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Create hexagon lattice points

Source: R/mesh_2d.R
fm_hexagon_lattice.Rd

[Experimental] from 0.3.0.9001. Create hexagon lattice points within a boundary. By default, the hexagonal lattice is anchored at the coordinate system origin, so that grids with different but overlapping boundaries will have matching points.

Usage

fm_hexagon_lattice(
  bnd,
  edge_len = NULL,
  buffer_n = 0.49,
  align = "origin",
  meta = FALSE
)

Arguments

bnd

Boundary object (currently must be an sf polygon)

edge_len

Triangle edge length. Default diff(fm_bbox(bnd)[[1]]) / 250.

buffer_n

Number of triangle height multiples for buffer inside the boundary object to the start of the lattice. Default 0.49.

align

Alignment of the hexagon lattice, either a length-2 numeric, or character, a sf/sfc/sfg object containing a single point), or character, default "origin":

"origin"

align the lattice with the coordinate system origin

"bbox"

align the lattice with the midpoint of the bounding box of bnd

"centroid"

align the lattice with the centroid of the boundary, sf::st_centroid(bnd)

meta

logical; if TRUE, return a list with diagnostic information from the lattice construction (including the points themselves in lattice)

Value

An sfc object with points, if meta is FALSE (default), or if meta=TRUE, a list:

lattice

sfc with lattice points

edge_len

numeric with edge length

bnd_inner

sf object with the inner boundary used to filter points outside of a edge_len * buffer_n distance from the boundary

grid_n

integer with the number of points in each direction prior to filtering

align

numeric with the alignment coordinates of the hexagon lattice

See also

fm_mesh_2d()

Author

Man Ho Suen M.H.Suen@sms.ed.ac.uk, Finn Lindgren Finn.Lindgren@gmail.com

Examples

(m <- fm_mesh_2d(
  fm_hexagon_lattice(
    fmexample$boundary_sf[[1]],
    edge_len = 0.1 * 5
  ),
  max.edge = c(0.2, 1) * 5,
  boundary = fmexample$boundary_sf
))
#> fm_mesh_2d object:
#>   Manifold:	R2
#>   V / E / T:	189 / 537 / 349
#>   Euler char.:	1
#>   Constraints:	Boundary: 27 boundary edges (1 group: 1), Interior: 49 interior edges (1 group: 1)
#>   Bounding box: (-5.331027, 4.061656) x (-3.998161, 5.415609)
#>   Basis d.o.f.:	189

(m2 <- fm_mesh_2d(
  fm_hexagon_lattice(
    fmexample$boundary_sf[[1]],
    edge_len = 0.1 * 5,
    align = "centroid"
  ),
  max.edge = c(0.2, 1) * 5,
  boundary = fmexample$boundary_sf
))
#> fm_mesh_2d object:
#>   Manifold:	R2
#>   V / E / T:	195 / 554 / 360
#>   Euler char.:	1
#>   Constraints:	Boundary: 28 boundary edges (1 group: 1), Interior: 50 interior edges (1 group: 1)
#>   Bounding box: (-5.331027, 4.061656) x (-3.998161, 5.415609)
#>   Basis d.o.f.:	195

if (require("ggplot2", quietly = TRUE) &&
  require("patchwork", quietly = TRUE)) {
  ((ggplot() +
    geom_fm(data = m) +
    geom_point(aes(0, 0), col = "red")) |
    (ggplot() +
      geom_fm(data = m2) +
      geom_point(aes(0, 0), col = "red") +
      geom_sf(data = sf::st_centroid(fmexample$boundary_sf[[1]]))
    )
  )
}