Determining a coordinate given another coordinate, a great circle distance, and an angle

Harry, I think you are after something like the function below (I did not
test it much). Robert
# based on code at http://www.movable-type.co.uk/scripts/latlong.html
# ? 2002-2009 Chris Veness
# license: LPGL; without any warranty express or implied
# R version by R Hijmans
# calculate destination point given start point, initial bearing (deg) and
distance (km)
# ? see http://williams.best.vwh.net/avform.htm#LL
destPoint <- function(lon, lat, bearing, d, dms=FALSE, R=6378137) {
# bearing in degrees
# d in meters
# R=earth's mean radius in m
RadDeg <- pi / 180

lat1 = lat * RadDeg
lon1 = lon * RadDeg
brng = bearing * RadDeg
lat2 <- asin( sin(lat1) * cos(d/R) + cos(lat1) * sin(d/R) * cos(brng) )
lon2 <- lon1 + atan2(sin(brng) * sin(d/R) * cos(lat1), cos(d/R) - sin(lat1)
* sin(lat2))
lon2 <- (lon2 + pi) %% ( 2 * pi) - pi; # normalise to -180...+180
if (is.nan(lat2) | is.nan(lon2)) return(NULL)
return ( (cbind(lon2, lat2)) / RadDeg )
}
destPoint(35, 25, 30, 100000)





On Tue, Oct 6, 2009 at 10:22 AM, Harry Kim <harryk at cal.berkeley.edu> wrote:

Dear R-sig-geoers,

? ? ?I am stuck with a problem and i was hoping if you could help me.
Suppose i am given a coordinate in lat/long (say 25 lat 35 long) and a
great circle distance (say 10km). Also assume that i am given an angle
with respect to latitude (an angle from the x-axis say 30 degrees).
What would be the best way to determine a coordinate 10kms away from
25 lat 35 long with a given angle (30 degrees)?

? ? I think in euclidean space, I can use tangent of the given angle
and combine with the Pythagorean theorem to find the target
coordinate.

Thank you very much in advance,
Harry