[R] plotting an isosurface on a 3d plot

[Duncan Murdoch]

On 13/06/2019 12:47 p.m., ravi via R-help wrote:
> Hi,I want to plot a surface joining a circle on a plane with another circle (a little offset w.r.t. the first one) on a parallel plane. This is a very simplified version of my problem.
> I will explain with the following code :
> # First, I plot the two circlesorig1 <- 0.4;radius1=0.3;theta <- seq(0,2*pi,pi/8)x1 <- orig1+radius1*cos(theta)y1 <- orig1+radius1*sin(theta)
> orig2 <- 0.7;radius2=0.2;theta <- seq(0,2*pi,pi/8)x2 <- orig2+radius2*cos(theta)y2 <- orig2+radius2*sin(theta)
> plot(x1,y1,type='b',col="red",xlim=c(0,1),ylim=c(0,1),asp=1)lines(x2,y2,type="b",col="blue")
> #### the z coordinates on two parallel plnesz1 <- rep(0,length(x1))z2 <- rep(1,length(x2))
> 
> I have tried to plot my 3d figure using the packages plot3D, misc3d, rgl etc. All these packages require z as a matrix. In my case, all of x,y and z are vectors. How can I plot this surface? In addition, I would like to add similiar surfaces to the same plot.

It's not true that rgl requires z as a matrix:  that's one possibility, 
but there are others.  Here's one way to do what you want.

# First, compute the two circles
orig1 <- 0.4;radius1=0.3;theta <- seq(0,2*pi,pi/8)
x1 <- orig1+radius1*cos(theta)
y1 <- orig1+radius1*sin(theta)
orig2 <- 0.7;radius2=0.2
x2 <- orig2+radius2*cos(theta)
y2 <- orig2+radius2*sin(theta)

#### the z coordinates on two parallel plnes
z1 <- rep(0,length(x1))
z2 <- rep(1,length(x2))

library(rgl)
p1 <- cbind(x1,y1,z1)
plot3d(p1, col="red")
p2 <- cbind(x2, y2, z2)
points3d(p2, col="blue")

quads <- matrix(numeric(), 0, 3)
for (i in seq_along(x1)[-1]) {
   quads <- rbind(quads, p1[i-1,], p1[i,], p2[i,], p2[i-1,])
}
quads3d(quads, col = "green")

There are more efficient ways to do this (the for loop would be slow if 
you had bigger vectors), but this should give you the idea.

Duncan Murdoch