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Re: Nautical Miles to Lat/Lon Degrees [message #17101 is a reply to message #17042]

Sat, 11 September 1999 00:00

Charlie Snedaker
Messages: 1
Registered: September 1999

Junior Member

David,

A nautical mile is, by definition, 1/60 th of a degree of latitude (I
can only give you a reference to Webster's unabridged dictionary as most
of my technical references are at work). The only problem comes when
converting from nautical miles to degrees of longitude since that will
vary according to the latitude. The relations then are

deg_latitude = 1/60 * nm_distance_lat
deg_longitude = (1/60) *nm_distance_long / COS(latitude*!DTOR)

The longitude relationshop has a singularity at +/- 90 degrees since at
the North or South poles an arbitrarily small change in position can
cause a large change in longitude. I would think trapping that condition
and setting the conversion to 180 degrees would be better than letting
it blow up.

Of course, if the distance of interest does not lie along a parallel of
latitude or a meridian of longitude then you have to decompose the
distance into a 'latitudinal' distance and 'longitudinal' distance
before applying the above formulas. Lets say the distance of interest
makes an angle theta with respect to a parallel of latitude. Then just
decompose the distance via

nm_distance_lat = nm_distance * SIN(theta * !DTOR)
nm_distance_long = nm_distance * COS(theta * !DTOR) .

Charlie

David Fanning wrote:

> Hi Folks,
>
> Does anyone know off-hand the formula for converting nautical
> miles to degrees of latitude and longitude for a given
> latitude and longitude? Pointers to appropriate reference
> materials is also appreciated.
>
> Thanks,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting
> Phone: 970-221-0438 E-Mail: davidf@dfanning.com
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Nautical Miles to Lat/Lon Degrees By: davidf on Thu, 09 September 1999 00:00
		Re: Nautical Miles to Lat/Lon Degrees By: Charlie Snedaker on Sat, 11 September 1999 00:00
		Re: Nautical Miles to Lat/Lon Degrees By: Struan Gray on Fri, 10 September 1999 00:00

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