"R GIS相交线和多边形（大数据）"

Question

GIS and R question:

I need to intersect many lines with many polygons .

Ideally I would like to do this in R.

Where one line crosses a polygon boundary, I would like that line to be split (making two features / lines).

I would then like to attribute the new (often smaller) lines with the attributes of the polygon that they are now within.

If the lines lie outside a polygon, I would expect the new attributes attached from the polygon to the lines would be NULL or NA or empty.

I am happy to load the data as either shapefiles or geopackages .

What is the best tool to do this with in R?

(I'm happy to use packages such as Raster , rgeos and SF etc. However, ideally, if we can avoid calling QGIS or other software unless it is very stable that would be great. I don't have a licence for Arc)

Many thanks indeed.

Answer 1

Let's collect some online data, a polygon and a couple of lines. We will use osmdata to fetch OSM data for my village.

library(osmdata)
#> Data (c) OpenStreetMap contributors, ODbL 1.0. https://www.openstreetmap.org/copyright
library(sf)
#> Linking to GEOS 3.8.0, GDAL 3.0.4, PROJ 6.3.1; sf_use_s2() is TRUE
library(tidyverse)

Let's find a bounding box and add a bit of space to it

Lbb <- getbb("Lubnów trzebnicki Poland")
addM <- matrix(data = c(-0.01, -0.01, 0.01, 0.01), nrow = 2, ncol = 2)
newBB <- Lbb + addM

Let's fetch highways (lines, multilines) and boundaries (polygons, multipolygons) which we will use in our calculations

highways <- opq (newBB) |> 
  add_osm_feature (key = "highway") |>
  osmdata_sf()

highways <- highways$osm_lines |>
  select(osm_id, name, geometry) |>
  st_as_sf()

boundaries <- opq(newBB) |>
  add_osm_feature (key = "boundary", value = "administrative") |>
  osmdata_sf()

boundariesWsi <- boundaries$osm_multipolygons |>
  filter(boundary == "administrative" & admin_level == 8 & name == "Lubnów")

And let's plot it for visualization

plot(boundariesWsi$geometry, col = "gray90")
plot(highways$geometry, lwd = 0.6, lty = 4, add = TRUE)

We will create a supporting MULTILINESTRING corresponding to village boundaries, which we will use to find only those ways, which croses the boundary

boundariesWsiAsLines <- st_cast(boundariesWsi, "MULTILINESTRING")

Now, let's find those interestingHighways which crosses the village boundaries:

interestingHighways <- highways |> 
  filter(st_intersects(boundariesWsiAsLines$geometry, highways$geometry, sparse = FALSE))

and finally, find IN and OUT parts of those highways:

a<- st_as_sf(st_intersection(interestingHighways$geometry, boundariesWsi$geometry))
b<- st_as_sf(st_difference(interestingHighways$geometry, boundariesWsi$geometry))

plot(a, lwd = 4, col = "darkblue", add = TRUE)
plot(b, lwd = 4, col = "darkgreen", add = TRUE)

Instead of one multipolygon, you can have a list of multipolygons. To assign the attributes to ways, you can use dplyr::mutate() .

^{Created on 2022-01-31 by the reprex package (v2.0.1)}