1° of latitude bigger than 60nm?

[leovampire]

Originally Posted by SteamWake

You cant fool me that was photo shopped (fisheye).... heh

The camera mod we made for ROW allows you to go up to 10,000 so you can see the curvature of the Earth with it.

[Pulver]

Originally Posted by seafarer

Note that the modern, albeit arbitrary, international standard definition is 1852 metres, exactly. The one minute mean meridian arc definition has not been applied in navigation in quite some time (since 1954 in the USA, since 1929 in most of the rest of the world).

What distorts everyone's beliefs even more today is the use of GPS and other electronic navigation tools. The arc minute (Nautical Mile) is now depeicted on many charts in 10ths of an arc minute as opposed to arc seconds, forcing the pureist navigator to have to convert scales.

For those interested, from 1978 until 1990 I was a navigator in the U.S. Air Force. Most charts used in mid-latitude ranges were Lambert Conformal projection which accounted for some distortion of the curvature of the earth. They also depicted clearly the convergence of longitude toward the poles. But that was using the JNC or Jet Navigation series of charts.

With the exception of the Great Lakes, and perhaps other areas of the planet I am not aware of, nautical navigation charts are projected as a transverse mercator, (or similar projection type) that gives the appearance of lines of Latitude and Longitude running at constant 90 degree angles (like Grid or like they were all lines having the properties of a Great Circle). As such with regard to arc minutes equalling nautical miles, regardless of the earth's natural distortion, and accounting for the relative low speed of a ship vs. an aircraft, the distance between latitudes remain unchanged. Chart error is compensated for at the time of the DR and Fix or Most Probable Position plot. That is of course if your GPS breaks. However, at least as of 2004, aboard U.S.S. Mobile Bay, even though the ships' director system was coupled to the the GPS, the Quartermaster still carried a plot as would have been done in the 1940's and earlier. And on the Quartermaster's chart, one arc minute equaled 1 nautical mile.

The only rule of navigation that I am aware of that relates degrees to miles and is somewhat in error is the 1 degree of course error equals 1 nautical mile of cross track displacement after travelling 60 nautical miles. The actual distance if I recall is something like 57.8 NM, but at 500 knots, it never made much difference to me.

[Frederf]

I don't see how fast one is going has much to do with anything? Curious how that works.

@leovampire: Yes the scene shows the curveture of the Earth, but the actual globe environment is flat. Think of the rendered 8,000m radius (or whatever, some mods are bigger) rendered environment as a performing theater stage on the back of a big semi truck that's free to drive over town. The stage is curved but the town is flat. Optical effects like the horizon dip and ships appearing half submerged at distance are because of the curveture of the stage. The town on the other hand is flat so driving around at 89°N takes just as long as at the equator.

[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.