WIREFRAME-MODEL

ENTITY GEOMETRIC MODEL = CLASS( WIREFRAME MODEL(DIM), 

The GEOMETRIC MODEL is a class representing entities according to the geometric modeling techniques WIREFRAME MODEL (two-dimensional and three-dimensional) SURFACE MODEL, and SOLID MODEL. 

WIREFRAME MODEL RESULT name list WIREFRAME MODEL ( name, CLOSE )  

A WIREFRAME MODEL is an entity that has a scope. A WIREFRAME MODEL may have a material property associated with it. Surface entities are required in wireframe models which contain geometry defined on surfaces (see Geometry on surfaces on page 93). The result is a list of references to bounded curves only. 

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Fig. 12.5. Crystal structures of (a) Ta and (b) Th along a-axis. Trehalose molecules are drawn by a spacefilling model with a partial wireframe model. There are two different holes in Ta hole 1 and hole 2. Diameter of each circle is 2.1 A. In Th, these holes are occupied by two crystal water molecules...

Figure 5. Structure of the [ 04(2)4] cation (wireframe model) showing the gridlike arrangement of the four ligands and the four metal ions (36).

Creating tolerances by use of constrained sections or wires in a wireframe model. Sections and wires are extracted from the geometric model representation of the part. 

Wire frames with unified topology and geometry use the same entities as solid models but without face and surface definitions. Note that these wire frames are not the same representations as the wire frames in the early era of geometric modeling. When a wireframe model defines a shape unambiguously, a surface or solid model can be replaced by the simple wire frame for economical modeling. If necessary, a verified wire frame can be completed into a surface or solid. 

Fig. 2.14 Schematic structure of the myoglobin of the sperm whale. The arrow indicates the wireframe model of heme with the attached oxygen molecule redballs), the blue ribbons represent the globin protein. (Authors own work and copyright-free Wikipedia picture)...

Of particular importance is the assumption of thin-walled geometry. From Eq. (7.3) we see that the pressure is independent of the z coordinate. Consequently, the finite element utilized for pressure calculation need have no thickness. That is, the element is a plane shell—generally a triangle or quadrilateral. This has great implications for users of plastics CAE. It means that a finite element model of the component is required that has no thickness. In the past this was not a problem. Almost all common CAD systems were using surface or wireframe modeling and thickness was never shown explicitly. The path from the CAD model to the FEA model was clear and direct. 

Plastics with their inherent complex geometries are typically better suited to boundary representation models. Also functions such as finite element modeling or numerical control tool paths require explicit surface definitions which are only available with boundary representations. With constructive solid geometry systems, surface information must be evaluated before it is user accessible. Wireframe models again may be used as the base and are easily transferred to a boundary representation system. Conversely a boundary representation model may be readily converted to a wireframe. Many current commercial systems combine the features of both constructive solid geometry and boundary representation. A project consisting of simple machineable shapes may be done faster in a constructive solid geometry mode while a sculptured surface model would be more easily created in a boundary representation mode. The separate models can... 

For example, three-dimensional wire-frame models can be constructed to help visualize the product and serve as a framework for other modeling programs. (More details on wire frame and other modeling techniques are presented later in this chapter.) These wireframe models, which are constructed in three dimensions, can normally be viewed in orthographic, isometric, or perspective views, often at the same time. Changing one view alters all the other ones. Wire frames are easily modified, and many design variations can be constructed in a relatively short time. 

The wireframe model is a skeletal description of a 3-D part. It consists only of points, lines, and curves that describe the geometric boundaries of the object. There are no surfaces in a wireframe model. The 3-D wireframe representations can be confusing because all of the lines defining the object appear on the 2-D display screen. This makes it difficult for the viewer to tell whether the model is being viewed from above or below, inside or outside. It is the simplest of the CAD/CAM modeling methods. The simplicity of this modeling method also implies simplicity in the database. 

Asn-51 (gray) and Met-54 (green). The DNA is shown as a wireframe model. Positions of interfacial water molecules are given by dark blue spheres. After Reference [204]. 

For two-dimensional wireframe models a set of straight lines and an associated point set for each line is transmitted. For each transfer line the associated point set represents the intersection points of the line with the wireframe model. 

For three-dimensional wireframe models intersection points between the curves of the model and test planes are to be used. 

Solid models, surface models, and wireframe models... 

This entity type represents all bounded curves. It consists of the trimmed curves and those conics that are bounded by their geometric definition. The purpose of introducing this entity type is to guarantee that the result of a wireframe model is always bounded. 

The surface curve is a single scoped entity which contains in its scope the complete data structure that defines the curve geometry, hence, in wireframe models the surface-curve behaves as a single three-dimensional curve entity (see "Points and curves" on page 56 and "Geometry on surfaces"). The curve attribute refers to the top of that data structure. The surface entities which are referred from within the curve on surface entities may lie within the scope of the same surface-curve or outside. 

This relation expresses the fact that the points referenced by the results attribute have been produced in the sending CAD system by intersecting the two-dimensional wireframe model referenced by the geometry attribute with the test line. The CAD system user in the receiving environment may use this information to test the accuracy of the transmitted geometry by repeating this intersection operation. 

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