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

• To: seaint(--nospam--at)seaint.org
• Subject: Re: ??finding distance of E.Q. from given location??
• From: "Michael Valley" <mtv(--nospam--at)skilling.com>
• Date: Wed, 12 Jan 2000 13:37:07 -0700
• Comments: Authenticated sender is <mtv(--nospam--at)mail.skilling.com>
• Priority: normal
```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
www.mapblast.com.

*********

> 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)spk.usace.army.mil>
> > 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
> > http://www.best.com/~williams/gccalc.htm. 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.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201

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