NotesME10E1

# NotesME10E1 - 3D Modeling Wire Frames are ambiguous...

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3D Modeling Wire Frames are ambiguous, depending on how faces are interpreted. Some Modelers approximate curved surfaces with a series of planar ones called facets. Using dimensional constraints can parameterize parts. A work plane It is used to support the creation of part geometry relative to the coordinate system and object. Construction geometry does not represent any of the final geometry representing the part, but instead provides a framework for guiding the construction of this part geometry. A Work plane can be used in the same manner as a drawing surface. In a modeler, work planes are typically used to orient the profile sketch used in feature generation. Many features on a part model begin as sketching a profile on a work plane. This sketch will consist of a series of line elements such as straight lines, arcs, circles, or splines. Existing features of the model, such as faces and individual vertices can be used to orient and allocate work planes. Objects can be sketched by using sweeping and Boolean operations. The assembly of parts into larger models uses many of the same techniques and concepts used in part modeling. In an assembly model, components are brought together to define a larger, more complex product representation. A component is either a part or another assembly brought into an assembly model and associated with other components. Each successive component brought in needs to be oriented and located relative to other components in the assembly. Location and orientation is achieved by defining geometric relations between geometric elements of a component in the assembly and the elements of component being brought in. Assemblies can contain single or multiple instances of components, subassemblies. Assembly models have associated hierarchical structures. A hierarchical structure allows parts to be grouped together logically into subassemblies. Some modelers also allow creation of mating constraints between component and subassembly instances. Having the component can automatically create an exploded view and subassembly instances move away form each other along the lines of the mating constraints applied in the assembly. The location and orientation of the instances can then be adjusted to create a more optimal view. Many modeling systems have a default view setup depicting the three standard multiviews and a pictorial view. The techniques used for viewing 3-D models are based on the principle of projection theory. The computer screen, like a sheet of paper, is 2-D. therefore, 3-D forms must be projected into 2-D. For review, the primary elements in creating a

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projection are the model (object), the viewer , and an image (view) plane. A related issue in view specification is how to display the geometry of the model.
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