How to draw circles of defined radius around multiple points and export to kml file

Question

I have a set of points saved with their respective latitude and longitude in a data frame like this:

points = data.frame(point_id = 1:3,
                lat = c("51.7505","51.7502","51.6045"),
                long = c("4.8456","4.8453","4.8012")
                )

My goal is to create circular polygons with the same defined radius (in this case 200m) around each of these points and export them as a KML file. How would I do that?

Answer 1

Use st_buffer with a metric projection (you have to st_transform the crs first).

library(sf)
points <- st_as_sf(points, coords = c("lat", "long"), crs = 4326) %>% 
  st_transform(20539) %>% 
  st_buffer(200)

Then use st_write:

st_write(points , "points.kml", driver = "kml", delete_dsn = TRUE)

Answer 2

points_buffer <- points %>%
        # Transform data.frame in Simple Feature object
        st_as_sf(coords = c('lat', 'long'), dim = "XY") %>% 
        # Determine the coordinate system
        st_set_crs("EPSG:4326") %>%
        # Tranform geographical coordinates to cartesian
        # so we can choose the size of the buffer in meters
        st_transform( crs = 27700)  %>%
        # Calculate buffer
        st_buffer(dist = 200) %>%
        # Return to WGS 84 geographical coordinate system to export in KML
        st_transform( crs = 4326)


# Export results
st_write(points_buffer, "points_buffer.kml", driver = "kml", delete_dsn = TRUE)