`isosurface`

Extracts the surface where 3-D volume data equals a chosen value, as faces and vertices.

Syntax

fv = isosurface(X, Y, Z, V, isovalue)

Returns a structure with faces and vertices for the surface V = isovalue on the grid (X, Y, Z).

fv = isosurface(V, isovalue)

Uses the grid 1:n in each direction.

[f, v] = isosurface(___)

Returns faces and vertices as two arrays.

Description

The function is the 3-D analog of a contour line. It walks through the cells of the volume and builds triangles wherever the data crosses the isovalue. The vertex positions are linearly interpolated between grid points.

Draw the result with patch(fv, 'FaceColor', 'r'), then add view(3) and camlight for a lit 3-D look.

Input arguments

X, Y, Z: Coordinate arrays, as from meshgrid.
V: 3-D array of scalar data.
isovalue: The level at which to cut the data.

Output arguments

fv: Structure with vertices (n-by-3) and faces (m-by-3 triangles indexing the vertices), ready for patch.
f, v: The faces and the vertices as separate arrays.

Example

Sphere from a distance field

[x, y, z] = meshgrid(-1:0.5:1);
v = x.^2 + y.^2 + z.^2;
fv = isosurface(x, y, z, v, 0.5);
size(fv.faces)
size(fv.vertices)
max(fv.vertices)

Output

ans = 1×2

    96     3
ans = 1×2

    74     3
ans = 1×3

    0.6667    0.6667    0.6667

isosurface