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3D Modeling Basics

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  1. 3D Modeling Basics Three basic types of 3D CAD models: • Wireframe models • Surface models • Solid models

  2. Wireframe Model • “wires” represent edges of the actual object. • surfaces of the object are not defined, only the boundaries of surfaces are represented by edges. • See-through; not useful for visualization • Has complete dimensional information but contains no volume. • Easy to construct • Created by constructing 2D objects (lines, circles, arcs, etc.) in 3D space. • Useful for planar or single-curved surfaces, but not compound curved surfaces. • Example: wireframe model of a cube is like a model constructed of 12 coat-hanger wires.

  3. Surface Model • Defines both surfaces and edges • Provides better visualization of the actual 3D object. • Requires relatively tedious construction process; each surface must be constructed and oriented with respect to other surfaces. • AutoCAD is not a complete surface modeler; only allows planar and single-curved surfaces. • Wireframe models are usually used as framework to build surfaces

  4. Solid Model • Most complete and descriptive type of 3D modeling. • A computerized replica of the actual object. • Contains definition of edges, surfaces, as well as the interior features of the object. • Has mass and volume; can calculate mass and volumetric properties • Construction techniques are usually simpler than those of surface modelers.

  5. Solid Modeling • AutoCAD’s solid modeler is called ACIS, which is a hybrid modeler. Combination of: • CSG (Constructive Solid Geometry) - a construction techniques that involves combining primitive shapes (boxes, cylinders, wedges, etc.), and utilizing Boolean operations (Union, Subtract, and Intersect) • B-Rep (Boundary Representation) - Defines a model in terms of its edges and surfaces (boundaries) and on which side of the surfaces the model lies. • SolidWorks – Parametric (or Feature-Based)

  6. Coordinate Systems • World Coordinate System (WCS) • Attached to the “ground” (“Real World”) • always available and cannot be erased • XY plane is horizontal, Z is the height dimension • User Coordinate System (UCS) • A temporary coordinate system created by user • Used to simplify the creation of geometry on a specific planes or surfaces of the object • Many ways of defining orientation and position

  7. 3D Coordinate Entry

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