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Module category: Mapper



IsoSurface

The IsoSurface module creates an isosurface from a three dimensional structured or unstructured grid-based data set using the marching cubes algorithm. Optionally given data input can be mapped on the generated surface using interpolation. Each input port also accepts Sets of the appropriate types.

IsoSurface.png

IsoSurface has been tested on SGI, NEC SX4 and HP platforms.

Parameters

Name Type Description
gennormals Boolean Generation of surface normals. Since renderers often have problems generating normals on the fly, this option is recommended and TRUE by default.
genstrips Boolean Generation of triangle strips. This option can be used to take advantage of graphics hardware in the final rendering steps. Default is TRUE.
isopoint Vector Point determining the isosurface.
isovalue Boolean The isovalue to be extracted from the data set. The default value is 0.0.
autominmax Boolean -

Input Ports

Name Type Description
requiredmeshIn UniformGrid
RectilinearGrid
StructuredGrid
UnstructuredGrid
All kinds of grid-based data is accepted as input including sets.
requiredisoDataIn Float
Float
Scalar or vector data is accepted as input for isosurface generation. The number of elements (or vertices) must match that of the respective grid.
optionaldataIn Float
Float
Vec3
Vec3
This optional port can be used to map additional values onto the created isosurface for coloring.

Output Ports

Name Type Description
outputmeshOut Polygons
TriangleStrips
IsoSurface produced in either polygonal or optimized triangle strip format.
outputdataOut Float
Vec3
Interpolated data on the surface, when data has been provided at the optional input port dataIn.
outputnormalOut Unstructured_V3D_Normals Normals calculated based on the weighted average of the face normals of all neighbor faces of the resulting polygonal isosurface. Normal generation turned on results in a higher memory consumption of the isosurface module.

Examples

Figure: covise/net/general/examples/IsoSurface.net
isosurface_net.png

The first example network shows an isosurface generation using data from the GenDat module. The meshIn port of the IsoSurface module is connected to the meshOut port of the GenDat module. The isoDataIn is connected to the scalar data output port of GenDat. Only the meshOut port of the IsoSurface module has been connected to the Collect module in this example to test the normal generation feature of the Inventor renderer. It is recommended to use the normal output of the isosurface module in normal cases.

You find the map in the directory covise/net/general/examples.

The next image is a snapshot of the results in the Inventor Renderer.

renderer_snapshot.png

The next two images show a slightly more complicated example (IsoSurface2.net) and the corresponding renderer output.

Figure: covise/net/general/examples/IsoSurface2.net
isosurface2_net.png

renderer2_snapshot.png

Tunable Parameters

The IsoSurface module algorithm for unstructured grids has to allocate memory for the output vertices and the data interpolated on it. The size of this allocation is based on heuristics and by default set to 20% of the number of vertices in the input data set. However, this might not be enough for some data sets, especially if the Isosurface is extremely wrinkled.

In this case, the module terminates execution, submits a message, increases the ratio by 5% and re-executes itself. To prevent this procedure, establish a higher starting value by putting a section with a higher value (e.g. 50%) into your covise.config:

IsoSurface
{
   # Ratio of array size to number of input vertices in Percent
   VERTEX_RATIO   50
}

This value is used by both IsoSurface and IsoSurfaceP. The theoretical maximum value is 300% (VERTEX_RATIO 300).


Authors: Martin Aumüller, Ruth Lang, Daniela Rainer, Jürgen Schulze-Döbold, Andreas Werner, Peter Wolf, Uwe Wössner
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COVISE Version 2016.3