如何绘制角度在 0-360 度之间的线条

Question

I want to plot a time-angle series in xy coordinates. when the difference between two neighbors is less than 180, they will be lined directly. Otherwise, one will be lined to 360 and another will be lined to 0 with the same time, it means the path crossed the 0/360 point. What I known is to calculate the two interpolating points first, and plot two segments, is there some smart direct way to do that?

library(ggplot2)
data<-data.frame(time=c(1,2,3,4),angle=c(200,100,320,20))
#ggplot()+geom_line(data,aes(time,angle))
#three lines codes is expected,but now it is->
ymax=360
ymin=0
ythd=(ymax-ymin)/2 #180
j=1 #left end point number
n=nrow(data)# rignt end point number
aid=data[1,] #aids line from end point to border
gg=ggplot()
for(i in 1:(n-1)){
  delta=data[i+1,2]-data[i,2]
  #divide groups
  if(abs(delta)>ythd){
    gg=gg+geom_line(data=data[j:i,],aes(time,angle))
    j=i+1
    fst=data[i,2]
    stp=data[j,1]-data[i,1]
    aid[1,]=data[i,]
    #interpolating points
    if(delta>0){
      rto=fst/(360-(delta))
      aid[2:3,1]=data[i,1]+rto*stp
      aid[2,2]=ymin
      aid[3,2]=ymax
    }else{
      rto=(360-fst)/(360+delta)
      aid[2:3,1]=data[i,1]+rto*stp
      aid[2,2]=ymax
      aid[3,2]=ymin
    }
    aid[4,]=data[j,]
    #aids line
    gg=gg+geom_line(data=aid[1:2,],aes(time,angle))   
    gg=gg+geom_line(data=aid[3:4,],aes(time,angle))   
  }

}
#the last group
gg=gg+geom_line(data=data[j:n,], aes(time,angle))
gg

Expected output:

Answer 1

This was a fun exercise. Here's what I came up with. I only tested on this one dataset so it may need some tweaking.

library(tidyverse)
data<-data.frame(t1=c(1,2,3,4),a1=c(200,100,300,20))

data <- data %>%
  arrange(t1) %>%
  mutate(t2 = c(data$t1[-1], 0)) %>%
  mutate(a2 = c(data$a1[-1], 0)) %>%
  mutate(grp = 0)


get_split <- function(t1, t2, a1, a2) {
  # TEST: t1=1;t2=2;a1=10;a2=355
  if((a2 - a1) > 180) {
    return(a1/(a1 + 360 - a2)*(t2 - t1) + t1)
  } else {
    return(NA)
  }
}

data <- rbind(
  data[,c('t1', 'a1', 'grp')],
  data.frame(t1 = mapply(get_split, data$t1, data$t2, data$a1, data$a2),
             a1 = 0,
             grp = 0),
  data.frame(t1 = mapply(get_split, data$t1, data$t2, data$a1, data$a2),
             a1 = 360,
             grp = 1)
)

data <- data[!is.na(data$t1),] %>%
  arrange(t1)

data$grp <- cumsum(data$grp)

ggplot(data) +
  geom_line(aes(x = t1, y = a1, group = grp))