CODEWITHSUNDEEP
rmatlab
Bensstats
Bensstats

Reputation: 1056

What is the R equivalent of Matlab's `sphere()` function

I am trying to replicate some Matlab code in R and I have been looking around for an R equivalent of Matlab's sphere() function.

For reference the sphere() function documentation is here.

For clarification, I am interested in the actual assignment properties of sphere(). Namely I am interested in knowing how to write

[X,Y,Z]=sphere(200)

In R.

Upvotes: 1

Views: 119

Answers (2)

Ben Bolker
Ben Bolker

Reputation: 226182

How about:

library(geometry)
sphere <- function(n) {
   dd <- expand.grid(theta = seq(0, 2*pi, length.out = n+1)[-1],
                     phi = seq(-pi, pi, length.out = n+1)[-1])
   sph2cart(dd$theta, dd$phi, r = 1)
}

Really you don't need the geometry package either, as the payload of geometry::sphere2cart is just

x <- r * cos(phi) * cos(theta)
y <- r * cos(phi) * sin(theta)
z <- r * sin(phi)

The other 20-odd lines of code are argument-processing and error-checking. So you could put together your own self-contained function using just expand.grid and the three lines of geometry.

Take 2: return a list of 3, (n+1 x n+1) matrices.

sphere <- function(n) {
   dd <- expand.grid(theta = seq(0, 2*pi, length.out = n+1),
                     phi = seq(-pi, pi, length.out = n+1))
   with(dd, 
        list(x = matrix(cos(phi) * cos(theta), n+1),
             y = matrix(cos(phi) * sin(theta), n+1),
             z = matrix(sin(phi), n+1))
        )
}

This will return a list of matrices with names x, y, z, not assign values to variables in the calling environment ... that's difficult/non-idiomatic in R.

Upvotes: 3

Allan Cameron
Allan Cameron

Reputation: 173813

This looks fairly similar to spheresurf3D from the plot3D package

library(plot3D)

spheresurf3D(bty = "b", ticktype = "detailed", phi = 30, theta = 135,
             shade = 0.5, border = "black", col = jet.col()[1:75])

enter image description here

Upvotes: 2

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