angle.str2end: The angles to draw arcs between two line segments

Description

Gives the two pairs of angles in radians or degrees to draw arcs between two vectors or line segments for the draw.arc function in the plotrix package. The angles are provided with respect to the \(x\)-axis in the coordinate system. The line segments are \([ba]\) and \([bc]\) when the argument is given as a,b,c in the function.

radian is a logical argument (default=TRUE) which yields the angle in radians if TRUE, and in degrees if FALSE. The first pair of angles is for drawing arcs in the smaller angle between \([ba]\) and \([bc]\) and the second pair of angles is for drawing arcs in the counter-clockwise order from \([ba]\) to \([bc]\).

Usage

angle.str2end(a, b, c, radian = TRUE)

Value

A list with two elements

small.arc.angles: Angles of \([ba]\) and \([bc]\) with the \(x\)-axis so that difference between them is the smaller angle between \([ba]\) and \([bc]\)
ccw.arc.angles: Angles of \([ba]\) and \([bc]\) with the \(x\)-axis so that difference between them is the counter-clockwise angle between \([ba]\) and \([bc]\)

Arguments

a, b, c: Three 2D points which represent the intersecting line segments \([ba]\) and \([bc]\).
radian: A logical argument (default=TRUE). If TRUE, the smaller angle or counter-clockwise angle between the line segments \([ba]\) and \([bc]\) is provided in radians, else it is provided in degrees.

Author

Elvan Ceyhan

Examples

Run this code

# \donttest{
A<-c(.3,.2); B<-c(.6,.3); C<-c(1,1)

pts<-rbind(A,B,C)

Xp<-c(B[1]+max(abs(C[1]-B[1]),abs(A[1]-B[1])),0)

angle.str2end(A,B,C)
angle.str2end(A,B,A)

angle.str2end(A,B,C,radian=FALSE)

#plot of the line segments
ang.rad<-angle.str2end(A,B,C,radian=TRUE); ang.rad
ang.deg<-angle.str2end(A,B,C,radian=FALSE); ang.deg
ang.deg1<-ang.deg$s; ang.deg1
ang.deg2<-ang.deg$c; ang.deg2

rad<-min(Dist(A,B),Dist(B,C))

Xlim<-range(pts[,1],Xp[1],B+Xp,B[1]+c(+rad,-rad))
Ylim<-range(pts[,2],B[2]+c(+rad,-rad))
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]

#plot for the smaller arc
plot(pts,pch=1,asp=1,xlab="x",ylab="y",xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05))
L<-rbind(B,B,B); R<-rbind(A,C,B+Xp)
segments(L[,1], L[,2], R[,1], R[,2], lty=2)
plotrix::draw.arc(B[1],B[2],radius=.3*rad,angle1=ang.rad$s[1],angle2=ang.rad$s[2])
plotrix::draw.arc(B[1],B[2],radius=.6*rad,angle1=0, angle2=ang.rad$s[1],lty=2,col=2)
plotrix::draw.arc(B[1],B[2],radius=.9*rad,angle1=0,angle2=ang.rad$s[2],col=3)
txt<-rbind(A,B,C)
text(txt+cbind(rep(xd*.02,nrow(txt)),rep(-xd*.02,nrow(txt))),c("A","B","C"))

text(rbind(B)+.5*rad*c(cos(mean(ang.rad$s)),sin(mean(ang.rad$s))),
     paste(abs(round(ang.deg1[2]-ang.deg1[1],2))," degrees",sep=""))
text(rbind(B)+.6*rad*c(cos(ang.rad$s[1]/2),sin(ang.rad$s[1]/2)),paste(round(ang.deg1[1],2)),col=2)
text(rbind(B)+.9*rad*c(cos(ang.rad$s[2]/2),sin(ang.rad$s[2]/2)),paste(round(ang.deg1[2],2)),col=3)

#plot for the counter-clockwise arc
plot(pts,pch=1,asp=1,xlab="x",ylab="y",xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05))
L<-rbind(B,B,B); R<-rbind(A,C,B+Xp)
segments(L[,1], L[,2], R[,1], R[,2], lty=2)
plotrix::draw.arc(B[1],B[2],radius=.3*rad,angle1=ang.rad$c[1],angle2=ang.rad$c[2])
plotrix::draw.arc(B[1],B[2],radius=.6*rad,angle1=0, angle2=ang.rad$s[1],lty=2,col=2)
plotrix::draw.arc(B[1],B[2],radius=.9*rad,angle1=0,angle2=ang.rad$s[2],col=3)
txt<-pts
text(txt+cbind(rep(xd*.02,nrow(txt)),rep(-xd*.02,nrow(txt))),c("A","B","C"))

text(rbind(B)+.5*rad*c(cos(mean(ang.rad$c)),sin(mean(ang.rad$c))),
     paste(abs(round(ang.deg2[2]-ang.deg2[1],2))," degrees",sep=""))
text(rbind(B)+.6*rad*c(cos(ang.rad$s[1]/2),sin(ang.rad$s[1]/2)),paste(round(ang.deg1[1],2)),col=2)
text(rbind(B)+.9*rad*c(cos(ang.rad$s[2]/2),sin(ang.rad$s[2]/2)),paste(round(ang.deg1[2],2)),col=3)
# }