# R functions for Earth geographic coordinate calculations

May 29, 2011
By

Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

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 southlon.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)} `

R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Tags: , , , ,