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Re: ??finding distance of E.Q. from given location??

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I use a program that I wrote for my calculator (based on pretty 
simple spherical-cartesian coordinate transformation).

I assume a perfect sphere with R = 6366 km.  Then I calculate the 3D 
cartesian coordinates of the two points.  The chord distance 
between those points may be calculated as the SRSS of the component 
distances (X1-X2, etc.).  Then I calculate the great circle distance 
based on the chord distance and radius of the earth.

This method is in error in asmuchas the earth is not a perfect 
sphere.  It looks like the web site you indicated can use other 
ellipsoid methods (which would be more accurate).  Based on trials, 
the distance using a spherical assumption is in error by a small 
fraction of 1%, which is close enough for my purposes.

Lat/lon information is reported on all earthquakes.  Lat/lon 
information for a given address can be obtained by using

> From:          "Russel Madere" <rmadere(--nospam--at)>

> I use the Clark 1866 Geoid to calculate the coordinates of each location in
> what ever unit I want and then use Algebra's Pythagerean Theorem to
> calculate the distance.  Not the quickest way by hand, but a PC can handle
> the calculations in seconds.

> ----- Original Message -----
> From: Khosrownia, Ghassem SPK <GKhosrownia(--nospam--at)>
> > In trying to determine distance from epicenter of Hector-Mine and
> Northridge
> > earthquakes from some project sites I found the following link that can
> help
> > in converting the longitude latitude information to distances
> > I have not looked at exactly how
> > this is developed, but it seems the site is developed by a pilot for a
> > pilot. Have you used something like this before? Would you know of a more
> > reliable way to estimate the distances (except scaling off the maps)?

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Michael Valley, P.E., S.E.                       E-mail: mtv(--nospam--at)
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
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