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isosurface

Extract isosurface data from volume data

Syntax

fv = isosurface(X,Y,Z,V,isovalue)
fv = isosurface(V,isovalue)
fvc = isosurface(...,colors)
fv = isosurface(...,'noshare')
fv = isosurface(...,'verbose')
[f,v] = isosurface(...)
[f,v,c] = isosurface(...)
isosurface(...)

Description

fv = isosurface(X,Y,Z,V,isovalue) computes isosurface data from the volume data V at the isosurface value specified in isovalue. That is, the isosurface connects points that have the specified value much the way contour lines connect points of equal elevation.

The arrays X, Y, and Z represent a Cartesian, axis-aligned grid. V contains the corresponding values at these grid points. The coordinate arrays (X, Y, and Z) must be monotonic and conform to the format produced by meshgrid. V must be a 3D volume array of the same size as X, Y, and Z.

The struct fv contains the faces and vertices of the isosurface, which you can pass directly to the patch command.

fv = isosurface(V,isovalue) assumes the arrays X, Y, and Z are defined as [X,Y,Z] = meshgrid(1:n,1:m,1:p) where [m,n,p] = size(V).

fvc = isosurface(...,colors) interpolates the array colors onto the scalar field and returns the interpolated values in the facevertexcdata field of the fvc structure. The size of the colors array must be the same as V. The colors argument enables you to control the color mapping of the isosurface with data different from that used to calculate the isosurface (e.g., temperature data superimposed on a wind current isosurface).

fv = isosurface(...,'noshare') does not create shared vertices. This is faster, but produces a larger set of vertices.

fv = isosurface(...,'verbose') prints progress messages to the command window as the computation progresses.

[f,v] = isosurface(...) or [f,v,c] = isosurface(...) returns the faces and vertices (and faceVertexcCData) in separate arrays instead of a struct.

isosurface(...) with no output arguments, creates a patch in the current axes with the computed faces and vertices. If no current axes exists, a new axes is created with a 3-D view and appropriate lighting.

Special Case Behavior — isosurface Called with No Output Arguments

If there is no current axes and you call isosurface with without assigning output arguments, MATLAB® creates a new axes, sets it to a 3-D view, and adds lighting to the isosurface graph.

Examples

Example 1

This example uses the flow data set, which represents the speed profile of a submerged jet within an infinite tank (type help flow for more information). The isosurface is drawn at the data value of -3. The statements that follow the patch command prepare the isosurface for lighting by

  • Recalculating the isosurface normals based on the volume data (isonormals)

  • Setting the face and edge color (set, FaceColor, EdgeColor)

  • Specifying the view (daspect, view)

  • Adding lights (camlight, lighting)

    [x,y,z,v] = flow;
    p = patch(isosurface(x,y,z,v,-3));
    isonormals(x,y,z,v,p)
    set(p,'FaceColor','red','EdgeColor','none');
    daspect([1,1,1])
    view(3); axis tight
    camlight 
    lighting gouraud

Example 2

Visualize the same flow data as above, but color-code the surface to indicate magnitude along the X-axis. Use a sixth argument to isosurface, which provides a means to overlay another data set by coloring the resulting isosurface. The colors variable is a vector containing a scalar value for each vertex in the isosurface, to be portrayed with the current color map. In this case, it is one of the variables that define the surface, but it could be entirely independent. You can apply a different color scheme by changing the current figure color map.

[x,y,z,v] = flow; 
[faces,verts,colors] = isosurface(x,y,z,v,-3,x); 
patch('Vertices', verts, 'Faces', faces, ... 
    'FaceVertexCData', colors, ... 
    'FaceColor','interp', ... 
    'edgecolor', 'interp');
view(30,-15);
axis vis3d;
colormap copper

More About

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Tips

You can pass the fv structure created by isosurface directly to the patch command, but you cannot pass the individual faces and vertices arrays (f, v) to patch without specifying property names. For example,

patch(isosurface(X,Y,Z,V,isovalue))

or

[f,v] = isosurface(X,Y,Z,V,isovalue);
patch('Faces',f,'Vertices',v)

See Also

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