R: The line at a point 'p' parallel to the line segment joining...

paraline {pcds}

R Documentation

The line at a point `p` parallel to the line segment joining two distinct 2D points `a` and `b`

Description

An object of class "Lines". Returns the equation, slope, intercept, and y-coordinates of the line crossing the point p and parallel to the line passing through the points a and b with x-coordinates are provided in vector x.

Usage

paraline(p, a, b, x)

Arguments

`p`	A 2D point at which the parallel line to line segment joining `a` and `b` crosses.
`a`, `b`	2D points that determine the line segment (the line will be parallel to this line segment).
`x`	A scalar or a `vector` of scalars representing the `x`-coordinates of the line parallel to `ab` and crossing `p`.

Value

A list with the elements

`desc`	Description of the line passing through point `p` and parallel to line segment joining `a` and `b`
`mtitle`	The `"main"` title for the plot of the line passing through point `p` and parallel to line segment joining `a` and `b`
`points`	The input points `p`, `a`, and `b` (stacked row-wise, i.e., point `p` is in row 1, point `a` is in row 2 and point `b` is in row 3). Line parallel to `ab` crosses p.
`x`	The input vector. It can be a scalar or a `vector` of scalars, which constitute the `x`-coordinates of the point(s) of interest on the line passing through point `p` and parallel to line segment joining `a` and `b`.
`y`	The output scalar or `vector` which constitutes the `y`-coordinates of the point(s) of interest on the line passing through point `p` and parallel to line segment joining `a` and `b`. If `x` is a scalar, then `y` will be a scalar and if `x` is a `vector` of scalars, then `y` will be a `vector` of scalars.
`slope`	Slope of the line, `Inf` is allowed, passing through point `p` and parallel to line segment joining `a` and `b`
`intercept`	Intercept of the line passing through point `p` and parallel to line segment joining `a` and `b`
`equation`	Equation of the line passing through point `p` and parallel to line segment joining `a` and `b`

Author(s)

Elvan Ceyhan

Examples


A<-c(1.1,1.2); B<-c(2.3,3.4); p<-c(.51,2.5)

paraline(p,A,B,.45)

pts<-rbind(A,B,p)
xr<-range(pts[,1])
xf<-(xr[2]-xr[1])*.25
#how far to go at the lower and upper ends in the x-coordinate
x<-seq(xr[1]-xf,xr[2]+xf,l=5)  #try also l=10, 20, or 100

plnAB<-paraline(p,A,B,x)
plnAB
summary(plnAB)
plot(plnAB)

y<-plnAB$y
Xlim<-range(x,pts[,1])
if (!is.na(y[1])) {Ylim<-range(y,pts[,2])} else {Ylim<-range(pts[,2])}
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]
pf<-c(xd,-yd)*.025

plot(A,pch=".",xlab="",ylab="",main="Line Crossing P and Parallel to AB",
xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05))
points(pts)
txt.str<-c("A","B","p")
text(pts+rbind(pf,pf,pf),txt.str)

segments(A[1],A[2],B[1],B[2],lty=2)
if (!is.na(y[1])) {lines(x,y,type="l",lty=1,xlim=Xlim,ylim=Ylim)} else {abline(v=p[1])}
tx<-(A[1]+B[1])/2;
if (!is.na(y[1])) {ty<-paraline(p,A,B,tx)$y} else {ty=p[2]}
text(tx,ty,"line parallel to AB\n and crossing p")

[Package pcds version 0.1.8 Index]

The line at a point p parallel to the line segment joining two distinct 2D points a and b