Navigation

Operators and Keywords

Function List:

• » Octave core
• » by package
• » alphabetical

C++ API

: fv = isosurface (v, isoval)

: fv = isosurface (v)

: fv = isosurface (x, y, z, v, isoval)

: fv = isosurface (x, y, z, v)

: fvc = isosurface (…, col)

: fv = isosurface (…, "noshare")

: fv = isosurface (…, "verbose")

: [f, v] = isosurface (…)

: [f, v, c] = isosurface (…)

: isosurface (…)

Calculate isosurface of 3-D volume data.

An isosurface connects points with the same value and is analogous to a contour plot, but in three dimensions.

The input argument v is a three-dimensional array that contains data sampled over a volume.

The input isoval is a scalar that specifies the value for the isosurface. If isoval is omitted or empty, a "good" value for an isosurface is determined from v.

When called with a single output argument isosurface returns a structure array fv that contains the fields faces and vertices computed at the points [x, y, z] = meshgrid (1:l, 1:m, 1:n) where [l, m, n] = size (v). The output fv can be used directly as input to the patch function.

If called with additional input arguments x, y, and z that are three-dimensional arrays with the same size as v or vectors with lengths corresponding to the dimensions of v, then the volume data is taken at the specified points. If x, y, or z are empty, the grid corresponds to the indices (1:n) in the respective direction (see ‘meshgrid’).

The optional input argument col, which is a three-dimensional array of the same size as v, specifies coloring of the isosurface. The color data is interpolated, as necessary, to match isoval. The output structure array, in this case, has the additional field facevertexcdata.

If given the string input argument "noshare", vertices may be returned multiple times for different faces. The default behavior is to eliminate vertices shared by adjacent faces with unique which may be time consuming.

The string input argument "verbose" is supported for MATLAB compatibility, but has no effect.

Any string arguments must be passed after the other arguments.

If called with two or three output arguments, return the information about the faces f, vertices v, and color data c as separate arrays instead of a single structure array.

If called with no output argument, the isosurface geometry is directly plotted with the patch command and a light object is added to the axes if not yet present.

For example,

[x, y, z] = meshgrid (1:5, 1:5, 1:5);
v = rand (5, 5, 5);
isosurface (x, y, z, v, .5);

will directly draw a random isosurface geometry in a graphics window.

An example of an isosurface geometry with different additional coloring:

N = 15;    # Increase number of vertices in each direction
iso = .4;  # Change isovalue to .1 to display a sphere
lin = linspace (0, 2, N);
[x, y, z] = meshgrid (lin, lin, lin);
v = abs ((x-.5).^2 + (y-.5).^2 + (z-.5).^2);
figure ();

subplot (2,2,1); view (-38, 20);
[f, vert] = isosurface (x, y, z, v, iso);
p = patch ("Faces", f, "Vertices", vert, "EdgeColor", "none");
pbaspect ([1 1 1]);
isonormals (x, y, z, v, p)
set (p, "FaceColor", "green", "FaceLighting", "gouraud");
light ("Position", [1 1 5]);

subplot (2,2,2); view (-38, 20);
p = patch ("Faces", f, "Vertices", vert, "EdgeColor", "blue");
pbaspect ([1 1 1]);
isonormals (x, y, z, v, p)
set (p, "FaceColor", "none", "EdgeLighting", "gouraud");
light ("Position", [1 1 5]);

subplot (2,2,3); view (-38, 20);
[f, vert, c] = isosurface (x, y, z, v, iso, y);
p = patch ("Faces", f, "Vertices", vert, "FaceVertexCData", c, ...
           "FaceColor", "interp", "EdgeColor", "none");
pbaspect ([1 1 1]);
isonormals (x, y, z, v, p)
set (p, "FaceLighting", "gouraud");
light ("Position", [1 1 5]);

subplot (2,2,4); view (-38, 20);
p = patch ("Faces", f, "Vertices", vert, "FaceVertexCData", c, ...
           "FaceColor", "interp", "EdgeColor", "blue");
pbaspect ([1 1 1]);
isonormals (x, y, z, v, p)
set (p, "FaceLighting", "gouraud");
light ("Position", [1 1 5]);

See also: isonormals, isocolors, isocaps, smooth3, reducevolume, reducepatch, patch.

Demonstration 1

Demonstration 2

Demonstration 3

Package: octave