[R] converting text coordinates to decimal degrees

[Barry Rowlingson]

Mikkel Grum wrote:
> I receive GPS readings in a text string such as
> "0121.6723S 03643.6893E" and need the coordinates as
> decimal degrees in two separate variables: "-1.361205"
> and "36.728155".  How do I do this in R?

  you'd use some string processing functions, like strsplit, nchar, 
maybe grep and regexp, to build a function like this:

convertCoord <- function(coordString){
   bits <- strsplit(coordString," ")
   lat <- bits[[1]][1]
   lon <- bits[[1]][2]

   mdCon <- function(mdstring){
     d <- as.numeric(substr(mdstring,1,2))
     m <- as.numeric(substr(mdstring,3,99))/60
     return(d+m)
   }

   latD <- mdCon(substr(lat,1,nchar(lat)-1))
   latSign <- ifelse(substr(lat,nchar(lat),nchar(lat))=="N",1,-1)
   lonD <- mdCon(substr(lon,1,nchar(lon)-1))
   lonSign <- ifelse(substr(lon,nchar(lon),nchar(lon))=="E",1,-1)

   c(lonD*lonSign, latD*latSign)

}

  - this works for the single test case you've given us:

 > convertCoord("0121.6723S 03643.6893E")
[1] 13.728155 -1.361205

  - but lots of assumptions are coded into my function. Any deviation 
from that precise format will break it!

  Anyway, that should give you an idea.

Baz