Converting geo coordinates from degree to decimal

Question

I want to convert my geographic coordinates from degrees to decimals, my data are as follows:

         lat     long
105252 30°25.264 9°01.331
105253 30°39.23         


        

Answer 1

Try using the char2dms function in the sp library. It has other functions that will additionally do decimal conversion.

library("sp")
?char2dms

Answer 2

As Jim Lewis commented before it seems your are using floating point minutes. Then you only concatenate two elements on

dec=c(as.numeric(tmp1[[1]][1]),as.numeric(tmp2[[1]]))

Having degrees, minutes and seconds in the form 43°21'8.02 which as.character() returns "43°21'8.02\"", I updated your function to

convert<-function(coord){
  tmp1=strsplit(coord,"°")
  tmp2=strsplit(tmp1[[1]][2],"'")
  tmp3=strsplit(tmp2[[1]][2],"\"")
  dec=c(as.numeric(tmp1[[1]][1]),as.numeric(tmp2[[1]][1]),as.numeric(tmp3[[1]]))
  c<-abs(dec[1])+dec[2]/60+dec[3]/3600
  c<-ifelse(dec[1]<0,-c,c)
  return(c)
}

adding the alternative for negative coordinates, and works great for me . I still don't get why char2dms function in the sp library didn't work for me.

Thanks

Answer 3

Thanks for answers by @Gord Stephen and @CephBirk. Sure helped me out. I thought I'd just mention that I also found that measurements::conv_unit doesn't deal with "E/W" "N/S" entries, it requires positive/negative degrees. My coordinates comes as character strings "1 1 1W" and needs to first be converted to "-1 1 1".
I thought I'd share my solution for that.

df <- c("1 1 1E", "1 1 1W", "2 2 2N","2 2 2S")  
measurements::conv_unit(df, from = 'deg_min_sec', to = 'dec_deg')
[1] "1.01694444444444" NA                 NA                 NA  
Warning message:
In split(as.numeric(unlist(strsplit(x, " "))) * c(3600, 60, 1),  :
  NAs introduced by coercion

ewns <- ifelse( str_extract(df,"\\(?[EWNS,.]+\\)?") %in% c("E","N"),"+","-")
dms <- str_sub(df,1,str_length(df)-1)
df2 <- paste0(ewns,dms)

df_dec <- measurements::conv_unit(df2, 
                                  from = 'deg_min_sec', 
                                  to = 'dec_deg'))
df_dec
[1] "1.01694444444444"  "-1.01694444444444" "2.03388888888889"  "-2.03388888888889"
as.numeric(df_dec)
[1]  1.016944 -1.016944  2.033889 -2.033889

Answer 4

Have a look at the command degree in the package OSMscale.

Answer 5

A bit of vectorization and matrix manipulation will make your function much simpler:

x <- read.table(text="
       lat     long
105252 30°25.264 9°01.331
105253 30°39.237 8°10.811
105255 31°37.760 8°06.040
105258 31°41.190 8°06.557
105259 31°41.229 8°06.622
105260 31°38.891 8°06.281",
                header=TRUE, stringsAsFactors=FALSE)

x

The function itself makes use of:

• strsplit() with the regex pattern "[°\\.]" - this does the string split in one step
• sapply to loop over the vector

Try this:

convert<-function(x){
  z <- sapply((strsplit(x, "[°\\.]")), as.numeric)
  z[1, ] + z[2, ]/60 + z[3, ]/3600
} 

Try it:

convert(x$long)
[1] 9.108611 8.391944 8.111111 8.254722 8.272778 8.178056

---

Disclaimer: I didn't check your math. Use at your own discretion.

Answer 6

Another less elegant option using substring instead of strsplit. This will only work if all your positions have the same number of digits. For negative co-ordinates just multiply by -1 for the correct decimal degree.

x$LatDD<-(as.numeric(substring(x$lat, 1,2))
+ (as.numeric(substring(x$lat, 4,9))/60))
x$LongDD<-(as.numeric(substring(x$long, 1,1))
       + (as.numeric(substring(x$long, 3,8))/60))