Different numbers for "Seconds" in Lats and longs?

[hellosailor]

Well...actually the "correct" modern way to do mapping is to the ISO engineering standard, which would be DDD.ddddd that is, all in degrees, to five decimal points.


The math can be simpler, and the precision is higher, and the number of digits that has to be transmitted or recorded is lower.


Just don't expect any sailors to be doing it that way, we still think in terms of "a mile is a minute" and that's something awkward like 0.016666 degrees.

[StuM]

Originally Posted by OldFrog75

First off I think you need to double check your arithmetic since 192' is closer to 2 seconds than 1 second.

Actually 192' is 11,520 seconds.

Oh, sorry, I guess you meant feet, not minutes by that tick mark.

That's another reason why I prefer decimal and metric. Less room for confusion

[jackdale]

Originally Posted by StuM

Compare 17°17'17" to 17°17.17'

1 Minutes is 1852 meters
A second is 1/60th of a minute.
So seconds are accurate to the nearest 31 meters
Two decimal places is 1/100th of a minute.
Therefore accurate to the nearest 18.52 meters.

But that's not why I prefer it.

I just find it easier to visualise decimal second distances.
0.17 is ~340m (double the number and add ten)
And I can easily relate 340m to multiples of football fields, athletic tracks or whatever.

I have to put a lot more thought into "roughly how far away is 17/60 Nm?"

In the case I work in cables (as does the Canadian Coast Guard). A cable is close enough to 200 yards or 200 meters (although not precise) that I can usually judge that.

When anchoring, without the availability of radar, I use boat lengths - not very accurate or precise; but I have not swung into anyone (unless they anchored after me).

[StuM]

Originally Posted by hellosailor

Well...actually the "correct" modern way to do mapping is to the ISO engineering standard, which would be DDD.ddddd that is, all in degrees, to five decimal points.


The math can be simpler, and the precision is higher, and the number of digits that has to be transmitted or recorded is lower.


Just don't expect any sailors to be doing it that way, we still think in terms of "a mile is a minute" and that's something awkward like 0.016666 degrees.

If you want to follow a relevant ISO standard take a look at "ISO 6709 Standard representation of geographic point location by coordinates"
ISO 6709:2008 - Standard representation of geographic point location by coordinates

(If you want to waste $140)

Then come back and tell us the "correct" way according to that load of horsepuckey

Bottom line, there ain't no "correct" way. Use whichever common representation you prefer as long as others can understand it unambiguously. (Which is essentially what that "Standard" says).

[StuM]

Originally Posted by jackdale

In the case I work in cables (as does the Canadian Coast Guard). A cable is close enough to 200 yards or 200 meters (although not precise) that I can usually judge that.

When anchoring, without the availability of radar, I use boat lengths - not very accurate or precise; but I have not swung into anyone (unless they anchored after me).

Yep, even easier if you are used to visualising in terms of that distance - no need to double the number:

0.17 minutes = 1.7 cables

( I just find it easier personally to visualize in 100s of yards/meters. If I need to express it in cables, it's easy enough to halve it again )

[jackdale]

Originally Posted by StuM

If you want to follow a relevant ISO standard take a look at "ISO 6709 Standard representation of geographic point location by coordinates"
ISO 6709:2008 - Standard representation of geographic point location by coordinates

(If you want to waste $140)

Then come back and tell us the "correct" way according to that load of horsepuckey

Bottom line, there ain't no "correct" way. Use whichever common representation you prefer as long as others can understand it unambiguously. (Which is essentially what that "Standard" says).

I have asked a couple of squash friends who are geomatics engineers about that. I will post their response(s).

The "standard" used in the navigation programs that I teach is degrees, minutes, 10ths of minutes (AKA cables).

[OldFrog75]

Originally Posted by StuM

Absolutely.

Whilst precise, OF75's statement was not accurate.

I'm not convinced my statement was not correct:

Accurate - (of information, measurements, statistics, etc.) correct in all details; exact.
synonyms: correct, precise, exact, right, error-free, perfect;

"In the fields of science, engineering and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value"

Is not 0.025 minutes of latitude or longitude a more accurate measure of location than 1 or 2 seconds?

[StuM]

Originally Posted by jackdale

I have asked a couple of squash friends who are geomatics engineers about that. I will post their response(s).

The "standard" used in the navigation programs that I teach is degrees, minutes, 10ths of minutes (AKA cables).

The "standard" that I've use in the information systems that I design to store the data is decimal degrees. I also use that for machine transfer of data.

The "standard" that I use in user interfaces for data entry and display is the same one you use.

[StuM]

Originally Posted by OldFrog75

I'm not convinced my statement was not correct:

Accurate - (of information, measurements, statistics, etc.) correct in all details; exact.
synonyms: correct, precise, exact, right, error-free, perfect;

"In the fields of science, engineering and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's true value"

Is not 0.025 minutes of latitude or longitude a more accurate measure of location than 1 or 2 seconds?

Firstly, you are perhaps cheating a little ( ) by using 3 digits for decimal places compared to the two digits of seconds.

Secondly, it depends on what you are measuring. Which is more accurate when expressing 1/3 of a minute:
0.33 minutes or 20 seconds?
or even 0.333 minutes compare to 20 seconds?

[OldFrog75]

Originally Posted by StuM

Firstly, you are perhaps cheating a little ( ) by using 3 digits for decimal places compared to the two digits of seconds.

Secondly, it depends on what you are measuring. Which is more accurate when expressing 1/3 of a minute:
0.33 minutes or 20 seconds?
or even 0.333 minutes compare to 20 seconds?

Of course there are examples where the arithmetic works out between the two but given 1/100th of a nm is 60.76 feet and 1/60 of a nm is 101.27 feet, are not decimal minutes more accurate/precise than seconds?

As an side, being an American I'm lost when converting to meters. Hard enough to go from statute miles and mph to nautical miles and kts.

[DotDun]

Originally Posted by OldFrog75

Of course there are examples where the arithmetic works out between the two but given 1/100th of a nm is 60.76 feet and 1/60 of a nm is 101.27 feet, are not decimal minutes more accurate/precise than seconds?

As an side, being an American I'm lost when converting to meters. Hard enough to go from statute miles and mph to nautical miles and kts.

And seconds taken to 3 decimal places is more precise than minutes to 3 decimal places.

Whats your point?

[OldFrog75]

Originally Posted by DotDun

And seconds taken to 3 decimal places is more precise than minutes to 3 decimal places.

Whats your point?

I have never seen seconds taken to 3 decimal points on a gps device whereas minutes are always taken to 3 decimal points - at least that's the way it is on my Garmin.

The OP was questioning which is better for navigation seconds or minutes. It devolved into a debate about which is more accurate. Perhaps I misunderstood but I assumed it was in the context of what information would be readily available on someone's gps device (handheld or otherwise) or a paper chart.

[estarzinger]

So, true cautionary tale about mis-communication with all these different formats. . . . . In the Aegean incident (boat lost in Mexico with all hands), SPOT (or more accurately GEOS, which is SPOT's emergency signal subcontractor), gave out a position of the SOS, which the family, race coordinator uscg interpreted as d MM.MMM. They also gave out a time for the SOS message, which was interpreted as local time. They wasted a bunch of time looking at that location and time/drift rate. And then it was discovered that the stated location was in D.ddddd and the time was in UTC. And it became very obvious where the boat was (ashore on a rocky island).

[Wotname]

Originally Posted by estarzinger

So, true cautionary tale about mis-communication with all these different formats. . . . . In the Aegean incident (boat lost in Mexico with all hands), SPOT (or more accurately GEOS, which is SPOT's emergency signal subcontractor), gave out a position of the SOS, which the family, race coordinator uscg interpreted as d MM.MMM. They also gave out a time for the SOS message, which was interpreted as local time. They wasted a bunch of time looking at that location and time/drift rate. And then it was discovered that the stated location was in D.ddddd and the time was in UTC. And it became very obvious where the boat was (ashore on a rocky island).

Thanks for adding this to the thread A real world experience is always helpful in understanding the need combat mis-understanding / poor communicating skills.
A good reminder that stating the units of any measurement gives a far more complete understanding.

[StuM]

Originally Posted by OldFrog75

As an side, being an American I'm lost when converting to meters. Hard enough to go from statute miles and mph to nautical miles and kts.

Just think of them as yards instead of meters and treat 1 nm as 2000 yards. rather than 2000 meters.

That's near enough for the purpose - 2000 yards is actually a better approximation of 1 nm than 2000 metres.