我有來自不同地理區域收集的不同資料集的點集群。我想在地圖上繪制每個區域的空間范圍，為此我需要每個區域一個多邊形。我可以通過“連接點”找到將點轉換為多邊形的命令，但沒有通過繪制輪廓（幾何方法不是非常重要，因為這僅用于繪圖）。這是一個 reprex，用于生成像我正在使用的那樣的簡化資料框，用于挪威、阿拉斯加和美國大陸的點：
nor_lat <- c(72.117, 71.05, 71.717, 71.167, 71.817, 72.333, 71.25, 70.917,
70.85, 70.933)
nor_lon <- c(33.217, 30.333, 26.3, 22.333, 22.333, 22.333, 18.517, 20.133,
21.333, 19.917)
us_lat <- c(41.283333, 41, 40.95, 40.95, 38.683333, 40.783333, 40.733333,
40.516667, 38.566667, 41.266667)
us_lon <- c(-71.116667, -70.733333, -70.583333, -70.483333, -74.816667,
-70.5, -70.566667, -70.266667, -74.85, -71.366667)
ak_lat <- c(58.015, 57.67167, 57.33833, 56.685, 56.99333, 57.31667, 57.65,
57.99667, 58.32167, 58.33333)
ak_lon <- c(-158.31667, -158.36, -158.41, -159.76, -159.72333, -159.66333,
-159.64167, -159.605, -159.54, -160.72167)
nor_dat <- data.frame(lat=nor_lat, lon=nor_lon)
us_dat <- data.frame(lat=us_lat, lon=us_lon)
ak_dat <- data.frame(lat=ak_lat, lon=ak_lon)
nor_dat$region <- "nor"
us_dat$region <- "us"
ak_dat$region <- "ak"
dat <- rbind(nor_dat, us_dat, ak_dat)
對于 object dat，我想在 each 中的點周圍生成一個簡單的多邊形region，如果可能，使用 sf 。（我不太擔心弄清楚如何迭代區域，但我什至不知道如何圍繞一組點繪制多邊形！）
uj5u.com熱心網友回復：
一種使用sf和dplyr用于“地理計算”和過濾tmap以及tmaptools用于可視化的方法。
請找到以下reprex。
正品
- 將
dataframe“資料”轉換為sf物件
library(sf)
library(dplyr)
library(tmap)
library(tmaptools)
sf_use_s2(TRUE)
dat_sf <- st_as_sf(dat, coords = c("lon", "lat"), crs = 4326)
- 為每個區域中的每組點計算平滑的包絡多邊形
conv_nor <- st_simplify(st_buffer(st_convex_hull(st_union(st_geometry(filter(dat_sf, region == "nor")))), dist = 15000), dTolerance = 5000)
conv_us <- st_simplify(st_buffer(st_convex_hull(st_union(st_geometry(filter(dat_sf, region == "us")))), dist = 15000), dTolerance = 5000)
conv_ak <- st_simplify(st_buffer(st_convex_hull(st_union(st_geometry(filter(dat_sf, region == "ak")))), dist = 15000), dTolerance = 5000)
- 可視化：概述
tm_shape(dat_sf)
tm_dots(size = 0.2, col = "black", shape = 21, alpha = 0.3)
tm_shape(conv_nor)
tm_borders(col = "gray", lwd = 2)
tm_shape(conv_us)
tm_borders(col = "blue", lwd = 2)
tm_shape(conv_ak)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE)
- 可視化：詳細視圖
tm_shape(filter(dat_sf, region == "nor"), bbox = bb(conv_nor, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_nor)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'nor' area",
title.size = 1.5, title.position = c(0.85, "bottom"))
tm_shape(filter(dat_sf, region == "us"), bbox = bb(conv_us, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_us)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'us' area",
title.size = 1.5, title.position = c(0., "top"))
tm_shape(filter(dat_sf, region == "ak"), bbox = bb(conv_ak, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_ak)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'ak' area",
title.size = 1.5, title.position = c(0.75, "top"))
- 帶背景的詳細視圖
最后，如果你想要一些背景關系背景，你可以使用tmap_mode("view")which 呼叫leaflet- 顯然你在海洋環境作業;-)
tmap_mode("view")
#> tmap mode set to interactive viewing
tm_shape(filter(dat_sf, region == "nor"), bbox = bb(conv_nor, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_nor)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'nor' area",
title.size = 1.5, title.position = c(0.85, "bottom"))
tm_shape(filter(dat_sf, region == "us"), bbox = bb(conv_us, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_us)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'us' area",
title.size = 1.5, title.position = c(0., "top"))
tm_shape(filter(dat_sf, region == "ak"), bbox = bb(conv_ak, ext = 1))
tm_dots(size = 0.5, alpha = 0.5)
tm_shape(conv_ak)
tm_borders(col = "gray", lwd = 2)
tm_layout(frame = FALSE, title = "'ak' area",
title.size = 1.5, title.position = c(0.75, "top"))
tmap_mode("plot")
#> tmap mode set to plotting
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