Check which mesh triangles are inside a polygon

Wrapper for the sf::st_contains() (previously sp::over()) method to find triangle centroids or vertices inside sf or sp polygon objects

Usage

fm_contains(x, y, ...)

# S3 method for class 'Spatial'
fm_contains(x, y, ...)

# S3 method for class 'sf'
fm_contains(x, y, ...)

# S3 method for class 'sfc'
fm_contains(x, y, ..., type = c("centroid", "vertex"))

Arguments

x: geometry (typically an sf or sp::SpatialPolygons object) for the queries
y: an fm_mesh_2d() object
...: Passed on to other methods
type: the query type; either 'centroid' (default, for triangle centroids), or 'vertex' (for mesh vertices)

Value

List of vectors of triangle indices (when type is 'centroid') or vertex indices (when type is 'vertex'). The list has one entry per row of the sf object. Use unlist(fm_contains(...)) if the combined union is needed.

Author

Haakon Bakka, bakka@r-inla.org, and Finn Lindgren Finn.Lindgren@gmail.com

Examples

# Create a polygon and a mesh
obj <- sf::st_sfc(
  sf::st_polygon(
    list(rbind(
      c(0, 0),
      c(50, 0),
      c(50, 50),
      c(0, 50),
      c(0, 0)
    ))
  ),
  crs = fm_crs("longlat_globe")
)
mesh <- fm_rcdt_2d_inla(globe = 2, crs = fm_crs("sphere"))

## 2 vertices found in the polygon
fm_contains(obj, mesh, type = "vertex")
#> Sparse geometry binary predicate list of length 1, where the predicate
#> was `contains'
#>  1: 8, 17

## 3 triangles found in the polygon
fm_contains(obj, mesh)
#> Sparse geometry binary predicate list of length 1, where the predicate
#> was `contains'
#>  1: 15, 18, 35

## Multiple transformations can lead to slightly different results
## due to edge cases:
## 4 triangles found in the polygon
fm_contains(
  obj,
  fm_transform(mesh, crs = fm_crs("mollweide_norm"))
)
#> Sparse geometry binary predicate list of length 1, where the predicate
#> was `contains'
#>  1: 7, 15, 18, 35