pcds (version 0.1.4)

rv.triCM: The index of the \(CM\)-vertex region in a triangle that contains a given point

Description

Returns the index of the vertex whose region contains point p in the triangle tri\(=(y_1,y_2,y_3)\) with vertex regions are constructed with center of mass \(CM=(y_1+y_2+y_3)/3\) (see the plots in the example for illustrations).

The vertices of triangle, tri, are labeled as \(1,2,3\) according to the row number the vertex is recorded in tri. If the point, p, is not inside tri, then the function yields NA as output. The corresponding vertex region is the polygon with the vertex, \(CM\), and midpoints of the edges adjacent to the vertex.

See (ceyhan:Phd-thesis,ceyhan:comp-geo-2010,ceyhan:mcap2012;textualpcds)

Usage

rv.triCM(p, tri)

Value

A list with two elements

rv

Index of the \(CM\)-vertex region that contains point, p in the triangle tri.

tri

The vertices of the triangle, where row number corresponds to the vertex index in rv.

Arguments

p

A 2D point for which \(CM\)-vertex region it resides in is to be determined in the triangle tri.

tri

Three 2D points, stacked row-wise, each row representing a vertex of the triangle.

Author

Elvan Ceyhan

References

See Also

rv.tri.cent, rv.triCC, rv.bastriCM, rv.bastriCC, rv.bastri.cent, and rvTeCM

Examples

A<-c(1,1); B<-c(2,0); C<-c(1.6,2);
Tr<-rbind(A,B,C);
P<-c(1.4,1.2)
rv.triCM(P,Tr)

P<-c(.8,.2)
rv.triCM(P,Tr)

P<-c(1.5,1.6)
rv.triCM(P,Tr)

n<-10  #try also n<-20
dat<-runif.tri(n,Tr)$g

Rv<-vector()
for (i in 1:n)
  Rv<-c(Rv,rv.triCM(dat[i,],Tr)$rv)
Rv

CM<-(A+B+C)/3
D1<-(B+C)/2; D2<-(A+C)/2; D3<-(A+B)/2;
Ds<-rbind(D1,D2,D3)

Xlim<-range(Tr[,1],dat[,1])
Ylim<-range(Tr[,2],dat[,2])
xd<-Xlim[2]-Xlim[1]
yd<-Ylim[2]-Ylim[1]

plot(Tr,xlab="",ylab="",axes=TRUE,pch=".",xlim=Xlim+xd*c(-.05,.05),ylim=Ylim+yd*c(-.05,.05))
polygon(Tr)
points(dat,pch=".")
L<-Ds; R<-matrix(rep(CM,3),ncol=2,byrow=TRUE)
segments(L[,1], L[,2], R[,1], R[,2], lty=2)
text(dat,labels=factor(Rv))

txt<-rbind(Tr,CM,D1,D2,D3)
xc<-txt[,1]+c(-.02,.02,.02,-.02,.02,-.01,-.01)
yc<-txt[,2]+c(-.02,-.04,.06,-.02,.02,.06,-.06)
txt.str<-c("rv=1","rv=2","rv=3","CM","D1","D2","D3")
text(xc,yc,txt.str)

rv.triCM(A,Tr)
rv.triCM(CM,Tr)
rv.triCM(D1,Tr)
rv.triCM(D2,Tr)
rv.triCM(D3,Tr)

#right triangle
A<-c(1,1); B<-c(1,2); C<-c(1.5,2);
T3<-rbind(A,B,C);
P<-c(1.1,1.5)
rv.triCM(P,T3)

#isosceles triangle
A<-c(1,1); B<-c(2,1); C<-c(1.5,2);
Tr<-rbind(A,B,C);
P<-c(1.5,1.1)
rv.triCM(P,Tr)

dat.fr<-data.frame(a=Tr)
rv.triCM(P,dat.fr)