How to clip a polygon shapefile by another polygon shapefile in R? - r

Question

I have two polygons shapefiles and I'd like to clip one by the other. I search on google but I could find only clipping by a bounding box or clipping points by polygons, and that's not what I need.
I also find something in other programming languague, except in R (http://rosettacode.org/wiki/Sutherland-Hodgman_polygon_clipping#Python).
Could you help me?
Thanks
Tiago

Answer 1

Although, the question is very old, providing a good answer might help anyone in the future landing on this page.
I think what you're trying to do is straight forward. To illustrate, lets assume i'm interested in eastern coastline of Saudi Arabia (SA) and i have a shape file that has the east and west coast of SA [ and another shapefile of the Gulf (prominent waterbody on the east coast of SA). We need the SF package to crop the two shape files
Load the SF package
library(sf)
Then load both shapefiles
ksa <- st_read("cropping_shape_file/ksa/saudi_arabia_coastline.shp")
gulf <- st_read("cropping_shape_file/gulf/ihoPolygon.shp")%>%
st_transform(st_crs(ksa)) # The st_transform added to this file ensure that both files have same CRS ssstem otherwise it will be impossible to crop.
you can also check if their CRS is same
st_crs(ksa)==st_crs(gulf)
The sf_read outputs shapefile information into three fields but we're interested in just the geometry
you can
cropped<-st_crop( ksa$geometry, gulf$geometry)
plot(cropped)
You should have an image like
i'm providng the two shape files here https://mega.nz/file/NnxHXajI#KOK_86gwVQGfjNs7X2HOAtvG2NOkIwcU5EhzQU5X6tg, note that a shape file has four component that needs to be kept together(.shp, .prj, .shx, .dbf )

Answer 2

Another way for clipping is to make an selection like "polygontoclip"["templatepolygon", ], found this for points (http://robinlovelace.net/r/2014/07/29/clipping-with-r.html), but also works with polygons.

Answer 3

This doesn't answer your question, but since you mention clipping by bounding box, so this post comes up in search strings:
From r-bloggers: Clipping by a bounding box
setwd("../")
library(rgdal)
zones <- readOGR("data", "london_sport")
make a bounding box:
b <- bbox(zones)
b[1, ] <- (b[1, ] - mean(b[1, ])) * 0.5 + mean(b[1, ])
b[2, ] <- (b[2, ] - mean(b[2, ])) * 0.5 + mean(b[2, ])
b <- bbox(t(b))
plot(zones, xlim = b[1, ], ylim = b[2, ])
Using a custom function:
library(raster)
library(rgeos)
## rgeos version: 0.3-5, (SVN revision 447)
## GEOS runtime version: 3.4.2-CAPI-1.8.2 r3921
## Polygon checking: TRUE
gClip <- function(shp, bb){
if(class(bb) == "matrix") b_poly <- as(extent(as.vector(t(bb))), "SpatialPolygons")
else b_poly <- as(extent(bb), "SpatialPolygons")
gIntersection(shp, b_poly, byid = T)
}
zones_clipped <- gClip(zones, b)
## Warning: spgeom1 and spgeom2 have different proj4 strings
plot(zones_clipped)
Note that due to the if statements in gClip’s body, it can handle almost any spatial data input, and still work.
westminster <- zones[grep("West", zones$name),]
zones_clipped_w <- gClip(zones, westminster)
## Warning: spgeom1 and spgeom2 have different proj4 strings
plot(zones_clipped_w); plot(westminster, col = "red", add = T)

Answer 4

Clip a shapefile by another shapefile
library(raster)
# library(rgdal) # if require
# library(rgeos) # if require
luxembourg <- shapefile(system.file("external/lux.shp", package="raster")) ### load a shape from raster package
plot(luxembourg)
another_shape <- as(extent(6, 6.4, 49.75, 50), 'SpatialPolygons') ### draw a simple shape / load your own
plot(another_shape, add=T, border="red", lwd=3)
luxembourg_clip <- crop(luxembourg, another_shape) ### crop (SpatialPolygon) luxembourg with another_shape
plot(luxembourg_clip, add=T, col=4) ### plot on
plot(luxembourg_clip, add=F, col=3) ### just plot
See some images: Map and Clip
Source: https://rdrr.io/cran/raster/man/crop.html