Unable to plot a sphere surface using Plots package

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1

I am trying to follow a tutorial on youtube for SVD, and the instructor created a sphere using Python. I am trying to translate the code to Julia

n = 100
u = range(-π, π; length = n)
v = range(0, π; length = n)
x = cos.(u) * sin.(v)'
y = sin.(u) * sin.(v)'
z = ones(n) * cos.(v)'

surface(x, y, z)

But i get this error

Failed to show value:
MethodError: Cannot `convert` an object of type Plots.Surface{Matrix{Float64}} to an object of type Vector{Float64}

However when i use plot(x, y, z) it plots a hundred circles
image

The original code is from this video
How can I plot a sphere surface?
Thanks

2

Using Plots.jl plotly() backend, see this solution.

3

its not possible with GR backend?

4

Do not think that gr() handles parametric surfaces in 3D (Makie is best for that).

5

Thank you. I used plotly() with the same code, but my plot’s ticks are all zeros. Do i have to manually set the ticks? Why it couldn’t be done automatically, or am I missing something?

# using Pkg; Pkg.add("Plotly")
using Plots

n = 100
u = range(-π, π; length = n)
v = range(0, π; length = n)
x = cos.(u) * sin.(v)'
y = sin.(u) * sin.(v)'
z = ones(n) * cos.(v)'

plotly()
surface(x, y, z)

image

6

This might be widespread issue introduced in Julia 1.6.1 while using older Plots.jl versions.

2 Likes
7

Thanks a lot!!! Actually you are 100% correct.
It looks like i had installed a pacakge FourierAnalysis which forced my Pkg to install a very old version of Plots, and wouldn’t allow me to upgrade it. I removed the FourierAnalysis package and finally was able to update plots, and the axes are now correct. Thanks!!
I think I understand now why I should activate a new environment in each new project directory!
Thanks

1 Like
8

Just for the record, a decent sphere can be produced with Plots.jl gr() back-end by splitting it in two (top and bottom surfaces). However, it requires a careful computation of the end points for a nice stitching job and minding the plotting order.

using Plots; gr()

zplus(x,y) = (x^2 + y^2) <= 1 ? sqrt.(abs.(1.0 .- x.^2 .- y.^2)) : NaN
zminus(x,y) = (x^2 + y^2) <= 1 ? -sqrt.(abs.(1.0 .- x.^2 .- y.^2)) : NaN

x = collect(-1:0.01:1);
y = @. (1-x^2)^0.5
y = reshape(permutedims([-y y]),:,1)[:]
x = sort([x; x.+eps()])

surface(x,y,zminus, ratio=:equal,xlims=(-1,1),ylims=(-1,1),zlims=(-1,1))  # isometric
surface!(x,y,zplus, ratio=:equal,xlims=(-1,1),ylims=(-1,1),zlims=(-1,1))  # isometric

Plots_gr_sphere_2_halves

1 Like