perpproj: Perpendicular Projection

Description

Perpendicular Projection in two-dimensions

Usage

perpproj(V1, V2, add = FALSE)

Arguments

vector 1

add

logical, TRUE add to plot

Value

list:
P1x, y
P2x, y

Details

V1 and V2 are arrays with, for example, V1=c(x1 , x2 , y1, y2) or lists with V2=list(x=c(x1, x2), y-c(y1, y2)) which gets converted into the first format.

The points are from the head of each vector projected onto the the line formed by the other vector. If the the x1 y1 of each vector do not coincide, the interesections of two lines is determined and the tail of each vector is moved to that point for determining the projection positions.

Examples

Run this code

V1 = c( 2,  6, 1, 9)
    V2 = c( 0, 5,  1, 2)

  
    PP = perpproj( V1, V2, add=FALSE  )


    R = range(c(V1, V2, unlist(PP) ))

    plot(R, R, type='n', asp=1)

    arrows(V1[1], V1[3], V1[2], V1[4], length=.08 ) 
   arrows(V2[1], V2[3], V2[2], V2[4], length=.08 ) 

    points(PP$P1[1],PP$P1[2], col='red')
       points(PP$P2[1],PP$P2[2], col='blue')



    arrows(V2[2], V2[4],PP$P1[1],PP$P1[2] , length=.08, col='red' )
    
    arrows(V1[2], V1[4], PP$P2[1],PP$P2[2], length=.08, col='blue' )