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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation > figuring distance from Lat/lon
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Topic Review (Newest First)
06-10-2004 05:02 PM
ekraemer
figuring distance from Lat/lon

This is a reliable page for Great Circle info.

http://williams.best.vwh.net/avform.htm

Thanks,
Ed
04-14-2004 12:56 PM
c172guy
figuring distance from Lat/lon

I wonder about distances from a chart. Only the latitude is accurate and if it''s a mercador projection a straight line is about 12% longer than a great circle route.
This came up because I didn''t have the correct chart handy and wanted to estimate time in route.
If I am actually on the boat I just enter the destination into the gps and it gives all the navigation data. But what if it dies??? I like to be able to dead reckon. I figure the more stuff I know the better.
04-13-2004 07:00 AM
Sailmc
figuring distance from Lat/lon

Wouldn''t it be easier to just measure it on the chart?
04-13-2004 06:49 AM
c172guy
figuring distance from Lat/lon

Thanks for the formulas. They seem to be the same as my math teacher friend provided. My GPS will calculate distances I just was curious about how to do it with a calculator. Actually my knot meter is not that acurate so that it''s error is probably my greatest source of error.
Thanks
Tom
04-12-2004 05:55 PM
geohan
figuring distance from Lat/lon

c 172guy: My Garmin GPS will compute the Great Circle distance for me after I enter the lat and long for each point. Maybe yours will also. Check the owners manual for instructions.

If you have to do it the hard way, "Dutton" gives the Haversine Formula as:
hav dist = (hav DLo)(cos L1)(cos L2)+ hav(L1-L2)
DLo is the difference in longitude and L1-L2 is the difference in latitudes.
If you don''t have Haversine Tables, substitute
(1-cosX)/2 for hav X
Have Fun, George
04-12-2004 03:51 PM
GordMay
figuring distance from Lat/lon

By definition, 1 minute of longitude at the equator is equal to 1 nautical mile.

For a chart - goto “The Earth according to WGS 84"
http://home.online.no/~sigurdhu/Grid_1deg.htm

Regards,
Gord
04-12-2004 03:13 PM
Fishboat
figuring distance from Lat/lon

How about this?

http://jan.ucc.nau.edu/~cvm/latlongdist.html
04-12-2004 01:56 PM
ccboston
figuring distance from Lat/lon

some discussion here
http://www.movable-type.co.uk/scripts/LatLong.html
04-12-2004 12:26 PM
c172guy
figuring distance from Lat/lon

I checked a couple of books without an answer. My neighbor is a math teacher and showed me a way. But there''s got to be a better way. I just used trigonometry converting minutes into miles and solving for the hypoteneuse using Pythagorum''s theroem. But we all know the earth is a sphere so as the distance increases so does the error. Sort of transforming the lat/lon into vectors with the earths radius and calculating the distance is there a way to calculate the distance between two points using only lat/lon coordinates??? Please forgive the spelling.

 
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