1d:T754,# The angle between two line segments Returns the angle in radians or degrees between two vectors or line segments at the point of intersection. The line segments are $[ba]$ and $[bc]$ when the arguments of the function are given as `a,b,c`. `radian` is a logical argument (default=`TRUE`) which yields the angle in radians if `TRUE`, and in degrees if `FALSE`. The smaller of the angle between the line segments is provided by the function. ```r angle3pnts(a, b, c, radian = TRUE) ``` ## Arguments - `a, b, c`: Three 2D points which represent the intersecting line segments $[ba]$ and $[bc]$. The smaller angle between these line segments is to be computed. - `radian`: A logical argument (default=`TRUE`). If `TRUE`, the (smaller) angle between the line segments $[ba]$ and $[bc]$ is provided in radians, else it is provided in degrees. ## Returns angle in radians or degrees between the line segments $[ba]$ and $[bc]$ ## Examples ```r A<-c(.3,.2); B<-c(.6,.3); C<-c(1,1) pts<-rbind(A,B,C) angle3pnts(A,B,C) angle3pnts(A,B,A) round(angle3pnts(A,B,A),7) angle3pnts(A,B,C,radian=FALSE) #plot of the line segments Xlim<-range(pts[,1]) Ylim<-range(pts[,2]) xd<-Xlim[2]-Xlim[1] yd<-Ylim[2]-Ylim[1] ang1<-angle3pnts(A,B,C,radian=FALSE) ang2<-angle3pnts(B+c(1,0),B,C,radian=FALSE) sa<-angle.str2end(A,B,C,radian=FALSE)$s #small arc angles ang1<-sa[1] ang2<-sa[2] plot(pts,asp=1,pch=1,xlab="x",ylab="y", xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05)) L<-rbind(B,B); R<-rbind(A,C) segments(L[,1], L[,2], R[,1], R[,2], lty=2) plotrix::draw.arc(B[1],B[2],radius=xd*.1,deg1=ang1,deg2=ang2) txt<-rbind(A,B,C) text(txt+cbind(rep(xd*.05,nrow(txt)),rep(-xd*.02,nrow(txt))),c("A","B","C")) text(rbind(B)+.15*xd*c(cos(pi*(ang2+ang1)/360),sin(pi*(ang2+ang1)/360)), paste(round(abs(ang1-ang2),2)," degrees")) ``` ## See Also `angle.str2end` ## Author(s) Elvan Ceyhan

angle3pnts function