Lat and Long Notation...................whats best

Fascadale

Fascadale

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What is regarded as the best way for leisure boating navigators to express Lat and Long?

In RYA publications you get Lat and Longs like 56˚ 22'.55 N 002 24'.65 W whereas my plotter would say 56˚ 22.55" N 2˚ 24.65' W

If we accept that seconds are now to be expressed as a decimal part of a minute where does the minute symbol best go? And what about the zeros in front of the 2, what purpose are they serving and why not a zero in front of the 56?

I have also seen decimal seconds written as say 33'.40 W or 44'.50 W: if it is a decimal what is the final zero for?
 
To take one part of your question.
As the maximum Latitude is only 90º, it would seem very eccentric to use three figures to express the degrees.
Longitude does often need three figures.
 
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In your first example you give the plotter as saying 22.55" N but 24.65' W. This seems inconsistent. Is this right?.

I don't think that it matters which notation is used so long as the meaning is clear. So far as I know, decimal fractions of a minute or never used in ordinary life, so confusion is unlikely.
 
NormanS has it right.

The leading 'zeros' ahead of the single-digit Longitude degrees numeral are intended to avoid ambiguity. Three-figure notation is specified, for that reason, in long-established international communications protocols, from the days of radio operators, and are still valid today. Similar applies to two-figure notation for Latitude degrees numerals - to avoid ambiguity and error.

We are expected to use the same concept/standards when writing and speaking of Degrees of Bearing i.e. 'Zero Three Four Degrees' rather than 'Thirty Four'. Every now and then, it really matters.... Especially when those whose first language is not English are trying to write down the details of a crackly Emergency Message. They are trained to expect a specific format - and you ought to have learned what that is, when you did your training for your legally-required Restricted VHF/License To Operate Certificate.... You do have one of those, don't you? You don't just burst into broadcast without a care in the world, or a thought, do you? ;)

Of course, some armchair admiral will burst into print on 'ere to sound off that he's always done it 'his way', and how he's never had a problem in 'scores of years sailing all the seas and oceans man and boy', and how his notion is best, and everyone else ....
 
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Points to consider are:
1. Unambiguity
2. Lack of likelihood of confusion by the navigator
3. Lack of likelihood of confusion by someone else over the radio, eg the CG

There are also conventions used in engineering about numbers of figures after the decimal point.


Degrees: To write down degrees I think you should always do two figures if Latitude, 3 figures if Longitude (and three figures if a bearing), padding with leading zeros if required. It probably doesn't matter if you only use two figures for longitude as the possibility of error is low around European waters as the first figure will always be zero, but assuming one aims for generality 3 is better practice. Follow with the degree symbol, °. So 52°, or 005°.

Minutes: GPS sets use degrees and minutes, with decimal fractions of minutes, and this is displayed on the VHF DSC radio. It's also what is contained in the NMEA sentences. So doing it this way satisfies 2 and 3 above. Put the ' sign after the last decimal as then it's quite unambiguously decimal fractions of minutes. Pad with zeros if required, so 47.236' or 04.50'.

Seconds: Do not use in marine(1) navigation. They are not displayed by the GPS and not commonly used (I never heard them used on the VHF for instance). Nor are they displayed on the VHF's display, nor are they used in the NMEA sentences.

Why have extra trailing zeros on decimals, like 34.20? As far as I know there is no navigational convention, but in engineering there is a difference between 1.21 and 1.210: the implied tolerance or accuracy is +/- some fraction of (eg 0.5x) the last digit, so 1.21 would be between 1.205 and 1.215 for instance(2). I suppose that one would thus assume the same with positions, but am not entirely sure about this point. Finally, while logical, I think it could make for confusion if one were to use a different number of significant figures for lat and long.

So overall: 23° 04.53' N, 008° 46.90' W

Edit:
(1) But seconds are still used in terrestrial surveying I believe.
(2) The BSI now deprecates this practice, but nonetheless it used to be common.
 
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Far be it for me to contradict an RYA publication, but 22'.55 looks wrong to me, and is mathematically incorrect. You would say "twenty two point five five minutes" not "22 minutes point five five".

There's my tuppenny worth.
 
Thank you all for the very helpful replies: what a busy Monday morning we all seem to be having.( I've even found time to do an online RNLI survey)

I'm happy with the explanations for the zeros and the final zero in the two decimal places.

I too think that the minute sign should go after the last decimal thus avoiding any ambiguity.

Is there any explanation then for the RYA convention of putting the minute sign before the decimal point as in 56˚ 22'.55 N 002 24'.65 W
 
ronsurf said:
Far be it for me to contradict an RYA publication, but 22'.55 looks wrong to me, and is mathematically incorrect. You would say "twenty two point five five minutes" not "22 minutes point five five".

There's my tuppenny worth.
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Thank you, and I wish I had realised that before I posted my Lat/Long in my signature. Caused some confusion, and head-scratching.
Entirely logical - when you think about it, especially when the scale (on sides of chart) do not show seconds, but 10ths of a minute.
 
If I think back far enough I can just about remember reading a theodolite to 1/10th of a second and writing it all down in pencil in a notebook. No wonder we repeated all angular measurements at least three times.
 
ronsurf said:
Far be it for me to contradict an RYA publication, but 22'.55 looks wrong to me, and is mathematically incorrect. You would say "twenty two point five five minutes" not "22 minutes point five five".

There's my tuppenny worth.
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It's quite common in my industry to record say 1.5 Megohms as 1M5, but to have both the unit and the decimal point seems unusual.

The thing with trailing zeros is quite important if you're reading off an NMEA string or something, the leading and trailing zeros effectively put a digit in every box in a form.
 
This thread http://www.ybw.com/forums/showthread.php?362558-Navigation-Position-Format went into it all in great detail. There is an international standard (ISO 6709) which isn't really for human communications, but I gave details of a simple, widely used and unambiguous format for latitudes and longitudes in the last post.

If you want clarity in written representations, then the forms

ddd.dddd (degrees and decimal degrees)
ddd mm.mmmm (degrees and decimal minutes)
ddd mm ss.ssss (degrees, minutes, seconds and decimal seconds)

are completely unambiguous and in widespread use.

Of course, the addition of the degrees, minutes and seconds symbols as appropriate will make it clearer.

Although as navigators we are used to using the suffixes N and S or E and W to indicate the hemisphere concerned, it is more usual to indicate it by giving the number a sign; positive for N and E, negative for S and W. Naturally, most of my work involved both being negative! The sign convention is chosen to simplify navigational and geographic calculations.
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I was taught to say verbally 'minutes' before the decimal bit, eg:

"Fife one degrees tree seven minutes decimal fife north" would be a sample transcript. Don't know if it's right or wrong?
 
oldbilbo said:
We are expected to use the same concept/standards when writing and speaking of Degrees of Bearing i.e. 'Zero Three Four Degrees' rather than 'Thirty Four'. Every now and then, it really matters.... Especially when those whose first language is not English are trying to write down the details of a crackly Emergency Message. They are trained to expect a specific format - and you ought to have learned what that is, when you did your training for your legally-required Restricted VHF/License To Operate Certificate.... You do have one of those, don't you? You don't just burst into broadcast without a care in the world, or a thought, do you? ;)
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A pedant writes ...

It's quite legal to send an emergency message, crackly or not, without a VHF licence. In those circumstances, though, I suspect the broadcaster would have quite a few cares in the world, and certainly one big one.
 
And can anyone think of a situation where it might be appropriate to give a boat's position to more than one decimal place? (i.e. 1/10th of a minute or about 200 yards.) All too often you hear people giving three decimal places ove the vhf! Even MCA navigation warnings often give the location of a hazard to two decimal places and then ask for a wide berth.
 
DJE said:
And can anyone think of a situation where it might be appropriate to give a boat's position to more than one decimal place? (i.e. 1/10th of a minute or about 200 yards.) All too often you hear people giving three decimal places ove the vhf! Even MCA navigation warnings often give the location of a hazard to two decimal places and then ask for a wide berth.
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Yep... a few seasons ago, CliveG and I left Ramsgate for the Orwell, and found stupidly thick fog.... could barely see the bow... we were going through Foulgers gat, and they'd just moved the bouys and neither of us had the new position.... I found it by radar, and then called Clive (who didn't have radar) with the exact location.... if we'd only worked to an accuracy of 200yds, you might a well have been 2nm off.... but that's the only time!
 
DJE said:
And can anyone think of a situation where it might be appropriate to give a boat's position to more than one decimal place? (i.e. 1/10th of a minute or about 200 yards.) All too often you hear people giving three decimal places ove the vhf! Even MCA navigation warnings often give the location of a hazard to two decimal places and then ask for a wide berth.
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Yes, a friend "found" an uncharted, and previously unknown rock, 0.5m below LAT, and sent me its position. If I'd known that the datum that he was using was WGB84, while I was on OSGB36, I would have known precisely where the rock was. The position given was halfway up the hillside.:D
 
ronsurf said:
Far be it for me to contradict an RYA publication, but 22'.55 looks wrong to me, and is mathematically incorrect. You would say "twenty two point five five minutes" not "22 minutes point five five".

There's my tuppenny worth.
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Sorry, but your 2p is worthless:)

You say: " ... degrees, two-two minutes decimal fife-fife ..."

[Later] I see others agree.
 
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