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06-02-2013, 03:27
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#1
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cruiser
Join Date: Dec 2012
Location: Seattle
Posts: 1,129
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Coordinate Math Question
Is there a recognized way to deduce one position from another?
That it, given a bouy, and the coordinates for it in degrees, minutes and seconds, is it possible to determine mathematically the coordinates for a point 200 yards west of it?
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06-02-2013, 03:41
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#2
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Registered User
Join Date: Dec 2009
Posts: 2,959
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Ya. Too easy. 200 yards is 600 feet. A nautical mile and therefore a minute of longitude is about 6000 feet. So that's 0.1 minute of position west.
What? You are stuck in a cold latitude and not here on the equator where minutes of longitude are not 6000 feet. Multiply by the cosine of your unfortunate latitude.
It's all done for you with the MEASURE tool in OpenCPN.
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06-02-2013, 03:42
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#3
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,242
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Re: Coordinate Math Question
Err.. trick question or am I missing something here?
I don't recall the maths involved to convert distance into degrees longitude but is was simple when I did know it . It is a dependant on the latitude as in sin or cos or tan or something of the lat. times the distance in question (in nm).
So in the given example, the lat will remain the same and the long will be increased/decreased the required seconds.
Now hopefully someone with a better memory will chime in.
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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06-02-2013, 03:44
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#4
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,242
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Re: Coordinate Math Question
Quote:
Originally Posted by daddle
Ya. Too easy. 200 yards is 600 feet. A nautical mile and therefore a minute of longitude is about 6000 feet. So that's 0.1 minute of position west.
What? You are stuck in a cold latitude and not here on the equator where minutes of longitude are not 6000 feet. Multiply by the cosine of your unfortunate latitude.
It's all done for you with the MEASURE tool in OpenCPN.
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Daddle is a minute faster (poor pun intended) and has better memory plus knows his cosines
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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06-02-2013, 03:51
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#5
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Registered User
Join Date: Dec 2009
Posts: 2,959
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Ya folks. Look at the time stamps! 2 minutes to answer that. And on an iPhone keyboard in a bar after many happy hour beers too!
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06-02-2013, 04:13
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#6
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cruiser
Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 5,030
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Re: Coordinate Math Question
without google!!!!!!
Maybe....
New Lat = Old Lat +(cos(course*dist)
New Long= Old long + (sin(course*dist)*90/oldlat
Better hit send quick before someone else gets in, haven't checked that yet ....
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06-02-2013, 05:34
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#7
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Moderator Emeritus
Join Date: Jul 2010
Location: Key West & Sarasota
Boat: Cal 28 "Happy Days"
Posts: 4,210
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Re: Coordinate Math Question
Or for we non-engineer types: Get in dink with GPS, paddle over to point in question, take reading, paddle back!
__________________
Any fool with a big enough checkbook can BUY a boat; it takes a SPECIAL type of fool to build his own! -Capngeo
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06-02-2013, 05:38
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#8
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cruiser
Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 5,030
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Re: Coordinate Math Question
Quote:
Originally Posted by conachair
without google!!!!!!
Maybe....
New Lat = Old Lat +(cos(course*dist)
New Long= Old long + (sin(course*dist)*90/oldlat
Better hit send quick before someone else gets in, haven't checked that yet ....
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should be (course)*distance...
all in decimal degrees , no so sure about the 90/oldlat - anyone actually know this stuff?
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06-02-2013, 05:48
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#9
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Moderator and Certifiable Refitter
Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,242
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Re: Coordinate Math Question
Quote:
Originally Posted by conachair
should be (course)*distance...
all in decimal degrees , no so sure about the 90/oldlat - anyone actually know this stuff?
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Used to
Not now
I blame GPS
Time hasn't been kind to my little used maths brain cell s
Thanks for the memories Jamer Six
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
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06-02-2013, 06:02
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#10
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Registered User
Join Date: Oct 2009
Location: Australia
Boat: CT 54... for our sins!
Posts: 2,083
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Re: Coordinate Math Question
Sheeeeeeeeeeeeesh!
But I do know how to varnish...
Vic
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06-02-2013, 06:02
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#11
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Registered User
Join Date: Mar 2008
Location: Huron, Ohio
Boat: Albin Coronado 35(1972)
Posts: 640
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Re: Coordinate Math Question
GO TO .........
The NGS Geodetic Tool Kit
theN download .........
Inverse/Forward/Invers3D/Forwrd3D
this is a program for inversing lats & longs
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06-02-2013, 09:36
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#12
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Moderator Emeritus
Join Date: May 2008
Location: Fort Lauderdale, FL
Boat: 48 Wauquiez Pilot Saloon
Posts: 5,975
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Re: Coordinate Math Question
Quote:
Originally Posted by capngeo
Or for we non-engineer types: Get in dink with GPS, paddle over to point in question, take reading, paddle back!
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cap'n... You forgot "grab drink" then dink.... You couldn't possibly pull this task off without refreshment....
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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06-02-2013, 16:47
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#13
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cruiser
Join Date: Dec 2012
Location: Seattle
Posts: 1,129
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Re: Coordinate Math Question
Oh, dear...
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06-02-2013, 19:05
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#14
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Registered User
Join Date: Nov 2010
Posts: 406
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It has been a while...but the longitude of a known east west distance would depend on the latitude you are at. That is why you always get distance by measuring latitude when plotting with dividers...tell what I am missing...be gentle...long day
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