Compute the left unit normal of the directed segment A->B

Returns the unit-length normal vector pointing to the left of the directed segment \(A \rightarrow B\). For a direction vector \(v = (vx, vy)\), the left normal is \((-vy, vx)\) normalized by \(||v||\).

Usage

unit_normal_left(A, B)

Arguments

A

A data frame with columns `x` and `y` representing point A. If it contains multiple rows, only the first row is used.

B

A data frame with columns `x` and `y` representing point B. If it contains multiple rows, only the first row is used.

Value

A numeric vector of length 2 with named components:

nx

x-component of the left unit normal.

ny

y-component of the left unit normal.

Examples

# Horizontal segment to the right: (0,0) -> (1,0)
#    Left normal points upward: (0, 1)
A <- data.frame(x = 0, y = 0)
B <- data.frame(x = 1, y = 0)
unit_normal_left(A, B)
#> nx ny 
#>  0  1