D-Cubed CDM Product Tour (page 2 of 4)

Product Tour - Adding the Model to the CDM

The CDM uses a temporary representation of the application's model. Its internal model format is simple enough to be compatible with the model data-structures from just about any application. A CDM model can consist of any combination of application model formats, such as Parasolid®, ACIS® from Spatial and most proprietary vector geometry formats.

The application builds up the CDM's internal model using a simple sequence of function calls. Only the minimal model data that is necessary to perform a CDM computation is transferred, such as the geometric definition of the individual edges and faces in the application's modelling kernel. The application also informs the CDM about which edges form which faces and which faces form which parts. All types of geometry are supported, including lines, circles, ellipses, planes, cylinders, spheres, tori, cones, spline curves and surfaces, general parametric curves and surfaces, rolling ball surfaces and faceted surfaces.

The CDM supports the following types of data:

  • Solid, surface or wireframe
  • Manifold or non-manifold
  • Exact geometries (e.g. cylinders, tori and splines), or faceted approximations
  • Accurate or inaccurate models

The CDM uses the same model representation as the HLM and AEM. Integrating one component will be beneficial when integrating either of the other components.

Exact geometry or faceted geometry

We will now look at these stages in more detailA major strength of the CDM is that it has excellent performance with models that are represented by exact geometries, e.g. cylinders, tori and splines, rather than faceted approximations. Using exact geometries when they are available is essential for producing collision results that are of a high enough quality to support the engineering process. Those systems that can only use faceted data will miss some real collisions and report some false collisions-potentially expensive errors. The CDM does support faceted models if required, however, such as when this is the only representation available.

Inaccurate models

The issue of inaccurate models is significant when selecting a robust collision technology. Accurate models have a consistent connectivity between edges and faces and a high level of numerical precision in their geometric data. Inaccurate models can have a variety of characteristics, such as significant gaps between edges and their faces, gaps between adjacent faces, missing faces or other errors in model connectivity. These situations often arise in models that are imported from other applications. Inaccurate models, from whatever source, can cause serious problems in less robust systems than the CDM.

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