使用st_buffer围绕地理点圈出

Question

我想使用sf套餐在都柏林机场周围110海里（海里）绘制一个圆圈。 （稍后我会通过st_intersect与ADS-B的航班位置报告相交。）

我已为NM定义了一个新单元，如下所示：

library(units)
library(tidyverse)
library(sf)
NM <- make_unit("NM")
install_conversion_constant("NM", "km", 1.852)

然后定义都柏林机场坐标：

# DUB/EIDW location, see 
# https://skyvector.com/airport/EIDW/Dublin-Airport
# Coordinates:
#   N53°25.28' / W6°16.20' (Degrees Decimal Minutes (DDM) format)
#   (-6.27, 53.421333) (lon/lat Decimal Degrees (DD))
# Elevation: 242.0 feet (MSL)
dub_lon <- -6.27
dub_lat <- 53.421333
dub_elv <- set_units(242.0, ft)

dub <- st_point( x = c(dub_lon, dub_lat, dub_elv), dim = "XYZ")
dub <- dub %>% st_sfc(crs = 4326)

因此定义了机场周围的圆的半径（以米为单位）：

r110 <- set_units(110, NM) %>% set_units(km)

现在，当我尝试st_buffer时，事情无效：

> r110 <- set_units(110, NM) %>% set_units(km)
Error: cannot convert km into °
In addition: Warning message:
In st_buffer.sfc(dub, dist = r110) :
  st_buffer does not correctly buffer longitude/latitude data, dist needs to be in decimal degrees.

如果我尝试传递一个数值（203.72，这些是km）作为距离，至少我只得到一个警告：

> dub110 <- st_buffer(dub, dist = 203.72)
Warning message:
In st_buffer.sfc(dub, dist = 203.72) :
  st_buffer does not correctly buffer longitude/latitude data, dist needs to be in decimal degrees.

但是绘制它显示的是一个相当大的圈子

library(mapview)
mapview(dub110)

我应该在dist中输入st_buffer的单位是多少？ 我阅读了文档，但没有真正知道该怎么做......

任何提示/帮助真的很感激！

Answer 1

Thanks to Phil and Jul the complete solution to the initial question is as follows:

library(units)
library(tidyverse)
library(sf)
library(mapview)
library(units)

# define nautical miles (as per ICAO notation)
NM <- make_unit("NM")
install_conversion_constant("NM", "km", 1.852)

# DUB/EIDW location, see
# https://skyvector.com/airport/EIDW/Dublin-Airport
# Coordinates:
#   N53°25.28' / W6°16.20' (Degrees Decimal Minutes (DDM) format)
#   (-6.27, 53.421333) (lon/lat Decimal Degrees (DD))
# Elevation: 242.0 feet (MSL)
dub_lon <- -6.27
dub_lat <- 53.421333
dub_elv <- set_units(242.0, ft)
dub <- st_point(x = c(dub_lon, dub_lat, dub_elv), dim = "XYZ")
dub <- dub %>% st_sfc(crs = 4326)

# define radious of interest, i.e. 110 NM
r110 <- set_units(110, NM) %>% set_units(km) %>% set_units(m)

# change to Irish grid, which uses meters
dub <- st_transform(dub, 29902)
dub_buffer <-  st_buffer(dub, r110)

# eventually convert back to WSG84 if needed for other purposes
dub <- st_transform(dub, 4326)
dub_buffer <- st_transform(dub_buffer, 4326)
mapview(dub_buffer)

Answer 2

如果您愿意，这里有一个纯粹的sf答案，但@Jul是完全可以使用的。

设置为您的示例：

library(units)
library(tidyverse)
library(sf)
NM <- make_unit("NM")
install_conversion_constant("NM", "km", 1.852)

# DUB/EIDW location, see 
# https://skyvector.com/airport/EIDW/Dublin-Airport
# Coordinates:
#   N53°25.28' / W6°16.20' (Degrees Decimal Minutes (DDM) format)
#   (-6.27, 53.421333) (lon/lat Decimal Degrees (DD))
# Elevation: 242.0 feet (MSL)
dub_lon <- -6.27
dub_lat <- 53.421333
dub_elv <- set_units(242.0, ft)

dub <- st_point(x = c(dub_lon, dub_lat, dub_elv), dim = "XYZ")
dub <- dub %>% st_sfc(crs = 4326)

然后将坐标转换为Irish Grid：

dub = st_transform(dub, 29902)

围绕此点以米为单位创建缓冲区：

dub_buffer = st_buffer(dub, 110000)

绘制结果：

plot(dub_buffer)
plot(dub, add = TRUE)

Answer 3

如Phil所述，您需要将坐标转换为米/'距离'投影，而不是基于度数的投影。

我不熟悉sf，但sp ...

library(sp) 
dub_transformed <- spTransform(dub,CRS("+init=epsg:29902")) 

...在运行buffer命令之前应该足够了。 然后，您可能希望将缓冲的对象转换回epsg：4326以进行绘图/附加处理。例如

dub110 <- spTransform(dub110,CRS("+init=epsg:4326"))