1° of latitude bigger than 60nm?

[Frederf]

Why are degrees of latitude larger than 60nm on the map? I thought a minute was a nautial mile, but when I measure distances between the vertical lines they aren't the proper size. Noticed this while trying to run "real nav" mod.

[Rockin Robbins]

Things get complicated because of the Earth is not a sphere but an oblate spheroid. That means that it bulges slightly at the equator and the poles are slightly flattened by the centrifugal force of the earth's rotation about its axis. So a degree of latitude actually varies in length with latitude.

At 29º a degree of latitude is 59.846 nm. At 75º it is 60.269 nm and at 95º it is 60.305 nm. So the closer to the equator you are the shorter the definition nautical mile should be. Since we fixed that dimension, the closer to the equator you are, the shorter distance one degree of latitude is!

For those who are wondering what on Earth (;)) we are talking about
Unlike other imperial measurements, the nautical mile derives its definition from a convenient measurement on the Earth itself. One nautical mile is supposed to equal one minute of arc in latitude anywhere or in longitude at the equator. As usual with such definitions, and similarly to the meter, inaccuracies in our ability to measure the dimensions of the Earth at the time such standards were established converted the sensibly defined unit from one verifiable by measuring the Earth itself to just another arbitrary unit! Although a nautical mile is somewhat close to a minute of arc (60 minutes equals one degree which should equal 60 miles and hence this conversation), it is not, and so is no better than the imperial foot in being a "scientifically rational" unit.:ping:

Does this help you with your question? :down: No!

[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).

[mookiemookie]

I'm going to go with the "it's the type of map projection" hypothesis for $500, Alex.

[SteamWake]

Uhh the 'world' in SH4 is flat.

[mookiemookie]

Uhh the 'world' in SH4 is flat.

I'm no cartography wizard, but I thought that the map projection in the game was scrunched up at the upper latitudes and stretched out at the middle ones, and that was my guess as to why the values were off. I could be wrong.

[SteamWake]

Uhh the 'world' in SH4 is flat.

I'm no cartography wizard, but I thought that the map projection in the game was scrunched up at the upper latitudes and stretched out at the middle ones, and that was my guess as to why the values were off. I could be wrong.

Me either but I do understand conical projection but I really dont think this was done in SH4. I could be wrong though.

Early attempts at using real world type navigation were found to be futile due to the 'abberations' in the projections.

[Munchausen]

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).

:o 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.

[Frederf]

Yeah I've read a bunch about latitude and the definition of a nautical mile previous to his. Is the Earth that oblate to be something 7.8% or more bigger than the standard nm... that's a big difference. I figured the Earth was oblate to the tune of 0.5% to 1.0%.

At 29º a degree of latitude is 59.846 nm. At 75º it is 60.269 nm and at 95º it is 60.305 nm. So the closer to the equator you are the shorter the definition nautical mile should be. Since we fixed that dimension, the closer to the equator you are, the shorter distance one degree of latitude is!

56.9846.... 60.269... those numbers are a lot closer than 64.7. I can't see why 64.7 is some kind of compromise between those two.

I'm no cartography wizard, but I thought that the map projection in the game was scrunched up at the upper latitudes and stretched out at the middle ones, and that was my guess as to why the values were off. I could be wrong.

This seems most likely. When you're a SH4 dev and you throw the real globe out the window, you lose your appeal to reality to help you make the game. I wonder if this is why sextant navigation is so inconsistent in the game... perfectly rendered sky but with an alien earth under it?

[Rockin Robbins]

Nope, it's clear that the numbers in the game are not caused by the Earth's dimensions. One degree would be smaller than 60 nm, not larger as in SH4, if that were so. I just thought the irrelevent facts I provided were interesting even though they did nothing to help answer your question. :88)

[neumanf15]

At 29º a degree of latitude is 59.846 nm. At 75º it is 60.269 nm and at 95º it is 60.305 nm.
When did they add another 5º of latitude to the Earth? Last I checked there were only 90º each way (North and South). I'm always the last to hear these things! :doh:

[Frederf]

That's where Atlantis is, 95°N 187°W

[Rockin Robbins]

That's where Atlantis is, 95°N 187°W

Yeah! What he said! I should have typed 85º there, but that's kinda obvious. :oops:

Now I know what's north of the North Pole. Atlantis!

[leovampire]

http://static3.filefront.com/images/personal/l/leovampire/93141/nwpzphggec.jpg

[SteamWake]

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

[leovampire]

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]

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]

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).

:o 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]

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]

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.

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]

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

:arrgh!: 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]

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.