1° of latitude bigger than 60nm?

[seafarer]

Originally Posted by Munchausen

Where did you read that? Last I heard, Mather AFB taught "meridian arc" navigation until it (the Nav school) was closed down.

:hmm: Assuming by "meridian arc" you mean using a pair of dividers to measure distance (nautical miles) using the tic marks along the longitude lines of an aeronautical chart.

As to the original question, the game map is laid out in squares ... approximately 64.7 nm on a side (which is suspiciously close to 120 km). For centuries, map makers have been trying to figure an accurate way of sticking a round earth (all of it ... or at least as much of it as is displayed in the game) on to a flat piece of paper ... I'd be more than a bit surprised if the SH4 dev team finally figured out how to do it.

I have no idea how the US air force teaches navigation. But the US Department of Commerce (National Bureau of Standards) and the US Department of Defense both adopted the international standard nautical mile of 1852 metres, effective July 1, 1954. Prior to that, it was one minute of meridian arc at 48°N latitude.

The research ships and NOAA ships I used to go to sea on in the 1990's all used the international standard nautical mile. It has been the standard for maritime navigation the world over for a very long time. As a researcher, we tended to prefer to use UTM (Universal Transverse Mercator) instead, since it was more precise and easier to work with, and it meshed better with the short baseline acoustic navigation we used to have to use with our submersibles and robotic vehicles (we'd place a transponder grid on the sea floor, align it to a UTM chart, and then just work in decimal coordinates and distnaces, based on acuostic interrogations of the grid from the surface and/or the subs).

The international standard nautical mile had previously been adopted by most of world, other then the US, after 1929 (the standard came out of the Monoco International Extraordinary Hydrographic Conference of 1929).

[Munchausen]

Originally Posted by seafarer

As a researcher, we tended to prefer to use UTM (Universal Transverse Mercator) instead, since it was more precise and easier to work with, and it meshed better with the short baseline acoustic navigation we used to have to use with our submersibles and robotic vehicles (we'd place a transponder grid on the sea floor, align it to a UTM chart, and then just work in decimal coordinates and distnaces, based on acuostic interrogations of the grid from the surface and/or the subs).

That's a bit like apples and oranges. "Navigating" relative to a transponder (or any fixed point) is like drawing a treasure map ... ten paces west, thirty-seven paces east, twelve paces past the two palm trees, etc. Navigating across the globe and fixing your position via celestial navigation is a whole different kettle of fish.

Admittedly, I can certainly understand the use of your standardized nautical mile with electronic systems such as an INS or GPS. But there is really very little difference between a GPS plot and the PPOS in SH4. They both use computers to maintain an accurate update. Same as with modern ships. Same as with an F-16. In the old days (compared to civilian counterparts, the military was much slower installing electronic navigation systems), preplanning and DR navigation required the use of ONC, JNC and TPC charts ... all of which used the old "1 minute latitude = 1 nautical mile" definition.

Nowadays, the equipment does the tracking. But navigators were still doing it, via the basics, long past 1950.

[seafarer]

Originally Posted by Munchausen

That's a bit like apples and oranges. "Navigating" relative to a transponder (or any fixed point) is like drawing a treasure map ... ten paces west, thirty-seven paces east, twelve paces past the two palm trees, etc. Navigating across the globe and fixing your position via celestial navigation is a whole different kettle of fish.

Admittedly, I can certainly understand the use of your standardized nautical mile with electronic systems such as an INS or GPS. But there is really very little difference between a GPS plot and the PPOS in SH4. They both use computers to maintain an accurate update. Same as with modern ships. Same as with an F-16. In the old days (compared to civilian counterparts, the military was much slower installing electronic navigation systems), preplanning and DR navigation required the use of ONC, JNC and TPC charts ... all of which used the old "1 minute latitude = 1 nautical mile" definition.

Nowadays, the equipment does the tracking. But navigators were still doing it, via the basics, long past 1950.

I was never arguing with you, but you're talking about the practical nature of plotting on a chart. My original comment was simply that, regardless of just how one plots courses on a chart, the official standard definition of a nautical mile is not one minute of arc, and has not been for a long time, both in the US and elsewhere. That standard happens to be so very close to one minute of arc, that one may practically use either on a paper chart, but it does not change the fact that, officially, one nautical mile is exactly 1852m (which is something like 0.99???... mean meridian arc minutes).

And, just for the record, ground truthing a 1000mx1000m transponder grid in 3500m of water so you know where it is on the surface of the globe is a bit more involved then a kid's treasure map exercise. Especially when you want to come back to the exact same spot on the sea floor (within a metre or so anyway) in a few years time :p

[Frederf]

Looks like 2000x2000m grid (checked in metric mode). 1852m it's not.

[Munchausen]

Originally Posted by seafarer

That standard happens to be so very close to one minute of arc, that one may practically use either on a paper chart, but it does not change the fact that, officially, one nautical mile is exactly 1852m (which is something like 0.99???... mean meridian arc minutes).

So it is. Even my 1964 Information Please Almanac agrees with you. 1 nautical mile = 1852 meters = 6076.097 feet ("in most countries"). Ergo, 60 nautical miles = 111,120 meters (111.12 km) ... pretty much what my old air navigation computer comes up with. And, therefore, 111.12 km = 1 degree latitude.

:hmm: But celestial navigation is complicated enough without having to also convert back and forth between nautical miles and kilometers.

The thing is, airspeed indicators don't display KPH ... they display knots. Leastwise, they did when they were all analog. And in SH4, all speeds are displayed in knots. So, if anything, your official standard was a bit of a red herring. And I took the bait.

And, just for the record, ground truthing a 1000mx1000m transponder grid in 3500m of water so you know where it is on the surface of the globe is a bit more involved then a kid's treasure map exercise. Especially when you want to come back to the exact same spot on the sea floor (within a metre or so anyway) in a few years time :p

If you'd buried a couple million dollars worth of Spanish silver, I doubt you'd think of the treasure map as kid-stuff.

[Sailor Steve]

Originally Posted by Munchausen

Even my 1964 Information Please Almanac agrees with you.

As does what I consider the most important source of all: The American Practical Navigator, the acknowledged (American at least) handbook on all things nautical.