arc is in very old...as in 19th century ... navigation books such as Lecky's Wrinkles.. with one exception ... I have a post war French chart ( 50's?) of Detroit de Singapura(sp) which shows seconds.

I can imagine no practical use for them.

[svrevelations]

Thank you all!
That certainly clarified the issue for us - also a couple of thoughtful comments.

[Snowpetrel]

Originally Posted by MarkJ

I use degrees, decimal minutes.

Commercial shipping seems to use decimal degrees.

Not on any of the ships I ever worked on. Id get booted off the bridge quicksmart if I tried using decimal degrees. Deg, min, decimal mins all the time.

I think its pretty dangerous to start playing around with deg, min, sec. It gets far to easy to make a mistake and mix seconds with decimal minutes.


Sent from my SM-G930F using Cruisers Sailing Forum mobile app

[El Pinguino]

Originally Posted by Snowpetrel

Not on any of the ships I ever worked on. Id get booted off the bridge quicksmart if I tried using decimal degrees. Deg, min, decimal mins all the time.

Ditto

Apart from GE and similar my only dealings with decimal degrees has been when writing simple sight reduction programs for things like the old Sharp minicomputer thingos 30 odd years ago... you had to convert from degrees and minutes to decimal degrees *within* the program.

[StuM]

Originally Posted by El Pinguino

Ditto

Apart from GE and similar my only dealings with decimal degrees has been when writing simple sight reduction programs for things like the old Sharp minicomputer thingos 30 odd years ago... you had to convert from degrees and minutes to decimal degrees *within* the program.

Delorme Inreach mapping displays Lat/Long as D.dddddd° and elevation as M.mm meters ( i.e position in decimal degrees to the nearest 11cm and elevation to the nearest 1cm).

And Google maps display D.ddddddd (i.e. to the nearest cm)

The interfaces were obviously designed by programmers, not navigators

At least the Anchor Alert app that I use has degrees and minutes, but it shows D.MM.mmmmm and I doubt the accuracy of that last decimal place - at 1.8cm or 3/4 inch.

[mikeod]

Am i correct that deg min secs would be needed for celestial nav?