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.

Does this help you with your question? 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]

Originally Posted by 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.

[SteamWake]

Originally Posted by mookiemookie

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]

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).

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.

[neumanf15]

Originally Posted by Rockin Robbins

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!

[Frederf]

That's where Atlantis is, 95°N 187°W

[Rockin Robbins]

Originally Posted by Frederf

That's where Atlantis is, 95°N 187°W

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

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

[leovampire]

[SteamWake]

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