Different numbers for "Seconds" in Lats and longs?

[StuM]

Originally Posted by OldFrog75

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.

The information most readily available on the GPS is whichever the user has configured the GPS for.

The information most readily available on a paper chart is decimal minutes.

[StuM]

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).

Interesting take on it, but that's not what I understand happened at all.

According to this article, there was no position data:

http://www.langleysquadron.com/uploa...nd_devices.pdf

And according to this one:

Maker of GPS device sued in yacht race crash that left 4 sailors dead - latimes

"Court documents state that about 1:30 a.m. April 28, 2012, the Aegean somehow became disabled. When the SOS emergency function on the Spot Satellite GPS Messenger was activated, emergency responders were never notified, the complaint alleges."

[jackdale]

Originally Posted by StuM

The information most readily available on the GPS is whichever the user has configured the GPS for.

As well, make sure your GPS (not chartplotter) is configured for the same horizontal datum which your chart(s) use(s).

[jackdale]

Originally Posted by StuM

http://www.langleysquadron.com/uploa...nd_devices.pdf

Should be required reading. SPOT is not an replacement for either PLBs or EPRIRBs.

[estarzinger]

Originally Posted by StuM

Interesting take on it, but that's not what I understand happened at all."

Stu, I was on the accident investigating team. I have all the raw data and inputs.

There was a sos message sent. With a time stamp, but no location data. However the spot had been set to auto position reporting (I think every 10 minutes), so there was also a track position (with valid location data) from only a short time before the sos message (I think 4 minutes).

There were further problem(s) with geos internal protocols, which caused all this to be reported hours after it should have been. But those are a bit off topic since the thread is about location formatting.

I have copies of all the spot messages and all the communications with the family, Rc and uscg and all of gros's internal protocols . . . As I was the team member specifically designated to dig into the spot aspect of the incident.

[jackdale]

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).

As promised.

I wouldn’t say that there is necessarily a standard, Jack. In the world of engineers, most would likely prefer decimal degrees which is what you have indicated below. The main reason for this is it is easy for them to understand and use in calculations.

Surveyors often use a combination of Degrees, min, seconds and Decimal degrees. We always indicate bearings and azimuths as Deg,min, sec. latitude and longitudes are often provided in both dms and dd.

The statement below is true – it’s the preferred method when it comes to the ISO standard but we use whatever our end user requires.

[hellosailor]

You could say the ISO standard is just that: Words on paper. There are ISO9000 standards for manufacturing and businesses, and when properly implemented they can be a great thing, but sailors tend to follow TRADITION unless someone has a Real Damned Good Reason for change. And since we all (ahem) already know, expect, and use the old DDD.MM.SS format...even if the ISO standard gives better precision, we generally can't use it. No one wants or needs to know their vessel position with two centimeters, really, do they? And if it takes a few less data bits to record or transmit, a little less bandwidth...we're already working with what we've got, aren't we?


So, "engineering" formats, for ships? Maybe first they could promote an ISO standard for a bottom paint that worked.(G)

[Stu Jackson]

Interesting banter.

OK, I'll giver it a go.

It simply doesn't matter.

Why?

Which are "better?":

miles, kilometers, nautical miles, feet, inches, fathoms, cables...

They are all a measure of distance.

Analogous to this.

And meaningless differences in the real world, except for misusing or misinterpreting them.

[hellosailor]

"10ths of minutes (AKA cables). " So the length of a Canadian Cable varies with whether it is being used for latitude or longitude, and at what point on the sea or earth?


Minutes, after all, unless being used as arc radial measurements, are of varying lengths, significantly varying lengths, at the equator and near the poles.


I find fathoms useful, in that the "average" man standing with arms fully outspread, will have about a six foot spread, so one "armspread" of line will often be close to a fathom.

[jackdale]

Originally Posted by hellosailor

"10ths of minutes (AKA cables). " So the length of a Canadian Cable varies with whether it is being used for latitude or longitude, and at what point on the sea or earth?


Minutes, after all, unless being used as arc radial measurements, are of varying lengths, significantly varying lengths, at the equator and near the poles.


I find fathoms useful, in that the "average" man standing with arms fully outspread, will have about a six foot spread, so one "armspread" of line will often be close to a fathom.

A cable is one tenth of a nautical mile, which is one minute of latitude on a chart.

[jackdale]

Originally Posted by Stu Jackson

Interesting banter.

OK, I'll giver it a go.

It simply doesn't matter.

Why?

Which are "better?":

miles, kilometers, nautical miles, feet, inches, fathoms, cables...

They are all a measure of distance.

Analogous to this.

And meaningless differences in the real world, except for misusing or misinterpreting them.

Rather the question is what is "conventional."

As we all know.

In the marine world, distances are measured in nautical miles, speeds (boat, wind, current) in knots.

Most of the world using meters, rather than fathoms and feet, for depths. Which why we have to read title blocks.

[Stu Jackson]

Originally Posted by jackdale

Which why we have to read title blocks.

So very important, so little understood. Great point.