Thread: Which way do I go

1. Originally Posted by Gun Nut
Originally Posted by bilby
Originally Posted by Gun Nut

A Great Circle is not a curved path.
Say that again. Slowly.

Any straight path that starts on the surface of a sphere leaves that surface (either it's a tangent that heads off into space, or a chord that tunnels into the ground).

All paths that are bound to the surface of a sphere are curved.
Besides that fact that I am a private pilot with an instrument rating, I also am a fan of cartography. I love maps. So I know a little more than a little about this.

AAAA GRRRRREAT CIRRRRRRRRRCLE. There nice and slow for you.
"circle is in the name"... great argument Airplanes fly great circle paths... so how can they ever deliver passengers to any destination??? If they fly a CIRCLE, then they always end up where they started!!!! Air travel is a lie!

Look at a globe. Then look at a map. Compare the size of Greenland between the two. I guess you would be completely shocked to discover that Greenland looks GIGANTIC on the map compared with the globe.... ever wonder why? It's because globes are spherical and maps are flat planes. Well how can you draw a map that can be folded up and put in your pocket or included in a book of flat pages? It's called making a projection... a way of making the "edges" of the map spread out relative to the middle of the map so the scale can be consistent across the entire map. This makes land masses appear larger at the edges than in the middle... that is just geometry.. projecting a curved surface onto a flat plane.
So, how can pilots navigate using flat maps? The solution is called flying a "great circle". It's just a name, they don't really fly in circles. They fly a straight line from point A to point B... when re-drawn on a globe would be a straight line.. but when drawn on a flat map it appears to be a curve (to the north, if located in the northern hemisphere).

That is what a great circle is... don;t let the label confuse you.

edited to add: aren't you a submariner? or am I thinking of another poster? dude, this is very basic Nautics (aero or otherwise). whether you are under, on, or over the water... basic navigational principles are all the same.
Your condescension is unwarranted. A great circle is a circle centred on the centre of the Earth, and is very definitely a circle. A great circle route is the shorter of the two arcs of a great circle that passes through both origin and destination.

And a straight line route between two points on the surface of a sphere requires a tunnel. If you don't know what a straight line is, then you have no business discussing geometry.

And I have already, in this thread, explained both that fact, and in detail what Mercator's projection is, what it's good for, why it's shit for understanding anything else about geography (including but not limited to the relative areas of various land masses), and how it can be used for simplifying navigation but doesn't provide optimal shortest routes (instead giving constant bearing routes).

In summary, your post pointing out my errors is erroneous in every detail, and a simple reading of my other posts in this thread would have provided you with that information, and could have saved you from making a collosal tit of yourself.

You are also wrong about me being a submariner. But at least that error's correction would have required reading more than just my posts in this thread alone.

2. Originally Posted by Gun Nut
Originally Posted by Jokodo
Originally Posted by Gun Nut

Besides that fact that I am a private pilot with an instrument rating, I also am a fan of cartography. I love maps. So I know a little more than a little about this.

AAAA GRRRRREAT CIRRRRRRRRRCLE. There nice and slow for you.
"circle is in the name"... great argument Airplanes fly great circle paths... so how can they ever deliver passengers to any destination??? If they fly a CIRCLE, then they always end up where they started!!!! Air travel is a lie!

Look at a globe. Then look at a map. Compare the size of Greenland between the two. I guess you would be completely shocked to discover that Greenland looks GIGANTIC on the map compared with the globe.... ever wonder why? It's because globes are spherical and maps are flat planes. Well how can you draw a map that can be folded up and put in your pocket or included in a book of flat pages? It's called making a projection... a way of making the "edges" of the map spread out relative to the middle of the map so the scale can be consistent across the entire map. This makes land masses appear larger at the edges than in the middle... that is just geometry.. projecting a curved surface onto a flat plane.
So, how can pilots navigate using flat maps? The solution is called flying a "great circle". It's just a name, they don't really fly in circles. They fly a straight line from point A to point B... when re-drawn on a globe would be a straight line.. but when drawn on a flat map it appears to be a curve (to the north, if located in the northern hemisphere).

That is what a great circle is... don;t let the label confuse you.

edited to add: aren't you a submariner? or am I thinking of another poster? dude, this is very basic Nautics (aero or otherwise). whether you are under, on, or over the water... basic navigational principles are all the same.
Sorry to blunt, but you are making it Sound as though you haven't fully understood the globe thing. A great circle is called a circle because it is in fact a circle centered at the earth's centre - or more accurately an ellipsis. It is called great because any larger circle/ellipsis larger than it will take you off planet - as will a straight line.
..on a globe. You don't need a great circle on a globe... every shortest path between two points on a globe is a great circle, by definition. no one talks about "great circles" on a globe... just like you don't talk about what great resolution the scenery is in when you are looking at it in real life (not an image on a screen). "resolution" refers to the level of detail of a projection of an image onto a flat screen. when you are not talking about viewing it on a screen, "resolution" is nonsense... just like great circles on a globe.... on a flat map a great circle is simply what the shortest path between two points looks like, and is curved because flat maps are deformed representations of the surface of the earth. that's it.. it's not so complicated.
When you are in a hole, stop digging.

3. Originally Posted by bilby
Originally Posted by Gun Nut
... every shortest path between two points on a globe is a great circle, by definition.
When you are in a hole, stop digging.
Heh, what an appropriate admonition, given that the shortest distance between any two points on the surface of a sphere is through the sphere itself. Yes, kids of America, the shortest route to China is to dig a hole. It's a little more difficult than transiting an arc on the surface of the almost-a-sphere of earth, but it's SHORTER!

ETA: Projections are interesting

4. Originally Posted by Elixir
Originally Posted by bilby
Originally Posted by Gun Nut
... every shortest path between two points on a globe is a great circle, by definition.
When you are in a hole, stop digging.
Heh, what an appropriate admonition, given that the shortest distance between any two points on the surface of a sphere is through the sphere itself. Yes, kids of America, the shortest route to China is to dig a hole. It's a little more difficult than transiting an arc on the surface of the almost-a-sphere of earth, but it's SHORTER!
It's better than that; It's fast and (almost) free!

A straight line tunnel between any two points on the surface of the Earth, evacuated and made frictionless (maglev? superconductors?) can get you from one end to the other in about 90 minutes, purely on gravitational acceleration.

That's a pretty good journey time for most trips - cf. over 20 hours from Sydney to London by subsonic jet.

Of course, drilling and maintaining an airtight and evacuated tunnel in a completely straight line through the mantle (and for some trips, the core) of the Earth may prove to be a little tricky from an engineering perspective. Some kind of Unobtanium tunnel lining may be needed to keep the magma out. And unless you want 90 minute char-broiled passengers, some thermal insulation may also be in order.

5. I do have a better appreciation for this than before.

For example, if I mark two points on a map (‘a’ and ‘b’ for a beginning point and ending point) and draw a straight line between the two, and then, mark the half way point as ‘c’, and then, do the same on a globe, then although points ‘a’ and ‘b’ will be the same for both the map and the globe, point ‘c’ (the half way point) will be different.

6. It is apparent from the discourse 'you can't get there from here'. As the saying goes.

GPS is a good thing for some people. For any ex boy Scouts, which side of a tree does moss grow on typically?

7. Originally Posted by steve_bank
It is apparent from the discourse 'you can't get there from here'. As the saying goes.

GPS is a good thing for some people. For any ex boy Scouts, which side of a tree does moss grow on typically?
The south side - because that side never gets the full sun on it.

Of course, I was never a boy scout; And I live in the Southern Hemisphere - in the Northern Hemisphere the moss would predominantly grow on the north side of trees.

8. Even though I have always heard all my life the "survival tip" of navigating by tree moss' preference for the north side of trees, I have found it useless in the area of the country I live in. The forests are dense so no side of trees get regular sunlight. Also humidity isn't that high so few trees have moss on the trunks and the ones that do have some sparse moss have it on all sides. A compus or even the sun's position would be more useful but only if the best direction to go to get out of the forest is first known.

9. Originally Posted by skepticalbip
Even though I have always heard all my life the "survival tip" of navigating by tree moss' preference for the north side of trees, I have found it useless in the area of the country I live in. The forests are dense so no side of trees get regular sunlight. Also humidity isn't that high so few trees have moss on the trunks and the ones that do have some sparse moss have it on all sides. A compus or even the sun's position would be more useful but only if the best direction to go to get out of the forest is first known.
Yeah, if you want to know which way is north, the position and length of shadows is likely your best indicator.

But frankly, if you are lost, there's more to be said for topology than orientation. Who cares whether you are facing north or south, if you don't know where anything else is in relation to your position?

If you're lost, you are best off making yourself visible to those who are not lost, rather than moving - any significant movement most likely gets you further from your last known position, and just increases the search radius for rescuers.

But the best strategy really does depend on your situation. If you are stranded in the outback, staying with your vehicle is almost always the best bet. It's a LONG way to the nearest tree, or water source, or anything else, in many places. And your car is much easier to locate from a rescue aircraft than your body is.

10. Originally Posted by fast
I do have a better appreciation for this than before.

For example, if I mark two points on a map (‘a’ and ‘b’ for a beginning point and ending point) and draw a straight line between the two, and then, mark the half way point as ‘c’, and then, do the same on a globe, then although points ‘a’ and ‘b’ will be the same for both the map and the globe, point ‘c’ (the half way point) will be different.
And in many cases, c will be different for two different maps

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