Plotting lines on map - gcIntermediate

问题

My code works well to produce a map and lines from point A to point B, however for countries in the far eastern hemisphere, the line attempts to cross the shortest path (e.g. east from Australia) and breaks to create a straight line across the plot. Any suggestions? I shortened the code and included it all below to play with.

There was mention (in the link in the code) of using greatCircle, but I could not get this to work.

Thanks!

adds <- c("Argentina",
          "Australia",
          "Germany",
          "Japan",
          "Korea")

# people are coming 'from' all those spots 'to' heidelberg
add0 <- "Salt Lake City, UT"

# get lat / lon
from <- geocode(adds)
to <- geocode(add0)

from

# see: http://flowingdata.com/2011/05/11/how-to-map-connections-with-great-circles/
library(maps)
library(geosphere)


# will need to adjust these limits...
xlim <- c(-170, 200)
ylim <- c(-50, 95)

quartz(file = "UCC.pdf",
       type = "pdf",
       height = 5, width = 9)

#print the map itself
map("world",
    fill=TRUE, 
    xlim=xlim, 
    ylim=ylim,
    # projection = "mercator",
    # orientation=c(90,-111, 0),
    col = grey(0.50),
    bg = grey(0.08), 
    lwd=0.05)

# following gets the 2D projection of a line moving between two points on a sphere
for (i in 1:nrow(from)) {
  inter <- gcIntermediate(c(from[i, "lon"], 
                            from[i, "lat"]), 
                          c(to[1, "lon"], 
                            to[1, "lat"]), 
                          n=500, addStartEnd = T)

  # and plot lines
  lines(inter, 
        col = grey(0.90), 
        lwd = 1)
}

dev.off()

回答1:

Figured out the answer. The breakAtDateLine needs to be set at true. This separates the list and the below code accounts for this by drawing each section of the line separately. Shout-out to DA for the assistance with this.

for (i in 1:nrow(from)) {
  inter <- gcIntermediate(c(from[i, "lon"], 
                            from[i, "lat"]), 
                          c(to[1, "lon"], 
                            to[1, "lat"]), 
                          n=100, addStartEnd=TRUE, breakAtDateLine = T)

if (is.list(inter)) {
  inter1 <- inter[[1]] 
  inter2 <- inter[[2]]
  lines(inter1,
        col = grey(0.90),
        lwd = .75)
  lines(inter2,
        col = grey(0.90),
        lwd = .75)
} else {
  # and plot lines
  lines(inter,
        col = grey(0.90),
        lwd = .75)

}}

dev.off()

来源：https://stackoverflow.com/questions/25881626/plotting-lines-on-map-gcintermediate

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