通过连接点（lon-lat）在R中绘制的Google地图上查找位置的区域

Question

I am trying to calculate area of a marked location with points and lines using ggmap and ggplot2 libraries. I am not finding any example of how to calculate areas by connecting points of longitudes and latitudes in R.

My code for the points and lines of the location for which I am working to find area is below:

library(ggmap)
library(ggplot2)

coordinates <- read.csv("U://30-Power & Water//25 Renewables//R plots//plant location plot//lat_lon.csv", header=T)

coordinates <- data.frame(coordinates) 

map <- get_map(location = c(mean(coordinates[1:13,3]), mean(coordinates[1:13,2])), zoom = 13, maptype = "satellite", source = "google")

Sweihan <- ggmap(map)+
  geom_point(data = coordinates, aes(x = coordinates[,3], y = coordinates[,2]))+
  geom_path(data = coordinates, aes(x = coordinates[,3], y = coordinates[,2]))
+ geom_polygon(data = coordinates, aes(x = coordinates[1:13,3], y = coordinates[1:13,2])) 

Sweihan

My data looks like this :

     Point Latitute..N. Longitude..
1     P1     24.53450    55.41547
2     P2     24.52929    55.41913
3     P3     24.52929    55.43241
4     P4     24.54342    55.46566
5     P5     24.55113    55.46241
6     P6     24.55545    55.47364
7     P7     24.56041    55.47109
8     P8     24.55841    55.46529
9     P9     24.55867    55.46521
10   P10     24.54863    55.43838
11   P11     24.54712    55.43917
12   P12     24.54085    55.42715
13   P13     24.54043    55.42712
14    P1     24.53450    55.41547

please help me finding approach for calculating area that I can use within my code so that when I plot points of lat and lon on the map, I get the exact area that these points cover.

Any type of your help will be appreciated!

Answer 1

Here is a more generic approach to find the area of a polygon described by a set of coordinates. This uses the active simplefeatures standard for spatial data provided by the package sf . The steps go as follows:

1. Read in the points to a table with read_table2()
2. Select only the coordinate columns and convert to a matrix with as.matrix()
3. Wrap inside a list with list() . This is necessary to convert the coordinates into a geometry object.
4. Use st_polygon to turn the points into a polygon
5. Use st_sfc and st_set_crs to give the package an understanding that the polygon coordinates are in a latitude/longitude system (4326 is a code that corresponds to the extremely common WGS84 standard for coordinate data)
6. Use st_area to calculate the area of the polygon.

The code for this is a straightforward pipe:

library(sf)

tbl <- readr::read_table2(
  "Point Latitude Longitude
  P1     24.53450    55.41547
  P2     24.52929    55.41913
  P3     24.52929    55.43241
  P4     24.54342    55.46566
  P5     24.55113    55.46241
  P6     24.55545    55.47364
  P7     24.56041    55.47109
  P8     24.55841    55.46529
  P9     24.55867    55.46521
  P10     24.54863    55.43838
  P11     24.54712    55.43917
  P12     24.54085    55.42715
  P13     24.54043    55.42712
  P1     24.53450    55.41547"
) 

tbl[, c(3,2)] %>%
  as.matrix() %>%
  list() %>%
  st_polygon() %>%
  st_sfc() %>% 
  st_set_crs(4326) %>% 
  st_area()
7919415 m^2

Answer 2

For a matrix of lon/lat coordinates

p <- rbind(c(-180,-20), c(-140,55), c(10, 0), c(-140,-60), c(-180,-20))
library(geosphere)
areaPolygon(p)

# with your data "d"
# areaPolygon(as.matrix(d[,3:2]))

Or for a SpatialPolygonsDataFrame

library(raster)
p <- shapefile(system.file("external/lux.shp", package="raster"))
a <- area(p)