transform_matrix_affine: generate a 3*3 matrix for affine transformation

In zzwch/crosslink: Visualize the Network of Grouped Nodes

generate a 3*3 matrix for affine transformation

Description

learn more about 2D affine and perspective tranformation matrix:

• https://en.wikipedia.org/wiki/Transformation_matrix

• https://www.cnblogs.com/bnuvincent/p/6691189.html

• Rconic::`Affine planar transformations matrix`

Used arguments for different types:

• none: ignore everything

• translate: x, y, counterclockwise

• scale: x, y, scale.x, scale.y

• scale_xy: x, y

• rotate: x, y, theta (angle of the rotation), counterclockwise

• shear: x, y, counterclockwise

• reflect: x, y, theta (angle from x axis), counterclockwise

Usage

transform_matrix_affine(
  type = c("none", "translate", "scale", "rotate", "shear", "reflect"),
  x = 0,
  y = 0,
  theta = NA,
  scale.x = 1,
  scale.y = 1,
  counterclockwise = FALSE
)

Arguments

type	a affine transformation type
x	transform value along x axis
y	transform value along y axis
theta	transform value of angle in radian, usually in 0 to 2pi
scale.x, scale.y	scale size, only used for scale type
counterclockwise	control directions of theta or x,y if type is "shear"

Value

a 3*3 matrix

Examples

# eigen matrix
transform_matrix_affine(type = "none")

# shift matrix for convert c(0, 0) to c(1, 2)
mat <- transform_matrix_affine(type = "translate", x = 1, y = 2)
mat %*% c(0, 0, 1)

# rotation matrix for convert c(0, 0) to c(0, 2)
mat <- transform_matrix_affine(type = "rotate", x = 1, y = 1, theta = pi/2)
mat %*% c(0, 0, 1)

# shear for convert c(1, 1) to c(2, 1) if along x or c(1, 2) if along y
mat <- transform_matrix_affine(type = "shear", x = pi*45/180, y = 0)
mat <- transform_matrix_affine(type = "shear", x = 0, y = pi*45/180, counterclockwise = T)

# reflect for convert c(0, 0) to c(2, 2)
mat <- transform_matrix_affine(type = "reflect", x = 1, y = 1, theta = pi*45/180)

zzwch/crosslink documentation built on Aug. 27, 2023, 5:57 p.m.