ESM4714
Scientific Visual Data Analysis and Multimedia
Exercise #9: 3D & 4D Voxel Volume Visualization of Properties with 3D Gradients and 3D Gradients Changing with time.

NOTE: Highlighted italic text denotes user response.

Procedure:

1. Logon onto mercury -> pluto.smvc.vt.edu at the VT-CAVE classroom (SMVC).

2. Mount your optical disk (see procedure for mounting scsi devices).
3. Go to the ESM4714/examples directory.

4. Locate the PV-Wave procedure files for generating a rotating translucent volume.

   on your mounted optical disk:

   viz?% cd /optical/ESM4714/examples/brown/

   viz?% ls -la

   drwxr-xr-x  7 root          512 Feb 15  1995 .
   drwxr-xr-x 13 root          512 Feb 15  1995 ..
   -rw-r--r--  1 root          590 Feb 15  1995 List.brown
   -rwxr-xr-x  1 root        77225 Feb 15  1995 brown.ascii.start
   drwxr-xr-x  2 root          512 Feb 15  1995 make_ascii
   drwxr-xr-x  2 root          512 Feb 15  1995 make_bin
   drwxr-xr-x  2 root          512 Feb 15  1995 make_hdf
   drwxr-xr-x  2 root          512 Feb 15  1995 original_data
   drwxr-xr-x  4 root          512 Feb 15  1995 wave_procedures
   

5. Create a 3D voxel stereo spin image for the file pict250.file by replacing the file pict750.file in the procedure file m_spin.pro, and then view your result by executing the procedure file s_spin.pro.

   viz?% wave

   wave> m_spin (get and modify the file: m_spin750.pro)

   wave> s_spin (get and modify the file: s_spin750.pro )

   NOTE: You can temporarily stop the rotation by using the middle mouse button and resume rotation by pressing the right button or terminate the procedure all together with the left mouse button.

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   Images generated from these procedure files allow use to see the full three dimensional (3D) gradient of the density of gas to air mixing by using the voxel volume translucency. Often these 3D gradients can only be understood when viewing the volume by a smooth and continuous rotation. We point out that this rotating voxel image lacks the quantitative information format we require in most applications but none-the-less this method allows us to view the 3D gradients and hence the 3D structure. The effect of rotating voxel imaging in some cases yields dramatic results, especially when the function is continuous with several contrasting regions. Refer to Instabilities in Elliptical Jets for a more complete technical explanation.
   MPEG (365K)

   Fig. 1 Voxels show a continuous gas-air gradation but this three-dimensional structure can only be seen if rotated. This type of graphic is less quantitative and gives a more qualitative measure of the gradient of a scalar function where the independent variables are (x,y,z) coordinate space.

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6. Create your own head spin (224K mpeg) animation by modifying this existing procedure file by copying the file man_head.dat from the directory /optical/ESM4714/arl/examples. You can also download the man_head.dat file for the SciViz anonymous ftp site: ftp://ftp.sv.vt.edu/pub/MRI-Head/ man_head.dat . Note, that since the man_head.dat file is a binary file, you will need to specifiy the file dimensions (here we assume each pixel in 3D space is a one byte unsigned binary integer). You can find the original file dimensions (115,75,105) in the wave procedure file /optical/ESM4714/arl/examples/vol_ demo2.pro on the mounted optical disk. A more complete explanation on how this data set relates to 3D images in computer tomography is located at the Volume Visualization of Magnetic Resonance Imaging

7. A fourth independent variable, time, can be included in this method which will yield a 4D image. This is accomplished by viewing each 3D volume at an instant in time such that eash succesive time step is seen as the next volume. Another way to think of this is that a change in rotation, delta-theta corresponds to a change in time, delta-time. This was done for a stress wave launched from the bottom of a 3D cube of high anisotropic material. Using this technique allows the viewer to see the 3D wave bifrucation characteristic in highly anisotropic materials.

   This animation can be observed here by downloading the 3D-waves animation of plane waves propagating in Calcium Formation. A more complete explanation is give at the Simulation and Visualization of Energy Waves Propagating in 2-D and 3-D Anisotropic Media.