code_1.R

library(sf)

## Linking to GEOS 3.5.1, GDAL 2.2.1, proj.4 4.9.2, lwgeom 2.3.3 r15473

pnt = read.csv("Points.csv")
pol = read.csv("Natbag2.csv")

pnt = st_as_sf(pnt, coords = c("longitude", "latitude"), crs = 4326)

pol = st_linestring(as.matrix(pol[, c("Longitude", "Latitude")]))
pol = st_cast(pol, "POLYGON")
pol = st_sfc(pol, crs = 4326)
pol = st_sf(pol)

plot(pol)
plot(pnt, add = TRUE)

inside = st_intersects(pnt, pol, sparse = FALSE)

## although coordinates are longitude/latitude, it is assumed that they are planar

inside = inside[, 1]

plot(pol)
plot(pnt[inside, ], col = "red", add = TRUE)
plot(pnt[!inside, ], col = "blue", add = TRUE)