Convert geographical coordinates from degree-minute-second to decimal degrees

If you have latitude and/or longitude data in sexagesimal degrees, in the form degreesº minutes’ seconds” hemisfere (e.g. 41° 34′ 10.956″ N  or  8° 37′ 47.1036″ W, with or without spaces in between), the dms2dec function can convert them to decimal degrees, which are usually required for mapping. This function is not included in a package, but it’s in the “Supplementary Info” of Zanolla et al. (in review), so please cite this paper if you use the function.

dms2dec <- function(dms, separators = c("º", "°", "\'", "\"")) {
  # version 1.0 (25 Sep 3013)
  # dms: a vector (or column) of latitude or longitude in degrees-minutes-seconds-hemisfere, e.g. 41° 34' 10.956" N (with or without spaces)
  # separators: the characters that are separating degrees, minutes and seconds in dms

  dms <- as.character(dms)
  dms <- gsub(pattern = " ", replacement = "", x = dms)
  for (s in separators) dms <- gsub(pattern = s, replacement = "_splitHere_", x = dms)

  splits <- strsplit(dms, split = "_splitHere_")
  n <- length(dms)
  deg <- min <- sec <- hem <- vector("character", n)

  for (i in 1:n) {
    deg[i] <- splits[[i]][1]
    min[i] <- splits[[i]][2]
    sec[i] <- splits[[i]][3]
    hem[i] <- splits[[i]][4]
  }

  dec <- as.numeric(deg) + (as.numeric(min) / 60) + (as.numeric(sec) / 3600)
  sign <- ifelse (hem %in% c("N", "E"), 1, -1)
  dec <- sign * dec
  return(dec)
}  # end dms2dec function 

[presented with Pretty R]

Usage example, from a table called mydata:

LatLonTable

mydata$latitude.decimal <- dms2dec(mydata$Latitude)

mydata$longitude.decimal <- dms2dec(mydata$Longitude)

 

REFERENCES:

Zanolla M., Altamirano M., Carmona R., De La Rosa J., Souza-Egipsy V., Sherwood A., Tsiamis K., Barbosa A.M., Muñoz A.R. & Andreakis N. (in review) Worldwide spread and invasive risk assessment of species with cryptic lineages: the case of the red seaweed genus Asparagopsis (Bonnemaisoniales, Rhodophyta).

Advertisements

2 thoughts on “Convert geographical coordinates from degree-minute-second to decimal degrees

Comment

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s