Distance Between Two Points by Lat/Lon

[onestepcsy37]

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??

[skipmac]

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

[boasun]

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.

[boatman61]

I find a simple chart and dividers quite effective for this... its called basic navigation...
Don't leave home without it...

[Wotname]

Originally Posted by boatman61

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....

[Adelie]

Originally Posted by onestepcsy37

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.

[Adelie]

Originally Posted by boatman61

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.

[Hud3]

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.

[Kijit]

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

Maritime Safety Information

[btrayfors]

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

[Lodesman]

Originally Posted by onestepcsy37

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.

[boatman61]

Originally Posted by Adelie

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

[Adelie]

Originally Posted by boatman61

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

Originally Posted by boatman61

... 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.

[HappySeagull]

Originally Posted by onestepcsy37

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

[onestepcsy37]

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....