Plot a grid on the sphere, on its solid, or on the unfolded net

Draws the cells of a grid in 3D, seen from above a chosen point: on the sphere, or on the flat faces of the solid the grid is built on. All surfaces take their cell boundaries from the same points, so a cell on the solid is the cell on the sphere folded flat.

Usage

# S4 method for class 'HexGridInfo,missing'
plot(
  x,
  y,
  surface = c("sphere", "solid", "net"),
  center = c(lon = 15, lat = 32),
  projection = c("orthographic", "perspective"),
  distance = NULL,
  tilt = 0,
  rotation = 0,
  fov = NULL,
  cells = NULL,
  land = TRUE,
  ocean_fill = "#F4F6F8",
  land_fill = "#C9D0D6",
  land_border = "#8C969F",
  land_lwd = 0.4,
  grid_border = "#0072B2",
  grid_lwd = 0.8,
  face_edges = NULL,
  edge_col = "black",
  edge_lwd = 1.1,
  layout = "plane",
  seams = FALSE,
  seam_col = "#D55E00",
  seam_lwd = 1.6,
  graticule = FALSE,
  graticule_col = "#9AA3AB",
  graticule_lwd = 0.5,
  distortion = c("none", "angular", "areal"),
  tissot = FALSE,
  tissot_col = "#2E3439",
  tissot_lwd = 0.8,
  parents = NULL,
  parent_col = "#1B2A38",
  parent_lwd = 1.8,
  area_legend = FALSE,
  tabs = FALSE,
  step = 0.01,
  main = NULL,
  ...
)

Arguments

x: A HexGridInfo object from hex_grid
y: Ignored
surface: "sphere", "solid" or "net". "solid" draws the flat faces of the grid's polyhedron (the icosahedron, or the octahedron of a grid built on it). The solid and the net need an ISEA grid; an H3 grid is drawn on the sphere.
center: Point the view looks down on: a preset name from globe_centers or c(lon, lat).
projection: "orthographic" or "perspective".
distance: Distance of the untilted perspective camera from the sphere's centre, in sphere radii; greater than 1. NULL uses 3. A geostationary satellite sits at about 6.6 Earth radii.
tilt: Degrees the perspective camera swings about the point at center, between -90 and 90, keeping its range of distance - 1 radii to that point. Positive values move the camera towards the bottom of the view, so it looks towards the top.
rotation: Degrees the view turns about the line of sight; positive values turn north clockwise.
fov: Field of view of the perspective camera in degrees, across the square the plot shows, centred on center; below 170. NULL frames the whole visible sphere instead.
cells: Cell IDs to draw. NULL draws every cell of the grid.
land: TRUE for the built-in hexify_world, FALSE for none, or an sf/sfc object of polygons.
ocean_fill: Fill colour of the surface.
land_fill: Fill colour of land; NA leaves land unfilled.
land_border: Colour of country outlines; NA draws none.
land_lwd: Line width of country outlines.
grid_border: Colour of cell boundaries.
grid_lwd: Line width of cell boundaries.
face_edges: Draw the edges of the solid's faces. NULL draws them for an ISEA grid; H3 is built on an icosahedron of its own, so its grid takes none.
edge_col: Colour of face edges.
edge_lwd: Line width of face edges.
layout: For surface = "net", the layout of the faces: a name net_layout takes, or a hexify_net object it built for this grid.
seams: For surface = "net", draw the cuts of the net: the sides of its pieces across which the map is not continuous, including its outline.
seam_col: Colour of seams.
seam_lwd: Line width of seams.
graticule: FALSE for none, TRUE for meridians and parallels every 30 degrees, or a number of degrees between them.
graticule_col: Colour of the graticule.
graticule_lwd: Line width of the graticule.
distortion: "none", "angular" for the maximum angular deformation of the face projection, or "areal" for its areal scale (1 everywhere on Snyder's equal-area projection). Needs an ISEA grid; a colour bar is drawn along the bottom.
tissot: FALSE for none, TRUE for Tissot ellipses at points about 30 degrees apart, or a number of degrees between them. Each ellipse is the image of a circle a fifth of that spacing in radius. Drawn on the net and the solid.
tissot_col: Colour of Tissot ellipses.
tissot_lwd: Line width of Tissot ellipses.
parents: Resolutions up whose cell outlines are drawn over the cells, such as 1 or 1:2; NULL for none.
parent_col: Colour of parent outlines, recycled over parents.
parent_lwd: Line width of parent outlines, recycled over parents.
area_legend: For surface = "net" of a grid on Snyder's equal-area projection, draw one hexagonal cell of each drawn resolution at the scale of the map, labelled with its area.
tabs: For surface = "net", draw glue tabs on the seams.
step: Spacing of the points along a cell boundary, as a fraction of a face edge.
main: Plot title.
...: Ignored

Value

The grid, invisibly

Details

surface = "net" lays the faces out flat, by default in the PLANE layout of DGGRID (hexify_cell_to_plane gives cell centres in the same coordinates); layout picks another, such as Van de Sande's Gosper World on the octahedron (see net_layout). A cell on a cut of the net is drawn in parts, one on each side. The net is drawn without a camera, so center, projection, distance, tilt, rotation and fov apply to the other two surfaces.

distortion colours the surface by the distortion of the face projection that maps the sphere onto the faces (see projection_distortion), and tissot draws Tissot's indicatrix on the faces: the ellipse each small circle of the sphere maps to. With graticule on the net, Snyder's projection shows small bends in the meridians and parallels where they cross the arcs from each face's centre to its corners.

parents draws the outlines of the cells some resolutions up over the grid's own cells, to show the hierarchy. On a net of an equal-area grid, area_legend draws one cell at the scale of the map, with its area, and the same for each resolution parents draws. tabs adds glue tabs along the seams of a net, one on each pair of edges glued together, so a printed net (for example through pdf) folds into the solid (Carr et al. 1997).

The view is an orthographic projection by default: parallel lines of sight, so the whole near half of the sphere shows. projection = "perspective" places a camera distance sphere radii from the sphere's centre, above center; it sees a smaller cap, and nearer cells appear larger. tilt swings that camera about the point at center, which it keeps looking at, so the surface is seen at a slant with the horizon towards the top; by default the plot frames the whole visible sphere. fov sets how wide the camera sees, and rotation turns the view about the line of sight in either projection.

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.

Examples

grid <- hex_grid(resolution = 3, aperture = 3)
plot(grid)
plot(grid, surface = "solid")
plot(grid, surface = "solid", land = FALSE, center = "pacific")
plot(grid, projection = "perspective", distance = 2, center = "europe")
plot(grid, surface = "solid", projection = "perspective",
     distance = 2.5, tilt = 25, rotation = 30)
plot(grid, surface = "net")
octa <- hex_grid(resolution = 3, aperture = 4, polyhedron = "octahedron",
                 orientation = "gosper")
plot(octa, surface = "net", layout = "gosper", seams = TRUE, graticule = TRUE)

# Distortion of the face projections, with Tissot's indicatrix
plot(grid, surface = "net", land = FALSE, distortion = "angular",
     tissot = TRUE, graticule = 15, cells = numeric(0))
fuller <- hex_grid(resolution = 3, aperture = 3, projection = "fuller")
plot(fuller, distortion = "areal", land = FALSE, cells = numeric(0))

# Two resolutions with an area legend, and a net to print and fold
fine <- hex_grid(resolution = 4, aperture = 3)
plot(fine, surface = "net", land = FALSE, parents = 1, area_legend = TRUE)
plot(grid, surface = "net", layout = "land", land = FALSE, seams = TRUE,
     tabs = TRUE)