Visualizing Volume Data

This example shows several methods for visualizing volume data in MATLAB®.

Display Isosurface

An isosurface is a surface where all the points within a volume of space have a constant value. Use the isosurface function to generate the faces and vertices for the outside of the surface and the isocaps function to generate the faces and vertices for the end caps of the volume. Use the patch command to draw the volume and its end caps.

load mri D                                     % load data
D = squeeze(D);                                % remove singleton dimension
limits = [NaN NaN NaN NaN NaN 10];
[x, y, z, D] = subvolume(D, limits);           % extract a subset of the volume data

[fo,vo] = isosurface(x,y,z,D,5);               % isosurface for the outside of the volume
[fe,ve,ce] = isocaps(x,y,z,D,5);               % isocaps for the end caps of the volume

figure
p1 = patch('Faces', fo, 'Vertices', vo);       % draw the outside of the volume
p1.FaceColor = 'red';
p1.EdgeColor = 'none';

p2 = patch('Faces', fe, 'Vertices', ve, ...    % draw the end caps of the volume
   'FaceVertexCData', ce);
p2.FaceColor = 'interp';
p2.EdgeColor = 'none';

view(-40,24)
daspect([1 1 0.3])                             % set the axes aspect ratio
colormap(gray(100))
box on

camlight(40,40)                                % create two lights 
camlight(-20,-10)
lighting gouraud

Create Cone Plot

The coneplot command plots velocity vectors as cones at x, y, z points in a volume. The cones represent the magnitude and direction of the vector field at each point.

cla                                            % clear the current axes
load wind u v w x y z                          % load data 

[m,n,p] = size(u);
[Cx, Cy, Cz] = meshgrid(1:4:m,1:4:n,1:4:p);    % calculate the location of the cones

h = coneplot(u,v,w,Cx,Cy,Cz,y,4);              % draw the cone plot
set(h,'EdgeColor', 'none')

axis tight equal
view(37,32)
box on
colormap(hsv)
light

Plot Streamlines

The streamline function plots streamlines for a velocity vector at x, y, z points in a volume to illustrate the flow of a 3-D vector field.

cla

[m,n,p] = size(u);
[Sx, Sy, Sz] = meshgrid(1,1:5:n,1:5:p);    % calculate the starting points of the streamlines

streamline(u,v,w,Sx,Sy,Sz)                 % draw the streamlines

axis tight equal
view(37,32)
box on

Plot Streamtubes

The streamtube function plots streamtubes for a velocity vector at x, y, z points in a volume. The width of the tube is proportional to the normalized divergence of the vector field at each point.

cla

[m,n,p] = size(u);
[Sx, Sy, Sz] = meshgrid(1,1:5:n,1:5:p);    % calculate the starting points of the streamlines

h = streamtube(u,v,w,Sx,Sy,Sz);            % draw the streamtubes and return an array of surfaces
set(h, 'FaceColor', 'cyan')                % use 'set' to change properties for an array of objects
set(h, 'EdgeColor', 'none')

axis tight equal
view(37,32)
box on
light

Combine Volume Visualizations

Combine volume visualization in a single plot to get a more comprehensive picture of a velocity field within a volume.

cla
spd = sqrt(u.*u + v.*v + w.*w);                          % wind speed at each point in the volume

[fo,vo] = isosurface(x,y,z,spd,40);                      % isosurface for the outside of the volume
[fe,ve,ce] = isocaps(x,y,z,spd,40);                      % isocaps for the end caps of the volume

p1 = patch('Faces', fo, 'Vertices', vo);                 % draw the isosurface for the volume
p1.FaceColor = 'red';
p1.EdgeColor = 'none';

p2 = patch('Faces', fe, 'Vertices', ve, ...              % draw the end caps of the volume
   'FaceVertexCData', ce);
p2.FaceColor = 'interp';
p2.EdgeColor = 'none' ;

[fc, vc] = isosurface(x, y, z, spd, 30);                 % isosurface for the cones
[fc, vc] = reducepatch(fc, vc, 0.2);                     % reduce the number of faces and vertices
h1 = coneplot(x,y,z,u,v,w,vc(:,1),vc(:,2),vc(:,3),3);    % draw the coneplot
h1.FaceColor = 'cyan';
h1.EdgeColor = 'none';

[sx, sy, sz] = meshgrid(80, 20:10:50, 0:5:15);           % starting points for streamline
h2 = streamline(x,y,z,u,v,w,sx,sy,sz);                   % draw the streamlines
set(h2, 'Color', [.4 1 .4])

axis tight equal
view(37,32)
box on
light

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