# The angles to draw arcs between two line segments 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 $[bc]$. ```r angle.str2end(a, b, c, radian = TRUE) ``` ## 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. ## Returns 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 $[bc]$ ## Examples ```r 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) ``` ## See Also `angle3pnts` ## Author(s) Elvan Ceyhan

angle.str2end function