如何在R中的极坐标中添加时间维度？

Question

我试图用ggplot2绘制一只鸟在南极周围的轨迹。 到目前为止，我得到了一个以极坐标投影的地图，我还设法正确绘制了轨迹点，我几乎正确地将它们连接起来......但是当轨道越过国际DATE＆TIME线时 ， ggplot2无法正确链接2在线的两侧各点。所以我正在寻找一种方法来强制ggplot以连续的方式连接点。

这是我的数据集：

Data =>
ID  Date      Time   A1   Lat.    Long.
10 12.9.2008 22:00   1  21.14092 70.98817 
10 12.9.2008 22:20   1  21.13031 70.97592 
10 12.9.2008 22:40   2  21.13522 70.97853 
10 12.9.2008 23:00   1  21.13731 70.97817
10 12.9.2008 23:20   3  21.14197 70.97981
10 12.9.2008 23:40   1  21.14156 70.98158
10 12.9.2008 23:40   1  21.14156 70.98158
10 13.9.2008 00:00   2  21.14150 70.98478
10 13.9.2008 00:20   3  21.14117 70.98803
10 13.9.2008 00:40   1  21.14117 70.98803
10 13.9.2008 01:00   2  21.14117 70.98803

....

ID是鸟的ID。

使用Nick K代码更新

这是我的原始图表，没有使用时间维度和行

south_map <- map_data("world") %>% group_by(group) 
set.seed(123)

track_df2 <- new_df2

long_diff <- diff(new_df2$Long)
long_diff[long_diff < -180] <- long_diff[long_diff < -180] + 360
long_diff[long_diff > 180] <- long_diff[long_diff > 180] - 360
track_df2$Longitude <- cumsum(c(new_df2$Long[1], long_diff))

ggplot(track_df2, aes(x = track_df2$Long, y = track_df2$Lat)) +
geom_polygon(aes(group = a3_id), data = south_map, colour = "grey", fill = "gainsboro") +
geom_point(aes(colour = factor(a3_id)), size = 2)

A1定义了鸟目前正在做什么。

Answer 1

你似乎没有在你的情节中实际使用时间，但问题是经度在-180/180左右。 这可以使用coord_map而不是coord_polar来解决，并确保经度不会回绕。

加载包并生成样本数据

library("ggplot2")
library("dplyr")
south_map <- map_data("world") %>% group_by(group) %>% filter(min(lat) <= -20)

set.seed(123)
track <- data.frame(long = cumsum(c(210,
                                    unlist(lapply(c(1, -1), function(x) {
                                      rnorm(50, x * 4, 4)
                                      })))) %% 360 - 180,
                    lat = cumsum(c(-50, rnorm(100, 0.4, 2))),
                    A1 = sample(1:3, 101, replace = TRUE))

确保坐标不包围：

track_new <- track
long_diff <- diff(track$long)
long_diff[long_diff < -180] <- long_diff[long_diff < -180] + 360
long_diff[long_diff > 180] <- long_diff[long_diff > 180] - 360
track_new$long <- cumsum(c(track$long[1], long_diff))

绘图使用aziequidistant投影。 请注意，这假设北极位于中心，因此纬度被翻转然后用比例校正。

ggplot(track_new, aes(x = long, y = -lat)) +
  geom_polygon(aes(group = group), data = south_map, colour = "grey", fill = "gainsboro") +
  coord_map("azequidistant") +
  geom_point(aes(colour = factor(A1)), size = 2) +
  geom_path(colour = "grey", size = 1) +
  scale_x_continuous(breaks = NULL) +
  scale_y_continuous("latitude", breaks = 25 * 0:3, labels = -25 * 0:3)

最终情节：

只是为了兴趣，我认为制作这个图像的动画会很有趣。 这是执行此操作的代码：

track_new$alpha <- 1
# Setup longitude labels

long_labels <- data.frame(long = 45 * -3:4, lat = -22.5)
long_labels$label <- long_labels$long
long_labels$label[8] <- "\U00B1 180"
long_labels$angle <- long_labels$long + 67.5 + 180 * (long_labels$long >= 45)

# Set up the basic plot
p <- ggplot(track_new, aes(x = long, y = -lat)) +
  geom_polygon(aes(group = group), data = south_map, colour = "grey", fill = "gainsboro") +
  coord_map("azequidistant", ylim = c(20, 90)) +
  geom_point(aes(colour = A1, alpha = alpha), size = 2) +
  geom_path(aes(alpha = alpha), colour = "grey", size = 1) +
  scale_x_continuous(breaks = NULL) +
  scale_y_continuous("latitude", breaks = 22.5 * 0:3, labels = -22.5 * 0:3) +
  scale_alpha_identity(guide = "none") +
  geom_text(aes(label = label, angle = angle),
            data = long_labels, colour = "dark blue", alpha = 0.5, size = 4)

# Produce the animation
p$data$alpha <- 0
for(i in 1:(nrow(track_new) + 10)) {
  p$data$alpha <- pmax(p$data$alpha - 0.1, 0)
  if (i <= nrow(track_new)) {
    p$data$alpha[i] <- 1
  }
  png(file.path("BirdPlots", sprintf("BirdPlot%03d.png", i)), width = 1024, height = 1024, res = 100)
  print(p)
  dev.off()
  if (!(i %% 5)) cat(i, "\n")
}

# This needs ImageMagick in the system path. For non-Windows systems, you
# might be better using system rather than shell
shell(paste("convert", file.path("BirdPlots", "BirdPlot*.png"),
  file.path("BirdPlots", "BirdPlotAnimation.gif")))

这是结果：

编辑修正了ayush代码的版本

track_df2 <- new_df2

long_diff <- diff(new_df2$Longitude)
long_diff[long_diff < -180] <- long_diff[long_diff < -180] + 360
long_diff[long_diff > 180] <- long_diff[long_diff > 180] - 360
track_df2$Longitude <- cumsum(c(new_df2$Longitude[1], long_diff))

track_df2$a3_id <- factor(track_df2$a3_id)

ggplot(track_df2, aes(x = Longitude, y = -Latitude)) +
  coord_map("azequidistant", ylim = c(20, 90)) +
  geom_point(aes(colour = a3_id, alpha = alpha), size = 2) +
  geom_path(aes(alpha = alpha), colour = "grey", size = 1) +
  scale_x_continuous(breaks = NULL) +
  scale_y_continuous(breaks = 22.5 * 0:3, labels = -22.5 * 0:3) +
  scale_alpha_identity(guide = "none")