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rajeshrocks25
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Join Date: May 2009
Posts: 17

Great marine circle method

05/30/2009 2:44 AM

can we use the Great marine circle method for finding path between two points having distance between them less than 250 km

can u please tell what is the important of this method???
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TVP45
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#1

Re: Great marine circle method

05/30/2009 6:41 AM

You may use the great circle method for any distance on the earth's surface. It becomes more useful (that is, much shorter than straight line) with greater distances. When to use it is up to you, unless you're doing a navigational problem. That is when it's important.

If you need to understand the importance, purchase (or borrow) a globe. Try measuring great circle distances and straight line distances.

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rajeshrocks25
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Join Date: May 2009
Posts: 17
#4
In reply to #1

Re: Great marine circle method

05/31/2009 1:29 AM

i am in a bit of confusion ...

can u tell me how can we calculate the direction of the travel???

and can we change the direction with constraints on passing through certain locations??
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rajeshrocks25
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Posts: 17
#8
In reply to #1

Re: Great marine circle method

06/01/2009 6:50 AM

in my problem i am finding it difficult after few steps because the distance is getting decreased to such a extent that i am unable to get the accurate initial heading... is der any way out of it
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rajeshrocks25
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#9
In reply to #1

Re: Great marine circle method

06/01/2009 7:42 AM

i mean will it give better results if i maps the point s on to a sphere of smaller radius??

please reply i need help...
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TVP45
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#10
In reply to #9

Re: Great marine circle method

06/01/2009 8:12 AM

http://216.147.18.102/dist/index

is a calculator that might help.

What exactly are you trying to do?

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rajeshrocks25
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Join Date: May 2009
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#12
In reply to #10

Re: Great marine circle method

06/01/2009 8:49 AM

i need to find the direction of shortest path between two points on a sphere mostly separated by a distance <=10km

i have tried the calculator ..but i think its not accurate

are der any other methods to find it???
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Hendrik
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#2

Re: Great marine circle method

05/30/2009 7:16 AM

The great circle route is actually always the shortest distance between two points in a straight line. It only seems like following a curved path because it is represented on an "arbitrary" lat/long grid of the map projection.

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bob c
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#3

Re: Great marine circle method

05/30/2009 9:20 PM

Sure, go ahead. If anyone gives you a hard time, tell them I said it was OK.

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MOBI
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#5

Re: Great marine circle method

05/31/2009 7:24 AM

Here, I thought this was an engineering web site............not a site for "fish heads" (seamen, deck officers, etc)............lets keep the party clean.

Ther ain't too many of the younger brigade that can take readings by sextant........they all rely on GPS's and all of their electronic charts, etc...........better be careful.......that equipment will all soon be made in China............my advice is, learn a little astral navigation it may come in handy...........you could probably learn it from the birds that use it...............this begs a question.

Are birds smarter than "fish heads"?????

The answer should be obvious!!!!!!

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Old Submarine Sailor
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Location: Virginia Beach, VA
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#11
In reply to #5

Re: Great marine circle method

06/01/2009 8:37 AM

MOBI, before I retired a couple of years ago, I used to routinely disable the GPS units we had on board and make the ship's officers navigate celestially and by using dead reckoning. My philosophy was that the first thing we'd lose in a war-time environment would be GPS as it is so easy to jam.

The Junior Officers used to hate it when I would approach them at night and order them to shoot a celestial fix. Then, as their skills developed, it became a contest to see who could be the best celestial navigator and obtain the fix the fastest. I must say with some pride, no one could ever beat me. But, they still tried.

So, not all "fishheads" are dumber than the birds you reference.
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MOBI
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#13
In reply to #11

Re: Great marine circle method

06/01/2009 10:45 AM

Aha! A fishead with brains......very good.......Mind you, you can keep those sludgemarines all to your self........I like to see where I am going, thanks very much. Although I did happen to have the, one of the most upsetting events in my life occur at sea. I was on the HMAS Melbourne (a carrier) when it cut the destroyer HMAS Voyager in half, with the loss of 82 lives. I was out in one of the rescue boats all night...........not a pleasent experience. Anyhow the happy pills keep me going

One of my mates served several years on the Oberon class boats (conventional boats) as Chief of the boat (M/E).

He and several others that I know have since died.........the majority of them submariners on "O" boats.............main cause..... cancer of the stomache or bowel. I perceive that something is not right........I smell a big rat.

Oh! By the way I did not intimate that birds were stupid........ they were created with that navigational sense...........whereas we humans have to learn it.

Cheers my Old Submarine mate

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Anonymous Poster
#6

Re: Great marine circle method

05/31/2009 8:17 AM

Google "Mercator" and you will find several articles that will explain the math.

Mercator was a mathamatician who developed the projection of the earth on flat charts. Also try "Mercator Lines" I think you will find the Info you seak...........
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Andy Germany
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#7

Re: Great marine circle method

05/31/2009 9:26 AM

Maps are flat representation of curved surfaces, the farther you go away from the Equator, the more inaccurate they are. There is now way round this.....

A straight line between two points in the northern hemisphere, will usually make a curving course, too far south. For example, when I first moved to Germany, I used to drive a fairly straight looking route to Calais, which actually added about 100 km to the total journey. When in the MS- DOS days, route finder/calculators became available, I found that driving over Bruxelles was far shorter, in fact the Great Circle route to Calais would actually go over Antwerp!!! But the roads do not lie well for the GCR.....

To illustrate this better, find two places say 1000 miles apart on the map, plot the route on a map. Then go to a Globe with a piece of thread and pull the thread tight over the two places. You will see that theGC route is nowhere near where you thought it should be!!!! If you plot this back onto the flat may, you will see that it curves farther north on the flat map.....

I hope this helps.

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AussieBob
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#14

Re: Great marine circle method

06/03/2009 12:11 AM

Here's a couple of on-line calcs which may be helpful

http://gc.kls2.com/
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Andy Germany (1); AussieBob (1); bob c (1); Hendrik (1); MOBI (2); Old Submarine Sailor (1); rajeshrocks25 (4); TVP45 (2)

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