Volume Visualization Techniques (Using MATLAB Graphics)

Using MATLAB Graphics

Connecting Equal Values with Isosurfaces

Isosurfaces are constructed by creating a surface within the volume that has the same value at each vertex. Isosurface plots are similar to a contour plots in that they both indicate where values are equal.

Isosurfaces are useful to determine where in a volume a certain threshold value is reached or to observe the spacial distribution of data by selecting various isovalues at which to generating a plot. The isovalue must lie within the range of the volume data.

Create isosurfaces with the isosurface and patch commands.

Example - Isosurfaces in Fluid Flow Data

This example creates isosurfaces in a volume generated by the flow M-file. Generate the volume data with the command,

[x,y,z,v] = flow;

To select the isovalue, determine the range of values in the volume data.

min(v(:))
ans =
    -11.5417
max(v(:))
ans =
    2.4832

Through exploration, you can select isovalues that reveal useful information about the data. Once selected, use the isovalue to create the isosurface:

Use isosurface to generate data that you can pass directly to patch.
Recalculate the surface normals from the gradient of the volume data to produce better lighting characteristics (isonormals).
Set the patch FaceColor to red and the EdgeColor to none to produce a smoothly lit surface.

Adjust the view and add lighting (daspect, view, camlight, lighting).

hpatch = patch(isosurface(x,y,z,v,0));
isonormals(x,y,z,v,hpatch)
set(hpatch,'FaceColor','red','EdgeColor','none')
daspect([1,4,4])
view([-65,20])
axis tight
camlight left; lighting phong

[ Previous | Help Desk | Next ]