Apply Geometric Transformations to Coordinates

Applies scaling, rotation, and translation to a set of 2D coordinates. The transformations are applied in the following order:

1. Scaling

2. Rotation (see rotate())

3. Translation

Usage

transformXY(
  x,
  y = NULL,
  translate = c(0, 0),
  scale = c(1, 1),
  theta = 0,
  asp = 1
)

Arguments

x

numeric vector of x coordinates, or an object coercible by xy.coords().

y

numeric vector of y coordinates. Ignored if x already contains both coordinates.

translate

numeric vector of length 1 or 2 specifying translation in x and y direction. Recycled if necessary. Default is c(0, 0).

scale

numeric vector of length 1 or 2 specifying scaling factors for x and y. Recycled if necessary. Default is c(1, 1).

theta

rotation angle in radians. Default is 0.

asp

aspect ratio adjustment passed to rotate(). Default is 1.

Value

A list with components x and y, as returned by xy.coords().

Details

This function is a convenience wrapper combining basic affine transformations. Internally, it uses rotate() for rotation.

See also

Other geometry.transformation: rotate()

Examples

x <- c(0, 1, 1, 0)
y <- c(0, 0, 1, 1)

# scale, rotate and translate a square
transformXY(x, y,
            scale = 2,
            theta = pi / 4,
            translate = c(1, 1))
#> $x
#> [1] 2.0000000 3.4142136 2.0000000 0.5857864
#> 
#> $y
#> [1] 0.5857864 2.0000000 3.4142136 2.0000000
#> 
#> $xlab
#> NULL
#> 
#> $ylab
#> NULL
#> 

# matrix input
m <- cbind(x, y)
transformXY(m, scale = 0.5, theta = pi/6)
#> $x
#> [1]  0.15849365  0.59150635  0.34150635 -0.09150635
#> 
#> $y
#> [1] -0.09150635  0.15849365  0.59150635  0.34150635
#> 
#> $xlab
#> NULL
#> 
#> $ylab
#> NULL
#>