Exploring Volumes with Slice Planes
Slicing Fluid Flow Data
A slice plane (which does not have to be planar) is a surface that takes on
coloring based on the values of the volume data in the region where the slice is
positioned. Slice planes are useful for probing volume data sets to discover where
interesting regions exist, which you can then visualize with other types of graphs
slice example). Slice planes are
also useful for adding a visual context to the bound of the volume when other
graphing methods are also used (see
coneplot and Display Streamlines Using Vector Data for
slice function to create slice
planes. This example slices through a volume generated by
1. Investigate the Data
Generate the volume data with the command:
[x,y,z,v] = flow;
Determine the range of the volume by finding the minimum and maximum of the coordinate data.
xmin = min(x(:)); ymin = min(y(:)); zmin = min(z(:)); xmax = max(x(:)); ymax = max(y(:)); zmax = max(z(:));
2. Slice Plane at an Angle to the X-Axes
To create a slice plane that does not lie in an axes plane, first define a surface and rotate it to the desired orientation. This example uses a surface that has the same x- and y-coordinates as the volume.
hslice = surf(linspace(xmin,xmax,100),... linspace(ymin,ymax,100),... zeros(100));
Rotate the surface by -45 degrees about the x-axis and
save the surface
ZData to define the slice
plane; then delete the surface.
rotate(hslice,[-1,0,0],-45) xd = get(hslice,'XData'); yd = get(hslice,'YData'); zd = get(hslice,'ZData');
3. Draw the Slice Planes
Draw the rotated slice plane, setting the
interp so that it is colored by the figure colormap, and
none. Increase the
.8 to make this plane
shine more brightly after adding a light source.
colormap(turbo) h = slice(x,y,z,v,xd,yd,zd); h.FaceColor = 'interp'; h.EdgeColor = 'none'; h.DiffuseStrength = 0.8;
and add three more orthogonal slice planes at
zmin to provide a context
for the first plane, which slices through the volume at an angle.
hold on hx = slice(x,y,z,v,xmax,,); hx.FaceColor = 'interp'; hx.EdgeColor = 'none'; hy = slice(x,y,z,v,,ymax,); hy.FaceColor = 'interp'; hy.EdgeColor = 'none'; hz = slice(x,y,z,v,,,zmin); hz.FaceColor = 'interp'; hz.EdgeColor = 'none';
4. Define the View
To display the volume in correct proportions, set the data aspect ratio to
daspect). Adjust the axis to
fit tightly around the volume (
axis). The orientation of the
axes can be selected initially using
rotate3d to determine the best
Zooming in on the scene provides a larger view of the volume (
camzoom). Selecting a
projection type of
perspective gives the rectangular solid
more natural proportions than the default orthographic projection (
daspect([1,1,1]) axis tight view(-38.5,16) camzoom(1.4) camproj perspective
5. Add Lighting and Specify Colors
Adding a light to the scene makes the boundaries between the four slice planes
more obvious because each plane forms a different angle with the light source
lightangle). Selecting a
colormap with only 24 colors (the default is 64) creates visible gradations that
help indicate the variation within the volume.
Modify the Color Mapping shows how to modify how the data is mapped to color.
Modify the Color Mapping
The current colormap determines the coloring of the slice planes. This enables you to change the slice plane coloring by:
Changing the colormap
Changing the mapping of data value to color
Suppose, for example, you are interested in data values only between -5 and 2.5
and would like to use a colormap that mapped lower values to reds and higher values
to blues (that is, the opposite of the default
1. Customize the Colormap
Flip the colormap using
2. Adjust the Color Limits
Adjust the color limits to emphasize any particular data range of interest. Adjust the color limits to range from -5 to 2.4832 to map any value lower than the value -5 (the original data ranged from -11.5417 to 2.4832) into the same color.
Before R2022a: Adjust the color limits using
caxis, which has the same syntaxes and arguments as
3. Add a Color Bar
Add a color bar to provide a key for the data-to-color mapping.