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Subject: Re: query
From: Dan Allen (danallen46@XXX.XXX)
Date: Wed Aug 21 2002 - 13:58:04 EDT
On Wednesday, August 21, 2002, at 10:34 AM, Mitch B Burrill wrote:
> If I am at lat1, long1, and go XXX nm at TC YYY,
> What is the exact formula from spherical trigonometry to get lat2,
> long2 ?
> I have looked everywhere for this, I must be doing something wrong.
Check out http://williams.best.vwh.net/avform.htm
which has this:
Lat/lon given radial and distance
A point {lat,lon} is a distance d out on the tc radial from point 1 if:
lat=asin(sin(lat1)*cos(d)+cos(lat1)*sin(d)*cos(tc))
IF (cos(lat)=0)
lon=lon1 // endpoint a pole
ELSE
lon=mod(lon1-asin(sin(tc)*sin(d)/cos(lat))+pi,2*pi)-pi
ENDIF
This algorithm is limited to distances such that dlon <pi/2, i.e those
that extend around less than one quarter of the circumference of the
earth in longitude. A completely general, but more complicated algorithm
is necessary if greater distances are allowed:
lat =asin(sin(lat1)*cos(d)+cos(lat1)*sin(d)*cos(tc))
dlon=atan2(sin(tc)*sin(d)*cos(lat1),cos(d)-sin(lat1)*sin(lat))
lon=mod( lon1-dlon +pi,2*pi )-pi
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