问如何向sf对象添加点？
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Stack Overflow用户

提问于 2022-09-26 14:42:15

回答 1查看 124关注 0票数 1

我有一个存储点数据的sf对象。但是，我很难理解如何在这个对象中添加点。

我知道如何在单独的对象中创建两点：

# Create sfg objects with coordinates of Los Angeles and Amsterdam
la_sfg <- st_point(c(-118.2615805, 34.1168926))
amsterdam_sfg <- st_point(c(4.8979755, 52.3745403))

我知道如何将这两个物体组合成一个几何集合：

# Create sfc object with multiple sfg objects
points_sfc <- st_sfc(la_sfg, amsterdam_sfg, crs = 4326)
points_sfc

我还知道如何使用dataframe向这些点添加属性：

# Create a data frame of attributes for the two points
data <- data.frame(name = c("Los Angeles", "Amsterdam"),
                   language = c("English", "Dutch"),
   
                weather = c("sunny", "rainy/cold"))

# Make sf object from separate data frame and sfc objects
city_profiles <- st_sf(data, geometry = points_sfc)

现在，假设我有另一个点坐标与以下信息：

name = Toronto
language = English
Coordinates =   c(-79.450717,43.691589)
weather = hot

我很难弄清楚如何创建一个sfg对象，然后将它添加到我先前存在的特性集合中。例如，直觉上我觉得我会做这样的事情：

# Create sfg object
toronto <- st_point(name = "toronto", language = "English",weather = "cold", geometry=c(-79.450717,43.691589))

然后使用rbind将此特性添加到city_profiles中。但是，这不是正确的语法，只返回错误。

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回答 1

Stack Overflow用户

回答已采纳

发布于 2022-09-26 18:17:56

正如SymbolixAU所说，您必须从所有点开始执行所有sf步骤，然后对结果进行rbind。或者先绑定它，然后使用同一个data.frame中的所有点执行所有的data.frame步骤。例如：

library(tidyverse)
library(sf)
library(rnaturalearth)

world <- rnaturalearth::ne_countries(scale = "small",
                                     returnclass = "sf") 

la_ams <- data.frame(name = c("Los Angeles", "Amsterdam"), 
                     language = c("English", "Dutch"),
                     weather = c("sunny", "rainy/cold"), 
                     lon = c(-118.2615805, 4.8979755), 
                     lat = c(34.1168926, 52.3745403))

la_ams <- sf::st_as_sf(la_ams, 
                       coords = c("lon", "lat"),
                       crs = 4269) 

ggplot() +
  geom_sf(data = world,
          mapping = aes(geometry = geometry),
          fill = "white") +
  geom_sf(data = la_ams,
          aes(geometry = geometry),
          size = 3,
          color = "red") +
  theme_bw()

再加一点：

toronto <- data.frame(name = c("toronto"), 
                     language = c("English"),
                     weather = c("cold"), 
                     lon = c(-79.450717), 
                     lat = c(43.691589))

toronto <- sf::st_as_sf(toronto, 
                       coords = c("lon", "lat"),
                       crs = 4269) 

cities <- rbind(la_ams, toronto)

ggplot() +
  geom_sf(data = world,
          mapping = aes(geometry = geometry),
          fill = "white") +
  geom_sf(data = cities,
          aes(geometry = geometry),
          size = 3,
          color = "red") +
  theme_bw()