Rotate a Geometric Structure

Rotate a geometric structure by an angle theta around a centerpoint xy. 

Rotate(x, y = NULL, mx = NULL, my = NULL, theta = pi/3, asp = 1)

Arguments

x, y

vectors containing the coordinates of the vertices of the polygon , which has to be rotated. The coordinates can be passed in a plotting structure (a list with x and y components), a two-column matrix, .... See xy.coords.

mx, my

xy-coordinates of the center of the rotation. If left to NULL, the centroid of the structure will be used.

theta

angle of the rotation

asp

the aspect ratio for the rotation. Helpful for rotate structures along an ellipse.

Value

The function invisibly returns a list of the coordinates for the rotated shape(s).

Author

Andri Signorell <andri@signorell.net>

Examples

# let's have a triangle
Canvas(main="Rotation")
x <- DrawRegPolygon(nv=3)[[1]]

# and rotate
sapply( (0:3) * pi/6, function(theta) {
  xy <- Rotate( x=x, theta=theta )
  polygon(xy, col=SetAlpha("blue", 0.2))
} )
#> [[1]]
#> NULL
#> 
#> [[2]]
#> NULL
#> 
#> [[3]]
#> NULL
#> 
#> [[4]]
#> NULL
#> 

abline(v=0, h=0)