Showcase of creation and plotting of great circle lines

great_circle_lines.R

# this code showcases creation and plotting of great circle lines

# first install missing packages
# thanks to Pratik Patil for the package installation code ( http://stackoverflow.com/a/29622385 )
# Specify the list of required packages to be installed and load    
Required_Packages = c("leaflet", "sp", "geosphere", "scales")

Install_And_Load <- function(Required_Packages) {
        Remaining_Packages <- Required_Packages[!(Required_Packages %in% installed.packages()[,"Package"])]
        
        if(length(Remaining_Packages)) 
        {
                install.packages(Remaining_Packages)
        }
        for(package_name in Required_Packages)
        {
                library(package_name, character.only = T, quietly = F)
        }
}

# Call the Function
Install_And_Load(Required_Packages)


# sample code for drawing great circle lines

draw_great_circle_lines <- function() {
        
        n = 20 # set number of random points - adjust to your liking, but be careful - too many points may slow down the rendering of the lines
        
        # create a data table with random points - all points are approximately in Russia
        x <- data.frame( oLat = runif(n, min = 50, max = 69), # origin lat
                         oLon = runif(n, min = 30, max = 170), # origin lon
                         dLat = runif(n, min = 50, max = 69), # destination lat
                         dLon = runif(n, min = 30, max = 170), # destination lon
                         value = runif(n, min = 100, max = 1000)) # random migration values
        
        # create origin and destination points
        oX <- x # copy data frame for origins
        coordinates(oX) = ~ oLon + oLat # create spatial object
        proj4string(oX) = CRS("+init=epsg:4326") # set coordinate system to WGS84
        dX <- x # copy data frame for destinations
        coordinates(dX) = ~ dLon + dLat # create spatial object
        proj4string(dX) = CRS("+init=epsg:4326") # set coordinate system to WGS84
        
        
        xPaths <- gcIntermediate(oX, dX, n = 50, addStartEnd = T, sp = T) # create great circle paths
        xPaths <- SpatialLinesDataFrame(sl = xPaths, data = x["value"]) # attach the random migration values from original table
        
        xPaths@data$value_scaled <- rescale( log(xPaths@data$value), to = c(1, 2)) # normalise the values to appropriate line widths
        xPaths@data$value_opacity <- rescale( log(xPaths@data$value), to = c(0.05, 0.25)) # normalise the values to use for opacity
        
        # plot object with leaflet
        m = leaflet() %>%
                addTiles() %>%  # Add default OpenStreetMap map tiles
                addPolylines(data = xPaths,
                             color = "red",
                             weight = xPaths@data$value_scaled,
                             opacity = xPaths@data$value_opacity,
                             popup = xPaths@data$value)
        m
        
}