Revisiting the “Format latitude and longitude axis labels in ggplot”

问题

the question/problem is very similar to the original question: change the decimal degrees to degrees minutes seconds in the ggplot axis labels.

I'm following these steps:

library(ggplot2)
library(ggmap)

#get my map
city<- get_map(location = c(lon= -54.847, lat= -22.25),
                maptype = "satellite",zoom = 11,color="bw")

map<-ggmap(city,extent="normal")+
  xlab("Longitude")+ ylab("Latitude")
map

In addition, I'm trying what @Jaap wrote:

scale_x_longitude <- function(xmin=-180, xmax=180, step=1, ...) {
  xbreaks <- seq(xmin,xmax,step)
  xlabels <- unlist(lapply(xbreaks, function(x) ifelse(x < 0, parse(text=paste0(x,"^o", "*W")), ifelse(x > 0, parse(text=paste0(x,"^o", "*E")),x))))
  return(scale_x_continuous("Longitude", breaks = xbreaks, labels = xlabels, expand = c(0, 0), ...))
}
scale_y_latitude <- function(ymin=-90, ymax=90, step=0.5, ...) {
  ybreaks <- seq(ymin,ymax,step)
  ylabels <- unlist(lapply(ybreaks, function(x) ifelse(x < 0, parse(text=paste0(x,"^o", "*S")), ifelse(x > 0, parse(text=paste0(x,"^o", "*N")),x))))
  return(scale_y_continuous("Latitude", breaks = ybreaks, labels = ylabels, expand = c(0, 0), ...))
} 

So:

map+
  scale_x_longitude(-55.0,-54.7,4)+
  scale_y_latitude(-22.4,-22.1,4)

In the second map only two coordinates are draw and in the wrong format. I need these corrdinates written as follow:

55ºW, 54ºW 54',54ºW 48', 54ºW 42'; 22ºS 24', 22ºS 18', 22ºS 12', 22ºS 06'

Can anyone help me?

Update (16/08/2017) Here is a update code provided by @Rafael Cunha (Thanks a lot!) Still missing a way to add minutes symbol. However, it is working better than before.

scale_x_longitude <- function(xmin=-180, xmax=180, step=1, ...) {
  xbreaks <- seq(xmin,xmax,step)
  xlabels <- unlist(
    lapply(xbreaks, function(x){
      ifelse(x < 0, parse(text=paste0(paste0(abs(dms(x)$d),"^{o}*"),
                                      paste0(abs(dms(x)$m)), "*W")), 
             ifelse(x > 0, parse(text=paste0(paste0(abs(dms(x)$d),"^{o}*"),
                                             paste0(abs(dms(x)$m)),"*E")),
                    abs(dms(x))))}))
  return(scale_x_continuous("Longitude", breaks = xbreaks, labels = xlabels, expand = c(0, 0), ...))
}

scale_y_latitude <- function(ymin=-90, ymax=90, step=0.5, ...) {
  ybreaks <- seq(ymin,ymax,step)
  ylabels <- unlist(
    lapply(ybreaks, function(x){
      ifelse(x < 0, parse(text=paste0(paste0(abs(dms(x)$d),"^{o}*"),
                                      paste0(abs(dms(x)$m)),"*S"), 
             ifelse(x > 0, parse(text=paste0(paste0(abs(dms(x)$d),"^{o}*"),
                                             paste0(abs(dms(x)$m)),"*N")),
                    abs(dms(x))))}))
  return(scale_y_continuous("Latitude", breaks = ybreaks, labels = ylabels, expand = c(0, 0), ...))
}  

map+
  scale_x_longitude(-55.0,-54.7,.1)+
  scale_y_latitude(-22.4,-22.1,.1)

回答1:

@Thiago Silva Teles,

Building off of the code that @Rafael Cunha provided (Thanks, I will be using this too), the expression function works (for me anyhow) to provide degree, minute, and second labels on the plot axis.

Functions to convert DD to DMS for ggmap axis plotting.

scale_x_longitude <- function(xmin=-180, xmax=180, step=0.002, ...) {
  xbreaks <- seq(xmin,xmax,step)
  xlabels <- unlist(
    lapply(xbreaks, function(x){
      ifelse(x < 0, parse(text=paste0(paste0(abs(dms(x)$d), expression("*{degree}*")),
                                      paste0(abs(dms(x)$m), expression("*{minute}*")),
                                      paste0(abs(dms(x)$s)), expression("*{second}*W"))), 
             ifelse(x > 0, parse(text=paste0(paste0(abs(dms(x)$d), expression("*{degree}*")),
                                             paste0(abs(dms(x)$m), expression("*{minute}*")),
                                             paste0(abs(dms(x)$s)), expression("*{second}*E"))),
                    abs(dms(x))))}))
  return(scale_x_continuous("Longitude", breaks = xbreaks, labels = xlabels, expand = c(0, 0), ...))
}

scale_y_latitude <- function(ymin=-90, ymax=90, step=0.002, ...) {
  ybreaks <- seq(ymin,ymax,step)
  ylabels <- unlist(
    lapply(ybreaks, function(x){
      ifelse(x < 0, parse(text=paste0(paste0(abs(dms(x)$d), expression("*{degree}*")),
                                      paste0(abs(dms(x)$m), expression("*{minute}*")),
                                      paste0(abs(dms(x)$s)), expression("*{second}*S"))), 
             ifelse(x > 0, parse(text=paste0(paste0(abs(dms(x)$d), expression("*{degree}*")),
                                             paste0(abs(dms(x)$m), expression("*{minute}*")),
                                             paste0(abs(dms(x)$s)), expression("*{second}*N"))),
                    abs(dms(x))))}))
  return(scale_y_continuous("Latitude", breaks = ybreaks, labels = ylabels, expand = c(0, 0), ...))
}  

Example map for Stackexchange

library(ggplot2)
library(ggmap)
map <- get_map(location = "Alabama",
               zoom = 8,
               maptype = "toner", source = "stamen",
               color = "bw")
sam_map <- ggmap(map) +
  theme_minimal() + theme(legend.position = "none")

sam_map +
  scale_x_longitude(-89, -85, 0.75) +
  scale_y_latitude(30, 34, 0.75)

I had to tinker with "step" (within function code and call) to have it display correctly and at desired intervals. This could still be improved to omit seconds or minutes at larger scales. I do like that it provides decimal seconds at very small scales. Not much of a programmer/coder, but this does seem to work.

Map of LA (Lower Alabama) with DMS (proper formatting)

回答2:

I use the function dms from GEOmap package to transform decimal degrees into degrees minutes seconds. The only thing that is missing in my code is a way to paste the minutes in the axis labels.

library(ggplot2) library(ggmap) library(GEOmap)

#get my map
city<- get_map(location = c(lon= -54.847, lat= -22.25),
               maptype = "satellite",zoom = 11,color="bw")

map<-ggmap(city,extent="normal")+
  xlab("Longitude")+ ylab("Latitude")

scale_x_longitude <- function(xmin=-180, xmax=180, step=1, ...) {
  xbreaks <- seq(xmin,xmax,step)
  xlabels <- unlist(lapply(xbreaks, function(x) ifelse(x < 0, parse(text=paste0(abs(dms(x)$d),"^o", "*W")), ifelse(x > 0, parse(text=paste0(abs(dms(x)$d),"^o", "*E")),abs(dms(x))))))
  return(scale_x_continuous("Longitude", breaks = xbreaks, labels = xlabels, expand = c(0, 0), ...))
}
scale_y_latitude <- function(ymin=-90, ymax=90, step=0.5, ...) {
  ybreaks <- seq(ymin,ymax,step)
  ylabels <- unlist(lapply(ybreaks, function(x) ifelse(x < 0, parse(text=paste0(abs(dms(x)$d),"^o", "*S")), ifelse(x > 0, parse(text=paste0(abs(dms(x)$d),"^o", "*N")),abs(dms(x))))))
  return(scale_y_continuous("Latitude", breaks = ybreaks, labels = ylabels, expand = c(0, 0), ...))
} 

map+
  scale_x_longitude(-55.0,-54.7,.1)+
  scale_y_latitude(-22.4,-22.1,.1)

来源：https://stackoverflow.com/questions/45698588/revisiting-the-format-latitude-and-longitude-axis-labels-in-ggplot