Draw a polygon in three dimensions

This function takes a description of a flat polygon in x, y and z coordinates, and draws it in three dimensions.

Usage

polygon3d(x, y = NULL, z = NULL, fill = TRUE, plot = TRUE, 
          coords, random = TRUE, ...)

Arguments

x, y, z

Vertices of the polygon in a form accepted by xyz.coords.

fill

logical; should the polygon be filled?

plot

logical; should the polygon be displayed?

coords

Which two coordinates (x = 1, y = 2, z = 3) describe the polygon. If missing, triangulate makes an automatic choice.

random

Currently ignored. The triangulation is deterministic.

...

Other parameters to pass to lines3d or shade3d if plot = TRUE.

Details

The function triangulates the two dimensional polygon described by coords, then applies the triangulation to all three coordinates. No check is made that the polygon is actually all in one plane, but the results may be somewhat unpredictable (especially if random = TRUE) if it is not.

Polygons need not be simple; use NA to indicate separate closed pieces. For fill = FALSE there are no other restrictions on the pieces, but for fill = TRUE the resulting two-dimensional polygon needs to be one that triangulate can handle.

Value

If plot = TRUE, the id number of the lines (for fill = FALSE) or triangles (for fill = TRUE) that have been plotted.

If plot = FALSE, then for fill = FALSE, a vector of indices into the XYZ matrix that could be used to draw the polygon. For fill = TRUE, a triangular mesh object representing the triangulation.

Author

Duncan Murdoch

See also

extrude3d for a solid extrusion of a polygon, triangulate for the triangulation.

Examples

theta <- seq(0, 4*pi, length.out = 50)
r <- theta + 1
r <- c(r[-50], rev(theta*0.8) + 1)
theta <- c(theta[-50], rev(theta))
x <- r*cos(theta)
y <- r*sin(theta)
open3d()
plot(x, y, type = "n")
polygon(x, y)

polygon3d(x, y, x + y, col = "blue")