Draws one ray per cell from its centre whose angle shows a value, as in Carr et al. (1997): the ray points down for the smallest value, level for the middle of the range and up for the largest. A confidence arc at the ray's tip spans the angles of a lower and an upper bound. A second variable gets a ray of its own pointing to the left from the same centre, so one glyph shows two values.
Usage
hex_rays(
cell_id,
value,
grid,
lower = NULL,
upper = NULL,
value2 = NULL,
lower2 = NULL,
upper2 = NULL,
limits = NULL,
limits2 = NULL,
length = 0.85
)Arguments
- cell_id
Cell IDs, each listed once.
- value
Values shown by the right-hand rays.
- grid
A HexGridInfo or HexData object.
- lower, upper
Optional bounds of
value(such as a confidence interval), drawn as an arc at the tip of the ray.- value2, lower2, upper2
Optional second variable and its bounds, drawn to the left.
- limits
Values drawn straight down and straight up:
c(min, max).NULLuses the range of the values and bounds; with a second variable both share it unlesslimits2is given.- limits2
Limits of the second variable.
- length
Length of a ray as a fraction of the distance from the cell centre to the middle of a wall.
Value
An sf object of LINESTRINGs with columns cell_id,
side ("right" or "left") and part
("ray" or "arc").
Details
Rays run in the plane tangent to the sphere at the cell centre, with up towards north, and are returned as lines in longitude and latitude, ready for any map of the cells.
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_triangles for the change towards each
neighbour
Examples
g <- hex_grid(resolution = 4, aperture = 3)
cells <- lonlat_to_cell(c(5, 10, 15), c(45, 47, 49), g)
trend <- c(-1, 0.2, 1.4)
rays <- hex_rays(cells, trend, g, lower = trend - 0.5, upper = trend + 0.5)
plot(sf::st_geometry(cell_to_sf(cells, g)))
plot(sf::st_geometry(rays), add = TRUE, col = "#D55E00")