3D Mesh Plot with Alphahull

Mix.install([
  {:plotly_ex, "~> 0.3"},
  {:kino, "~> 0.18"}
])

Section

alphahull: controls how tightly the mesh wraps around the point cloud. alphahull: 0 = convex hull (loosest possible mesh). Larger values = tighter wrapping that can capture concave features. Here we show the same point cloud with two different alphahull values side by side using subplots.

alias Plotly.{Figure, Mesh3d}

# Same random sphere points for both
n = 80
:rand.seed(:exsplus, {1, 2, 3})

{xs, ys, zs} =
  Enum.reduce(1..n, {[], [], []}, fn _, {xs, ys, zs} ->
    theta = :rand.uniform() * 2 * :math.pi()
    phi = :rand.uniform() * :math.pi()
    {[:math.sin(phi) * :math.cos(theta) | xs],
     [:math.sin(phi) * :math.sin(theta) | ys],
     [:math.cos(phi) | zs]}
  end)

Figure.new()
|> Figure.add_trace(
  Mesh3d.new(x: xs, y: ys, z: zs, alphahull: 0, color: "cyan", opacity: 0.5,
             name: "alphahull=0 (convex)", scene: "scene")
)
|> Figure.add_trace(
  Mesh3d.new(x: xs, y: ys, z: zs, alphahull: 7, color: "magenta", opacity: 0.5,
             name: "alphahull=7 (tight)", scene: "scene2")
)
|> Figure.update_layout(
  title: "Alphahull Comparison",
  scene: %{domain: %{x: [0, 0.5]}, xaxis: %{title: "X"}, yaxis: %{title: "Y"}, zaxis: %{title: "Z"}},
  scene2: %{domain: %{x: [0.5, 1]}, xaxis: %{title: "X"}, yaxis: %{title: "Y"}, zaxis: %{title: "Z"}}
)
|> Plotly.show()