Converting coordinates from degree with unconventional format to decimal degree - r

Question

I am trying to convert my data so that it can be plotting on a map. For example the data looks like:
# A tibble: 2 x 2
Latitud Longitud
<chr> <chr>
1 10º 35' 28.98'' N 3º 41' 33.91'' O
2 10º 35' 12.63'' N 3º 45' 46.22'' O
I am trying to mutate it using the following:
df %>%
mutate(
Latitud = str_replace_all(Latitud, "''", ""),
lat_edit = sp::char2dms(Latitud), "°")
Which returns and error:
Error in if (any(abs(object#deg) > 90)) return("abs(degree) > 90") :
missing value where TRUE/FALSE needed
In addition: Warning message:
In asMethod(object) : NAs introduced by coercion
I would like to plot these two points on a map in ggplot (or another spatial package)
Data:
structure(list(Latitud = c("40º 25' 25.98'' N", "40º 25' 17.63'' N"
), Longitud = c("3º 42' 43.91'' O", "3º 40' 56.22'' O")), class = c("tbl_df",
"tbl", "data.frame"), row.names = c(NA, -2L))

Answer 1

You can use the following custom function (I am assuming N, S, W, E. Not sure what O means in longitude):
angle2dec <- function(angle) {
angle <- as.character(angle)
angle <- ifelse(grepl("S|W", angle), paste0("-", angle), angle)
angle <- trimws(gsub("[^- +.0-9]", "", angle))
x <- do.call(rbind, strsplit(angle, split=' '))
x <- apply(x, 1L, function(y) {
y <- as.numeric(y)
(abs(y[1]) + y[2]/60 + y[3]/3600) * sign(y[1])
})
return(x)
}
Applying on the data:
df1[] <- lapply(df1, angle2dec)
df1
#> Latitud Longitud
#> 1 -40.42388 3.712197
#> 2 40.42156 -3.682283
Plotting:
library(ggplot2)
ggplot(df1, aes(x = Longitud, y = Latitud)) +
geom_point()
Slightly Modified Data to Show for Different Hemispheres:
df1 <- structure(list(Latitud = c("40<U+623C><U+3E61> 25' 25.98'' S",
"40<U+623C><U+3E61> 25' 17.63'' N"),
Longitud = c("3<U+623C><U+3E61> 42' 43.91'' E",
"3<U+623C><U+3E61> 40' 56.22'' W")),
class = c("tbl_df", "tbl", "data.frame"),
row.names = c(NA, -2L))
In reference to Converting geo coordinates from degree to decimal .

Answer 2

I'll preface this by saying I hadn't used char2dms until right now, so there may be intricacies I missed (such as my question above about "O" as a direction). Looking at the docs and examples, you need to give the characters used to demarcate degrees, minutes, and seconds. In your case, these are "º", "'", and "''", respectively. I skipped the step of removing the third of these, because it's necessary to see where the seconds are written. (Update: added a step to replace the regex "O$" (oeste) with "W" (west)). That gets you what's below:
library(dplyr)
library(ggplot2)
library(sp)
dat <- structure(list(Latitud = c("40º 25' 25.98'' N", "40º 25' 17.63'' N"
), Longitud = c("3º 42' 43.91'' O", "3º 40' 56.22'' O")), class = c("tbl_df",
"tbl", "data.frame"), row.names = c(NA, -2L)) %>%
mutate_at(vars(Latitud, Longitud), stringr::str_replace_all, "O$", "W")
char2dms(dat$Latitud, chd = "º", chm = "'", chs = "''")
#> [1] 40d25'25.98"N 40d25'17.63"N
This is a DMS S3 object, not a vector (here's where my knowledge of this ends), so you can't put it directly into the data frame columns. Instead, convert to a numeric vector, and you've got numeric coordinates in your data frame.
dat_numeric <- dat %>%
mutate(lat_edit = as.numeric(char2dms(dat$Latitud, chd = "º", chm = "'", chs = "''")),
lon_edit = as.numeric(char2dms(dat$Longitud, chd = "º", chm = "'", chs = "''")))
dat_numeric
#> # A tibble: 2 x 4
#> Latitud Longitud lat_edit lon_edit
#> <chr> <chr> <dbl> <dbl>
#> 1 40º 25' 25.98'' N 3º 42' 43.91'' W 40.4 -3.71
#> 2 40º 25' 17.63'' N 3º 40' 56.22'' W 40.4 -3.68
Plot like normal numbers:
ggplot(dat_numeric, aes(x = lon_edit, y = lat_edit)) +
geom_point()
Or convert to an sf object and plot with the appropriate aspect ratio, projection, etc.
sf::st_as_sf(dat_numeric, coords = c("lon_edit", "lat_edit")) %>%
ggplot() +
geom_sf()