我能够绘制地图和标题的特定点:
library(maps)
map("state")
text(-80.83,35.19,"Charlotte",cex=.6)
我还可以绘制一个以该点为中心的圆圈:
symbols(-80.83,35.19,circles=2, add=TRUE)
但是,我想控制圆圈的大小。特别是,我想在data.frame,矩阵或列表中包含的多个位置周围绘制一个半径为100英里的圆。
答案 0 :(得分:14)
Gary的命题很适合平面地图,但不能应用于“地图”包生成的地图,因为它不会处理用于绘制地图的投影。严格应用,它会导致绘制一个椭圆(见下文),因为圆半径的单位是度,但不是公里或英里。但纬度和经度的度数不对应于相同的物理距离。要绘制一个圆周点或一个接近圆的东西,其半径是以英里或公里为单位的恒定距离,您需要计算有关投影的校正坐标。根据{{3}}的Chris Veness解释你的功能并使其适应,你的功能变为:
library(maps)
library(mapdata)#For the worldHires database
library(mapproj)#For the mapproject function
plotElipse <- function(x, y, r) {#Gary's function ;-)
angles <- seq(0,2*pi,length.out=360)
lines(r*cos(angles)+x,r*sin(angles)+y)
}
plotCircle <- function(LonDec, LatDec, Km) {#Corrected function
#LatDec = latitude in decimal degrees of the center of the circle
#LonDec = longitude in decimal degrees
#Km = radius of the circle in kilometers
ER <- 6371 #Mean Earth radius in kilometers. Change this to 3959 and you will have your function working in miles.
AngDeg <- seq(1:360) #angles in degrees
Lat1Rad <- LatDec*(pi/180)#Latitude of the center of the circle in radians
Lon1Rad <- LonDec*(pi/180)#Longitude of the center of the circle in radians
AngRad <- AngDeg*(pi/180)#angles in radians
Lat2Rad <-asin(sin(Lat1Rad)*cos(Km/ER)+cos(Lat1Rad)*sin(Km/ER)*cos(AngRad)) #Latitude of each point of the circle rearding to angle in radians
Lon2Rad <- Lon1Rad+atan2(sin(AngRad)*sin(Km/ER)*cos(Lat1Rad),cos(Km/ER)-sin(Lat1Rad)*sin(Lat2Rad))#Longitude of each point of the circle rearding to angle in radians
Lat2Deg <- Lat2Rad*(180/pi)#Latitude of each point of the circle rearding to angle in degrees (conversion of radians to degrees deg = rad*(180/pi) )
Lon2Deg <- Lon2Rad*(180/pi)#Longitude of each point of the circle rearding to angle in degrees (conversion of radians to degrees deg = rad*(180/pi) )
polygon(Lon2Deg,Lat2Deg,lty=2)
}
map("worldHires", region="belgium")#draw a map of Belgium (yes i am Belgian ;-)
bruxelles <- mapproject(4.330,50.830)#coordinates of Bruxelles
points(bruxelles,pch=20,col='blue',cex=2)#draw a blue dot for Bruxelles
plotCircle(4.330,50.830,50)#Plot a dashed circle of 50 km arround Bruxelles
plotElipse(4.330,50.830,0.5)#Tries to plot a plain circle of 50 km arround Bruxelles, but drawn an ellipse
(对不起,我的“声望”不允许我发布图片;-)。编辑:添加了您的图片。
我希望这会有所帮助。 格雷
答案 1 :(得分:1)
您可以编写一个功能来自定义圆圈的外观。例如:
plotCircle <- function(x, y, r) {
angles <- seq(0,2*pi,length.out=360)
lines(r*cos(angles)+x,r*sin(angles)+y)
}
然后,如果您在数据框中有一组坐标:
coords <- data.frame(x = c(-1,0,1), y = c(-1, 0.5, 1))
您可以从一些初始情节(地图或空图等)开始
plot(1,type='n',xlim=c(-2,2),ylim=c(-2,2))
然后在坐标列表上调用绘图功能:
apply(coords,1,function(df) plotCircle(df[1],df[2],.3))