The triangles of cells towards each neighbour

Cuts each cell into one triangle per wall, from the centre to that wall: six for a hexagon, five for a pentagon. With values, each triangle carries the change from its cell's value to the neighbour's across the wall, so colouring the triangles shows the change from cell to cell in every direction (Carr et al. 1997, after K. and R. Keister).

Usage

hex_triangles(cell_id, grid, value = NULL)

Arguments

cell_id

Cell IDs, each listed once.

grid

A HexGridInfo or HexData object.

value

Optional values, one per cell. A neighbour not in cell_id or with an NA value gives an NA change.

Value

An sf object of POLYGONs with columns cell_id, neighbor_id and, with values, value, neighbor_value and change (neighbor_value - value).

References

Carr, D. B., Kahn, R., Sahr, K., Olsen, A. R. (1997). ISEA discrete global grids. Statistical Computing & Graphics Newsletter 8(2/3): 31-39.

See also

hex_rays, get_neighbors, wall_metrics

Examples

g <- hex_grid(resolution = 3, aperture = 3)
cells <- grid_rect(c(0, 40, 30, 60), g)$cell_id
ctr <- cell_to_lonlat(cells, g)
tri <- hex_triangles(cells, g, value = ctr$lat_deg)
plot(tri["change"], border = NA)