根据 R 中的 GPS 点用方向箭头替换点

Question

我正在根据大量 GPS 点制作运动图表。通常，我只是用一个点来绘制它们，但添加显示鸟移动方向的箭头也很好。但是，我似乎不知道该怎么做。这是我当前地图的代码。正如您所看到的，我尝试使用向下三角形，但它始终指向下方。

我确实有点的方向（称为direction_deg）。我想知道这是否能起到作用。

这是前 300 行数据

dput(head(data_test, n = 300))
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library(ggplot2)

ggplot(data = states) + geom_sf(fill = "grey95", color = "grey70") +
  ##  AF scale
  coord_sf(xlim = c(min_long,max_long),
           ylim = c(min_lat, max_lat),
           expand = F) +
  geom_path(
    data = data,
    aes(x = Longitude, y = Latitude, group = device_id),
    color = "black",
    alpha = 1) +
  geom_point(data = data,
              aes(x = Longitude, y = Latitude, color = device_id),
              shape = 25, 
              size = 4) +
  # annotation_scale(location = 'br') +
  annotation_north_arrow(location = "tl",
                         style = north_arrow_fancy_orienteering)  +
  labs(
    x = "",
    y = "",
    color = "Transmitter",
    title = map_title)+
  theme_light(base_family = "Times New Roman")+
  theme(legend.position = "right", legend.title = element_text(size=30, face="bold"), plot.title = element_text(size=40), text = element_text(size = 30)) +
  scale_color_manual(values = c("#542788", "#E08214")) # change to what you want

这就是我想要的箭头的样子。实际上，我可以取出这些点，然后沿着 geom_path 间隔箭头。什么都是最简单的。

如果您需要任何其他信息，请告诉我！谢谢！！

Answer 1

不幸的是，你的代码除了可重现之外什么都没有（请考虑下一次提供一个reprex，但这里有一个如何使用一些虚假数据解决这个问题的示例。

想法是，不是绘制一个点，而是绘制代表三角形的文本（Unicode

U+25BD

），然后可以旋转该文本：

library(ggplot2)
library(sf)
library(dplyr)

states <- st_as_sf(maps::map("state", fill = TRUE, plot = FALSE))

## generate some fake data

gen_data <- function(x0 = -87.5, y0 = 40, r = 5.5, l = 360, bird = "Bird 1") {
  angles <- seq(0, 360, length.out = l) 
  xx <- x0 + r * cos(angles  / 180 * pi)
  yy <- y0 + r * sin(angles / 180 * pi)
  data.frame(Longitude = xx,
             Latitude = yy,
             device_id = bird,
             direction_deg = angles)
}

path_data <- rbind(gen_data(),
                   gen_data(r = 3, bird = "Bird 2"))
point_data <- path_data %>% 
  filter(row_number() %% 10 == 1)

## now plot the data but use `geom_text` which we can rotate

ggplot(data = states) + 
  geom_sf(fill = "grey95", color = "grey70") +
  coord_sf(xlim = c(-79, -96),
           ylim = c(33, 47),
           expand = TRUE) +
  geom_path(
    data = path_data,
    aes(x = Longitude, y = Latitude, group = device_id),
    color = "black") +
  ## unlike a point we cna rotate text
  geom_text(data = point_data,
            aes(x = Longitude, y = Latitude, color = device_id, 
                angle = direction_deg),
            label = "\U25BC", ## a filled triangle
            size = 4) +
  theme_light() +
  scale_color_manual(values = c("#542788", "#E08214"))