



      VOLUME RENDERING DEMO


This program shows two separate visualizations
using IDL's volume rendering capabilities.

1.) "Dual Volume PET MRI" visulaization.  The Dual
Volume PET MRI visualization includes both
registered positron emission tomography (PET) and
magnetic resonance imaging (MRI) scans of a human
brain.  The demonstration modulates the values of
one of the scans by the values of the other scan.
The resolution of the PET and MRI brain data is 1mm
in the X, Y and Z dimensions.

The PET and MRI data sets were provided by Dr.
Hanna Damasio and Dr. Thomas Grabowski, Department
of Neurology, Division of Behavioral and Neurology
and Cognitive Neuroscience, University of Iowa
College of Medicine.

2.)  Electron Probability Density visualization.
The Electron Probability Density visualization is a
quantum mechanics calculation of a one-electron
orbital of a four-iron, eight-sulfur cluster found
in many natural proteins. The data is the squared
magnitude of the wave-function 'psi' at each
point.  This is the probability density of the
electron at that point.  The atoms are arranged in
a cube of alternating iron and sulfur atoms, with
sulfurs and methyl (CH3) groups on the iron
corners. This orbital, the highest occupied
molecular orbital [HOMO], has high intensity
joining two irons across a face diagonal.  It is
level 28a or level number 213.

The quantum mechanics data is from Louis Noodleman
and David Case, Scripps Clinic, La Jolla,
California.

MENU OPTIONS
------------

File Menu:

    Select "Quit" to exit the demo and return to the
    main IDL Demo screen.


Options Menu:

    Select "Wire box" to display (or hide) a
    rectangular box drawn around the rendered
    volume.

    Select "Solid plane" to display (or hide) a
    plane intersecting the rendered volume.

    Select "Axes lines" to display (or hide) three
    orthogonal lines, one red, one green, and one
    blue.  The lines intersect at the center of the
    volume.  The red line represents the X axis,
    green represents Y, and blue represents Z.

    Select "3D Cursor" to display (or hide) a set
    of orthogonal lines drawn through the rendered
    volume  The intersection of these lines can be
    moved by clicking the right mouse button on a
    rendered volume.  (If you only have one
    mouse-button, and you are on a Macintosh
    computer, hold down the Command key while
    pressing the mouse button to simulate a "right"
    mouse-button press.) The new intersection will
    be shown the next time a volume is rendered.

About Menu:

    Select "About volumes" to display this text.

CONTROL FEATURES OF THE VOLUME RENDERING DEMO
---------------------------------------------

<<Dual Volume PET MRI>> and 
<<Electron Potential Cloud>>  
    Click one of these buttons to select either a
    human brain or an electron probability cloud.

<<Render>> Button
    Click on this button to execute rendering
    computations and display the current volume.
    If "Auto-Render" is on, this button will be
    grayed out.

<<Auto-Render>> Button
    Select this option to have rendering executed
    automatically after each change you make to the
    volume or view.  If "Auto render" is off, you
    must manually click the "Render" button to see
    changes you have made to a volume or view.  If
    "Auto-Render" is on, the "Render" button will be
    grayed out.

<<Gradient Shading>> Button
    A light object (i.e. an IDLgrLight) is shining
    directional light (parallel rays) on the
    rendered volumes in this demonstration
    program.  To see the effect of this light,
    turn gradient shading on.  Local gradients
    (computed at each voxel in the current volume)
    will reflect the light.  When "Gradient Shading"
    is turned off, no effect from directional light
    can be seen.

    Note: Because normals must be computed for all
    voxels in a lighted view, enabling gradient
    shading increases the rendering time.

<<PET Colors>> or <<Colors>> Droplist Depending on
    which of the "Dual Volume PET MRI" and "Electron
    Probability Density" volumes you have selected,
    a "PET Colors" droplist or a "Colors" droplist
    will be visible.  Select from the current
    (visible) droplist to apply a color table to the
    current volume.

<<PET opacities>> or <<Opacities>> Depending on
    which of the two volumes, "Dual Volume PET MRI"
    and "Electron Probability Density", you have
    selected, a "PET Opacities" droplist or an
    "Opacities" droplist will be visible.  Select
    from the current (visible) droplist to apply an
    opacity table to the current volume.

<<Rendering Quality>> Radio buttons
    Select "medium (faster)" or "high" to effect the
    speed and accuracy of rendering.

<<Left Mouse-Button Action>>
    Select from this list of options to change how
    left-click-and-dragging in the graphic will
    change the view.  

<<Cutting Plane %>>
    Move the "Cutting Plane %" slider to cut away
    part of the volume in the volume's X dimension.
    The slider value shows a percentage of the
    distance from the current volume's front to the
    current volume's back.

Left-Click-and-dragging on the graphic.
    To change your view of the volume, position the
    mouse pointer in the graphics area, hold down
    the left mouse button, and drag the mouse.  The
    current Left Mouse-Button Action will be applied
    as you drag.  If you have the "Auto-Render"
    feature turned off, you will need to click the
    "Render" button to see the volume after you have
    changed your view.

    Tip: If you have the "rotate in screen Z" Left
    Mouse-Button Action selected, click and drag in
    a motion arcing about the center of the graphics
    area for consistent rotation speed.  The farther
    from the center you make your arc, the slower
    the rotation.

Right-clicking on the graphic.
    When the current volume is rendered, you can
    select voxels on the volume's exterior with the
    right mouse button.  (If you only have one
    mouse-button, and you are on a Macintosh
    computer, hold down the Command key while
    pressing the mouse button to simulate a "right"
    mouse-button press.) The x-position, y-position,
    z-position, and voxel value for the currently
    selected voxel are displayed in the lower right
    panel beneath the graphics area.

HOTKEYS:

    You can use your keyboard to select from the
    <<Left Mouse-Button Action>> menu.  To select
    one of the rotation constraints type:

       X, 
       Y,
       Z,
       R,
       G or
       B

    To select "Scale" from the <<Left Mouse-Button
    Action>> menu, type:

       S

    To select "Rotate Unconstrained"  from the <<Left
    Mouse-Button>> Action menu, type:

       U
