function to interactively select and extract features from an `SpatialPolygons` or `SpatialPoints` object

extract_spatial.R

extract_spatial<-function(in_spatial,over_poly=NULL,plot_result=FALSE){
  plot(in_spatial)
  message("Select at least 3 points to define the extent")
  coords<-locator() %>% 
    data.frame()
  poly<-rbind(coords,coords[1,]) %>% 
    Polygon() %>% list() %>% 
    Polygons(ID=1) %>% list() %>% 
    SpatialPolygons(proj4string=CRS(proj4string(in_spatial)))
  idx<-over(poly,in_spatial,returnList=TRUE) %>% unlist()
  if(plot_result){
    plot(in_spatial[idx,])
    plot(poly,add=T)
  }
  return(in_spatial[idx,])
}