Viewing Isosurfaces Within a Resampled Volume

Volume rendering in Simcenter STAR-CCM+ is based on a ray-casting approach that is implemented in graphics hardware. The isosurface volume rendering mode tries to capture user-defined isovalues of interest during ray-casting through the resampled volume derived part.

The Isosurface Mode node allows you to choose between single and multiple surfaces for volume rendering in its properties.

Isosurfaces: the Volume Rendering Mode Compared with the Derived Part

Volume rendered isosurfaces are in principle similar to isosurface derived parts. However, volume rendered isosurfaces provide a better visual accumulation of partly transparent surfaces than isosurface derived parts with the same opacity settings. The data inputs, data extraction approaches, and storage locations of these types of objects are different. The effects of the inputs and extraction depend on the mesh, the native data location of the scalar field, and the accuracy settings for the resampled volume part.



Volume Rendered Isosurfaces	Isosurface Derived Parts


Isosurface Approach	Data Input	Extraction Approach	Hardware Employed	Storage	Location
Volume Rendering Mode	Resampled Volume derived part	Ray-Casting	Graphics Hardware / GPU	Image buffer in graphics memory	Client
Derived Part	Discrete meshed region or part	Polygonalization of intersected mesh edges	CPU	Polygonal surface mesh in main memory	Client and Server

For an interactive exploration of simulation results, volume rendered isosurfaces have the following advantages over isosurface derived parts:

Typically they update very fast, at the speed of volume rendering.
They provide better results that are based on the opacity that you specify in the displayer and the color maps.

In comparison to the derived parts, volume rendered isosurfaces have the following limitations:

They cannot show a secondary scalar field on their surface.
They cannot serve as an input to other derived parts or reports.
They support a maximum of 32 isovalues.
Their accuracy depends on the resolution of the underlying resampled volume. An example is bumpy disruptions of an otherwise flat surface. If such artifacts occur, use isosurface derived parts.

Specifying Volume Rendered Isosurfaces

To work with a single volume rendered isosurface, in the scalar displayer that contains the resampled volume, select the Resampled Volume Settings > Isosurface Mode > Value node and enter a value for Isovalue.
To work with multiple volume rendered isosurfaces that are equally spaced in a range:
- Select the Resampled Volume Settings > Isosurface Mode node and set Isosurface Mode to Multiple (range).
- Select the Isosurface Mode > Values (Range) node and set the following properties:
  - Number of Isosurfaces
  - Isovalue Range
For more information on the available properties, see Volume Rendered Isosurface Mode Properties .
To work with multiple volume rendered isosurfaces that you arbitrarily set:
- Select the Isosurface Mode node and set Isosurface Mode to Multiple (arbitrary).
- Select the Isosurface Mode > Values (arbitrary) node and set the properties using one of the following techniques:
  - Enter settings for Isovalues.
  - Click (Property Customizer) of the Isovalues property.
    
    In the dialog that appears, enter values as follows:
    - Set the number of volume rendered isosurfaces in the spin box.
    - If you know the exact values to display, enter them manually in the text box and click OK.
    - If you want Simcenter STAR-CCM+ to generate values, click Query, then click Auto Generate Values. Click OK.
      
      The Query action retrieves the scalar range from the server. The Auto Generate Values action produces an even set of values in the text box according to the number of volume rendered isosurfaces that you specify.

Examples of Effects of Volume Rendering Settings on Volume Rendered Isosurfaces

Lighting mode:



Local lighting on


Local lighting off

Opacity:



Displayer Opacity = 0.05


Displayer Opacity = 0.75