如何创建多线串sf对象以实现Leaflet地图时间滑块功能

问题根源 #

你之前的代码出错是因为在data.table分组计算时，调用了全局的包含所有月份坐标的mat_list，导致每个月份分组都生成了包含全量数据的多线对象，没有实现按月份拆分的效果。

正确处理逻辑 #

1. 先对每条行程记录，单独生成对应的线段坐标矩阵（注意sf要求坐标顺序是经度在前，纬度在后）
2. 按arrival_month分组，将当月所有线段的坐标矩阵汇总为列表，转换为st_multilinestring对象
3. 生成的sf对象每行对应一个月份的所有路径，可直接传入addTimeslider使用

完整可运行代码 #

# 加载依赖包
library(dplyr)
library(leaflet)
library(leaflet.extras2)
library(sf)
library(data.table)

# 示例数据集
data <- structure(list(arrival_month = structure(c(3L, 3L, 4L, 4L, 4L, 
5L, 5L, 6L, 6L, 6L), .Label = c("January", "February", "March", 
"April", "May", "June", "July", "August", "September", "October", 
"November", "December"), class = c("ordered", "factor")), start_lat = c(33.40693, 
33.64672, 33.57127, 33.42848, 33.54936, 33.53418, 33.60399, 33.49554, 
33.5056, 33.61696), start_long = c(-112.0298, -111.9255, -112.049, 
-112.0998, -112.0912, -112.0911, -111.9273, -111.9687, -112.0563, 
-111.9866), finish_lat...4 = c(33.40687, 33.64776, 33.57125, 
33.42853, 33.54893, 33.53488, 33.60401, 33.49647, 33.5056, 33.61654
), finish_lat...5 = c(-112.0343, -111.9303, -112.0481, -112.0993, 
-112.0912, -112.0911, -111.931, -111.9711, -112.0541, -111.986
)), row.names = c(NA, -10L), class = c("data.table", "data.frame"))

# 按月份生成多线sf对象
sf_month <- data[, 
  # 逐行生成单条行程的线段坐标矩阵
  .(line = list(matrix(
    c(start_long, finish_lat...5, start_lat, finish_lat...4),
    nrow = 2, 
    dimnames = list(c("start", "end"), c("lon", "lat"))
  ))),
  by = .(arrival_month, seq_len(nrow(data)))
][, 
  # 按月份分组，将当月所有线段转为多线对象
  .(geometry = st_sfc(st_multilinestring(line))),
  by = arrival_month
] |> st_as_sf(crs = 4326) # 设定WGS84坐标系

# 测试时间滑块功能
leaflet() |>
  addTiles() |>
  addTimeslider(
    data = sf_month,
    options = timesliderOptions(
      timeAttribute = "arrival_month",
      showControls = TRUE
    )
  )

处理后的sf_month对象每行仅包含对应月份的所有行程路径，完全符合addTimeslider的调用要求，滑动时间滑块即可切换不同月份的路径展示。

内容的提问来源于stack exchange，提问作者Biased_Observer