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Here are some functions that I regularly use for geographic data (e.g. binning, filtering, calculation of new positions etc.).

#distance in kilometers between two long/lat positions (from "fossil" package)

earth.dist <- function (long1, lat1, long2, lat2)

{

rad <- pi/180

a1 <- lat1 * rad

a2 <- long1 * rad

b1 <- lat2 * rad

b2 <- long2 * rad

dlon <- b2 - a2

dlat <- b1 - a1

a <- (sin(dlat/2))^2 + cos(a1) * cos(b1) * (sin(dlon/2))^2

c <- 2 * atan2(sqrt(a), sqrt(1 - a))

R <- 6378.145

d <- R * c

return(d)

}

#degree bearing between two long/lat positions (from "fossil" package)

earth.bear <- function (long1, lat1, long2, lat2)

{

rad <- pi/180

a1 <- lat1 * rad

a2 <- long1 * rad

b1 <- lat2 * rad

b2 <- long2 * rad

dlon <- b2 - a2

bear <- atan2(sin(dlon) * cos(b1), cos(a1) * sin(b1) - sin(a1) *

cos(b1) * cos(dlon))

deg <- (bear%%(2 * pi)) * (180/pi)

return(deg)

}

new.lon.lat <-

function (lon, lat, bearing, distance)

{

rad <- pi/180

a1 <- lat * rad

a2 <- lon * rad

tc <- bearing * rad

d <- distance/6378.145

nlat <- asin(sin(a1) * cos(d) + cos(a1) * sin(d) * cos(tc))

dlon <- atan2(sin(tc) * sin(d) * cos(a1), cos(d) - sin(a1) *

sin(nlat))

nlon <- ((a2 + dlon + pi)%%(2 * pi)) - pi

npts <- cbind(nlon/rad, nlat/rad)

return(npts)

}

#tells which lon lat positions are within the defined limits to the west, east, north, and south

lon.lat.filter <-

function (lon_vector, lat_vector, west, east, north, south)

{

if(west>east) {

lon_vector_new=replace(lon_vector, which(lon_vector<0), lon_vector[which(lon_vector<0)]+360)

east_new=east+360

} else {

lon_vector_new=lon_vector

east_new=east

}

hits=which(lon_vector_new < east_new & lon_vector_new > west & lat_vector < north & lat_vector > south)

return(hits)

}

To

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