Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 16-04-2011, 22:18   #1
Registered User

Join Date: May 2008
Location: daytona beach florida
Boat: csy 37
Posts: 2,844
Images: 1
Distance Between Two Points by Lat/Lon

seems to me there is a way of calculating distances between two points if their lat/lon is known. or maybe a table to look up. anyone know about this??
__________________

__________________
onestepcsy37 is offline   Reply With Quote
Old 16-04-2011, 22:32   #2
Senior Cruiser
 
skipmac's Avatar

Cruisers Forum Supporter

Join Date: Oct 2007
Location: 29° 49.16’ N 82° 25.82’ W
Boat: Pearson 422
Posts: 12,379
Re: distance between two points by lat/lon

Don't know about a table but the formula requires spherical trigonometry unless there's a short cut I don't know about.
__________________

__________________
The water is always bluer on the other side of the ocean.
skipmac is offline   Reply With Quote
Old 16-04-2011, 22:46   #3
Registered User

Join Date: Nov 2010
Location: Lafayette, Louisiana
Boat: Ketch, Hardin 45
Posts: 440
Images: 6
Re: distance between two points by lat/lon

You can use either Plain sailing or meridian sailing to determine the course and distance between two points. And if you have Transverse tables you can use those also.
I use both plain and meridian sailing. I use a good Sci. caculator to speed the process of doing the math.

And if you are going from one side of an Ocean to the other side you may want to do great circle sailings.
__________________
boasun is offline   Reply With Quote
Old 16-04-2011, 22:59   #4
Freelance Delivery Skipper..
 
boatman61's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2010
Location: UK/Portugal
Posts: 20,207
Images: 2
Send a message via Skype™ to boatman61
pirate Re: distance between two points by lat/lon

I find a simple chart and dividers quite effective for this... its called basic navigation...
Don't leave home without it...
boatman61 is offline   Reply With Quote
Old 16-04-2011, 23:03   #5
Certifiable Refitter/Senior Wannbe
 
Wotname's Avatar

Cruisers Forum Supporter

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: Van DeStat Super Dogger 31'
Posts: 7,331
Re: distance between two points by lat/lon

Quote:
Originally Posted by boatman61 View Post
I find a simple chart and dividers quite effective for this... its called basic navigation...
Don't leave home without it...
Don't you bang them into the GPS and it spits out the distance for you, heck, it evens tells you how to get there - no need for any darn navigation...
Don't leave home without it....
__________________
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
Wotname is offline   Reply With Quote
Old 17-04-2011, 00:24   #6
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,620
Re: distance between two points by lat/lon

Quote:
Originally Posted by onestepcsy37 View Post
seems to me there is a way of calculating distances between two points if their lat/lon is known. or maybe a table to look up. anyone know about this??
dist = 60 x arc-cos[(sinLATi x sinLATf) + (cosLATi x cosLATf) x cos(LONi - LONf)]

West and South Lat and Lon are negative.

From 'Long Distance Cruising' by Bobby Schenk, pg 230.

Or you can look up the distances between ports in NGA Pub #151 downloadable at NGA Publications - Distances Between Ports.
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 17-04-2011, 00:27   #7
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,620
Re: distance between two points by lat/lon

Quote:
Originally Posted by boatman61 View Post
I find a simple chart and dividers quite effective for this... its called basic navigation...
Don't leave home without it...
You're on a roll tonight Boatman, first you pick on Rattleshirt because he's thinking about getting a wooden boat for offshore, now you are picking on Onestep because he wants to know some math.

Dividers and chart only work over short distances, say 100-200nm before projection errors start to become noticable. At several thousand miles the projection errors become pretty significant.
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 17-04-2011, 04:47   #8
CF Adviser
Moderator Emeritus
 
Hud3's Avatar

Cruisers Forum Supporter

Join Date: Sep 2007
Location: Virginia
Boat: Island Packet 380, now sold
Posts: 8,929
Images: 49
Re: Distance Between Two Points by Lat/Lon

I like the idea of knowing the math, Adelie. One could program that formula into an Excel spreadsheet. Also, doing a Google search on "great circle distance calculator" produces a wealth of free online calculators, e.g. MarineWaypoints.com - Great Circle Distance Calculator Your comment about the chart and dividers is correct, of course. No competent navigator would use that technique for anything but coastal short hops.
__________________
Hud
Hud3 is offline   Reply With Quote
Old 17-04-2011, 05:03   #9
Registered User
 
Kijit's Avatar

Join Date: Jun 2010
Location: Virginia
Boat: Wauquiez Centurion 41
Posts: 53
Send a message via Skype™ to Kijit
Re: Distance Between Two Points by Lat/Lon

Go to the NGA site....all kinds of nautical calculators:

Maritime Safety Information
__________________
Gerhard
S/V KIJIT
Wauquiez Centurion 41
Kijit is offline   Reply With Quote
Old 17-04-2011, 06:39   #10
Senior Cruiser

Cruisers Forum Supporter

Join Date: Jul 2006
Location: Chesapeake Region and Maine
Boat: 42' Bob Perry sloop
Posts: 4,038
Images: 4
Re: Distance Between Two Points by Lat/Lon

Google "Mercator Sailing". You'll find lots of online calculators to solve the problem of distance and course.

If the distance is very long, another calculation is useful: Great Circle Distance. This, e.g., is the way radio waves travel and ships and airplanes navigate across oceans to save fuel.

Bill
__________________
btrayfors is offline   Reply With Quote
Old 17-04-2011, 07:00   #11
Senior Cruiser

Cruisers Forum Supporter

Join Date: Nov 2005
Location: Out there doin' it
Boat: 47' Olympic Adventure
Posts: 2,634
Re: Distance Between Two Points by Lat/Lon

Quote:
Originally Posted by onestepcsy37 View Post
seems to me there is a way of calculating distances between two points if their lat/lon is known. or maybe a table to look up. anyone know about this??
Adelie gave you the answer to Great Circle distance in post #6. For a rhumb line, the distance is the difference in Latitude x secant of the course.
__________________
Lodesman is offline   Reply With Quote
Old 17-04-2011, 07:25   #12
Freelance Delivery Skipper..
 
boatman61's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2010
Location: UK/Portugal
Posts: 20,207
Images: 2
Send a message via Skype™ to boatman61
pirate Re: distance between two points by lat/lon

Quote:
Originally Posted by Adelie View Post
You're on a roll tonight Boatman, first you pick on Rattleshirt because he's thinking about getting a wooden boat for offshore, now you are picking on Onestep because he wants to know some math.

Dividers and chart only work over short distances, say 100-200nm before projection errors start to become noticable. At several thousand miles the projection errors become pretty significant.
Not picking on Rattleshirt... if you look at the thread I gave him a composite wooden boat recommendation... its just the thought of someone crossing the Atlantic in an Optimist made me giggle...
And as for the distance question... thats how I do a rough measure of distance... its quicker than punching the info into my H/H GPS...
But then over distances of several thousand miles accuracy of the kind you appear to require is fairly meaningless to me as the varying conditions will increase/decrease the actual miles covered...
But each to their own toy...
I'm happy in my inaccurate world... it works just fine for me
boatman61 is offline   Reply With Quote
Old 17-04-2011, 14:30   #13
Moderator
 
Adelie's Avatar

Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 4,620
Re: distance between two points by lat/lon

Quote:
Originally Posted by boatman61 View Post
Not picking on Rattleshirt... if you look at the thread I gave him a composite wooden boat recommendation... its just the thought of someone crossing the Atlantic in an Optimist made me giggle...
And as for the distance question... thats how I do a rough measure of distance... its quicker than punching the info into my H/H GPS...
But then over distances of several thousand miles accuracy of the kind you appear to require is fairly meaningless to me as the varying conditions will increase/decrease the actual miles covered...
But each to their own toy...
I'm happy in my inaccurate world... it works just fine for me
I can see how the image of sailing the Atlantic in an Optimist would be absurdly funny. And, although the elements are in the thread, I don't see anything that would make that image automatically pop right out. Without context or explaination in your post it really appeared that you were poking fun of him for his dream or me for saying that wood construction generally requires more maintenance.

As for this thread chart and dividers are the obvious way to do a rough calc. Given the sarcasm of your answer

Quote:
Originally Posted by boatman61 View Post
... its called basic navigation...
Don't leave home without it...
it seemed you were belittling him/her for not knowing that one could do the estimate that way, or that they didn't know how to do basic navigation or for not knowing what an appropriate level of accuracy was or all of the above.
__________________
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
SailboatData
Adelie is online now   Reply With Quote
Old 17-04-2011, 15:53   #14
Registered User
 
HappySeagull's Avatar

Join Date: Dec 2010
Location: B.C.,Canada
Boat: 29'
Posts: 2,395
Re: Distance Between Two Points by Lat/Lon

Quote:
Originally Posted by onestepcsy37 View Post
seems to me there is a way of calculating distances between two points if their lat/lon is known. or maybe a table to look up. anyone know about this??
http://www.usps.org/eddept/n/files/Navtra3.zip

this works for GtCircle distance.Also solves the nav triangle...Other cool tools too....at
USPS Educational Department - Offshore Navigation Committee Tools
__________________
HappySeagull is offline   Reply With Quote
Old 17-04-2011, 19:55   #15
Registered User

Join Date: May 2008
Location: daytona beach florida
Boat: csy 37
Posts: 2,844
Images: 1
Re: Distance Between Two Points by Lat/Lon

thanks happy seagull!

sometimes it's fun (but mostly it's not) to wade through the funny and/or well meaning replies to questions, but it's good to find someone who actually knows the answer and provides it in a no nonsense fashion.

i downloaded navtra3.zip and it works perfectly. it definitely merits an icon on my desktop. and yes, i know i can measure distances with dividers (been doing that since the 70's) but it's always nice to have an alternative....
__________________

__________________
onestepcsy37 is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Lat / Lon Grids with C Map 93 r.fairman OpenCPN 4 10-11-2010 15:32
Connectors and NMEA Logger for Depth and Lat / Long Data Skylark Navigation 1 17-08-2010 08:34
Need Lat / Long of Sunken Atoll Duckhead Pacific & South China Sea 7 11-12-2009 11:25
High Lat. Optical Illusions Tim Gosnell Polar Regions 24 12-02-2006 23:45
Distance from Lat/Lon GordMay The Library 0 30-06-2005 19:27



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:41.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.