Ajout d'une barre d'échelle à ggplot carte

Question

J'ai produit cette carte dans ggplot2:

library(maptools); library(ggplot2) 
data(wrld_simpl) 
world <- fortify(wrld_simpl) 
worldUk <- subset(world, id=="GBR") 
ggplot() + 
geom_path(aes(long, lat, group=group), data=worldUk, color="black", fill=NA) + 
    coord_equal() 

l'aide de Photoshop, j'ai ajouté une barre d'échelle sur la carte. Comment puis-je ajouter une barre d'échelle similaire en utilisant ggplot2? Ce message ajoute une barre d'échelle, mais la barre ne fait pas référence à la distance: scale bar and north arrow on map-ggplot2

Answer 1

Il existe une bibliothèque appelée ggsn, qui vous permet de personnaliser la barre d'échelle et la flèche nord.

ggplot() + 
    geom_path(aes(long, lat, group=group), data=worldUk, color="black", fill=NA) + 
    coord_equal() + 
    ggsn::scalebar(worldUk, dist = 100, st.size=3, height=0.01, dd2km = TRUE, model = 'WGS84') 

Answer 2

Je suggérerais annoter(), ce qui vous permettrait de dessiner des segments de bonne longueur dans la zone de traçage. Vous pourriez alors ajouter le texte ci-dessus/ci-dessous comme une étiquette.

Answer 3

J'ai trouvé cette réponse sur http://editerna.free.fr/wp/?p=76 et je l'ai trouvé simple et a fonctionné parfaitement, donc je dois le partager!

Il est simple, d'abord coller le code ci-dessous dans votre console (pas besoin pour le montage)

library(maps) 
library(maptools) 
library(ggplot2) 
library(grid) 
#Then, we need a function to get the scale bar coordinates: 

# 
# Result # 
#--------# 
# Return a list whose elements are : 
# - rectangle : a data.frame containing the coordinates to draw the first rectangle ; 
# - rectangle2 : a data.frame containing the coordinates to draw the second rectangle ; 
# - legend : a data.frame containing the coordinates of the legend texts, and the texts as well. 
# 
# Arguments : # 
#-------------# 
# lon, lat : longitude and latitude of the bottom left point of the first rectangle to draw ; 
# distanceLon : length of each rectangle ; 
# distanceLat : width of each rectangle ; 
# distanceLegend : distance between rectangles and legend texts ; 
# dist.units : units of distance "km" (kilometers) (default), "nm" (nautical miles), "mi" (statute miles). createScaleBar <- 
function(lon,lat,distanceLon,distanceLat,distanceLegend, dist.units = 
"km"){ 
    # First rectangle 
    bottomRight <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon, dist.units = dist.units, model = "WGS84") 

    topLeft <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLat, dist.units = dist.units, model = "WGS84") 
    rectangle <- cbind(lon=c(lon, lon, bottomRight[1,"long"], bottomRight[1,"long"], lon), 
    lat = c(lat, topLeft[1,"lat"], topLeft[1,"lat"],lat, lat)) 
    rectangle <- data.frame(rectangle, stringsAsFactors = FALSE) 

    # Second rectangle t right of the first rectangle 
    bottomRight2 <- gcDestination(lon = lon, lat = lat, bearing = 90, dist = distanceLon*2, dist.units = dist.units, model = "WGS84") 
    rectangle2 <- cbind(lon = c(bottomRight[1,"long"], bottomRight[1,"long"], bottomRight2[1,"long"], bottomRight2[1,"long"], 
bottomRight[1,"long"]), 
    lat=c(lat, topLeft[1,"lat"], topLeft[1,"lat"], lat, lat)) 
    rectangle2 <- data.frame(rectangle2, stringsAsFactors = FALSE) 

    # Now let's deal with the text 
    onTop <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distanceLegend, dist.units = dist.units, model = "WGS84") 
    onTop2 <- onTop3 <- onTop 
    onTop2[1,"long"] <- bottomRight[1,"long"] 
    onTop3[1,"long"] <- bottomRight2[1,"long"] 

    legend <- rbind(onTop, onTop2, onTop3) 
    legend <- data.frame(cbind(legend, text = c(0, distanceLon, distanceLon*2)), stringsAsFactors = FALSE, row.names = NULL) 
    return(list(rectangle = rectangle, rectangle2 = rectangle2, legend = legend)) } We also need a function to obtain the coordinates of the North arrow: 

# 
# Result # 
#--------# 
# Returns a list containing : 
# - res : coordinates to draw an arrow ; 
# - coordinates of the middle of the arrow (where the "N" will be plotted). 
# 
# Arguments : # 
#-------------# 
# scaleBar : result of createScaleBar() ; 
# length : desired length of the arrow ; 
# distance : distance between legend rectangles and the bottom of the arrow ; 
# dist.units : units of distance "km" (kilometers) (default), "nm" (nautical miles), "mi" (statute miles). createOrientationArrow <- 
function(scaleBar, length, distance = 1, dist.units = "km"){ 
    lon <- scaleBar$rectangle2[1,1] 
    lat <- scaleBar$rectangle2[1,2] 

    # Bottom point of the arrow 
    begPoint <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = distance, dist.units = dist.units, model = "WGS84") 
    lon <- begPoint[1,"long"] 
    lat <- begPoint[1,"lat"] 

    # Let us create the endpoint 
    onTop <- gcDestination(lon = lon, lat = lat, bearing = 0, dist = length, dist.units = dist.units, model = "WGS84") 

    leftArrow <- gcDestination(lon = onTop[1,"long"], lat = onTop[1,"lat"], bearing = 225, dist = length/5, dist.units = 
dist.units, model = "WGS84") 

    rightArrow <- gcDestination(lon = onTop[1,"long"], lat = onTop[1,"lat"], bearing = 135, dist = length/5, dist.units = 
dist.units, model = "WGS84") 

    res <- rbind(
      cbind(x = lon, y = lat, xend = onTop[1,"long"], yend = onTop[1,"lat"]), 
      cbind(x = leftArrow[1,"long"], y = leftArrow[1,"lat"], xend = onTop[1,"long"], yend = onTop[1,"lat"]), 
      cbind(x = rightArrow[1,"long"], y = rightArrow[1,"lat"], xend = onTop[1,"long"], yend = onTop[1,"lat"])) 

    res <- as.data.frame(res, stringsAsFactors = FALSE) 

    # Coordinates from which "N" will be plotted 
    coordsN <- cbind(x = lon, y = (lat + onTop[1,"lat"])/2) 

    return(list(res = res, coordsN = coordsN)) } The last function enables the user to draw the elements: 

# 
# Result # 
#--------# 
# This function enables to draw a scale bar on a ggplot object, and optionally an orientation arrow # 
# Arguments : # 
#-------------# 
# lon, lat : longitude and latitude of the bottom left point of the first rectangle to draw ; 
# distanceLon : length of each rectangle ; 
# distanceLat : width of each rectangle ; 
# distanceLegend : distance between rectangles and legend texts ; 
# dist.units : units of distance "km" (kilometers) (by default), "nm" (nautical miles), "mi" (statute miles) ; 
# rec.fill, rec2.fill : filling colour of the rectangles (default to white, and black, resp.); 
# rec.colour, rec2.colour : colour of the rectangles (default to black for both); 
# legend.colour : legend colour (default to black); 
# legend.size : legend size (default to 3); 
# orientation : (boolean) if TRUE (default), adds an orientation arrow to the plot ; 
# arrow.length : length of the arrow (default to 500 km) ; 
# arrow.distance : distance between the scale bar and the bottom of the arrow (default to 300 km) ; 
# arrow.North.size : size of the "N" letter (default to 6). scaleBar <- function(lon, lat, distanceLon, distanceLat, distanceLegend, 
dist.unit = "km", rec.fill = "white", rec.colour = "black", rec2.fill 
= "black", rec2.colour = "black", legend.colour = "black", legend.size = 3, orientation = TRUE, arrow.length = 500, arrow.distance = 300, arrow.North.size = 6){ 
    laScaleBar <- createScaleBar(lon = lon, lat = lat, distanceLon = distanceLon, distanceLat = distanceLat, distanceLegend = 
distanceLegend, dist.unit = dist.unit) 
    # First rectangle 
    rectangle1 <- geom_polygon(data = laScaleBar$rectangle, aes(x = lon, y = lat), fill = rec.fill, colour = rec.colour) 

    # Second rectangle 
    rectangle2 <- geom_polygon(data = laScaleBar$rectangle2, aes(x = lon, y = lat), fill = rec2.fill, colour = rec2.colour) 

    # Legend 
    scaleBarLegend <- annotate("text", label = paste(laScaleBar$legend[,"text"], dist.unit, sep=""), x = 
laScaleBar$legend[,"long"], y = laScaleBar$legend[,"lat"], size = 
legend.size, colour = legend.colour) 

    res <- list(rectangle1, rectangle2, scaleBarLegend) 

    if(orientation){# Add an arrow pointing North 
     coordsArrow <- createOrientationArrow(scaleBar = laScaleBar, length = arrow.length, distance = arrow.distance, dist.unit = 
dist.unit) 
     arrow <- list(geom_segment(data = coordsArrow$res, aes(x = x, y = y, xend = xend, yend = yend)), annotate("text", label = "N", x = 
coordsArrow$coordsN[1,"x"], y = coordsArrow$coordsN[1,"y"], size = 
arrow.North.size, colour = "black")) 
     res <- c(res, arrow) 
    } 
    return(res) } 

Maintenant, pour tracer sur une carte!

Créez d'abord votre carte ggplot, et ajoutez la barre d'échelle comme une couche supplémentaire, en utilisant le signe «+»:

your_ggplot_object -> your_ggplot_object + scaleBar(lon = -130, lat = 26, distanceLon = 500, 
distanceLat = 100, distanceLegend = 200, dist.unit = "km") 

Sur l'exemple ci-dessus, j'appelle la «SCALEBAR fonction», et je précise certaines valeurs pour les arguments. Par exemple, lon = -130, lat = 26 signifie que je veux que le point en bas à gauche du rectangle soit à (-130,26). Vous devez définir les autres valeurs de chaque argument en fonction de ce que vous voulez (il y a une description de chaque argument dans l'en-tête de la fonction).