How to do an intersection as in st_intersection?

[vronizor]

Hi,

Many thanks for the great package. I was wondering if geometry operations were possible in geos. In particular, I wanted to do an intersection of two collection of features of different length and get a result like in st_intersection. I've been looking around the reference but haven't found a function that does the same. Am I not looking properly or this something not support by geos?

Thanks

[paleolimbot]

You didn't miss anything, it's not obvious! The geos package doesn't do data frame things, but it does provide you the tools to implement it (and maybe it should 🤷 ?).

Here's an example...the totally non-obvious function you're looking for is geos_inner_join_keys().

library(geos)

nc <- sf::read_sf(system.file("shape/nc.shp", package = "sf"))
nc <- tibble::tibble(name = nc$NAME, geom_nc = as_geos_geometry(nc$geometry))

line <- as_geos_geometry("LINESTRING (-85 36, -75 36)")
wk::wk_crs(line) <- wk::wk_crs(nc$geom_nc)
line_df <- tibble::tibble(x = "foofy", geom_line = line)

keys <- geos_inner_join_keys(line_df$geom_line, nc$geom_nc, predicate = "intersects")

intersected <- vctrs::vec_cbind(
  line_df[keys$x, , drop = FALSE],
  nc[keys$y, , drop = FALSE]
)
intersected$geom <- geos_intersection(intersected$geom_line, intersected$geom_nc)
intersected$geom_line <- NULL
intersected$geom_nc <- NULL

plot(nc$geom_nc)
plot(line_df$geom_line, col = "purple", add = T)
plot(intersected$geom, col = "red", add = T)

^{Created on 2024-12-05 with reprex v2.1.1}