GeometricModeling ismathematicalrepresentationofthegeometryofanobjectusingsoftware.

GeometricModeling

Typesofgeometricmodelingmethods

y Wireframe modeling

y Surface modeling

y Solid modeling

Why Geometric modeling is needed

Geometric (3D) models are easier to interpret. Simulation under real-life conditions. Less expensive than building a physical model. 3D models can be used to perform finite

element analysis (stress, deflection, thermal) 3D models can be used directly in

manufacturing, Computer Numerical Control(CNC).

Can be used for presentations and marketing.

Wireframe Modeling

Wire-frame modelling uses points and curves (i.e. lines,circles, arcs) to define objects.

The user uses edges and vertices of the part to form a 3-Dobject

Wireframe model Part

Wireframe modeling - Advantages

Can quickly and efficiently convey information thanmulti view drawings. (orthographic view)

Can be used for finite element analysis.

Can be used as input for CNC machines to generatesimple parts.

Contain most of the information needed to createsurface, solid and higher order models

Tend to be not realistic

Do not represent an actual solids (no surface and

volume).

Cannot model complex curved surfaces.

Cannot be used to calculate dynamic properties.

Ambiguity complex model difficult to interpret.

Wireframe modeling - Disadvantages

Wireframe modeling - Disadvantages

Donotrepresentanactualsolids(nosurfaceandvolume).

Cannotmodelcomplexcurvedsurfaces. Cannotbeusedtocalculatedynamicproperties. Ambiguousviews

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Wireframe modeling - Disadvantages

Uniquenessproblem.

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A surface model represents the skin of an object, theseskins have no thickness or material type

y Surface modeling is more sophisticated than wireframemodeling in that it defines not only the edges of a 3D object,but also its surfaces.y In surface modeling, objects are defined by their bounding

faces.

2. Surface Modeling

Surface Entities Analytic entities include :

Plane surface, Ruled surface, Surface of revolution, and Tabulated cylinder.

Synthetic entities include Hermite Cubic spline surface, B-spline surface, Bezier surface, and Coons patches.

y Eliminates ambiguity and non-uniqueness present inwireframe models by hiding lines not seen.y Renders the model for better visualization and presentation,

objects appear more realistic.y Provides the surface geometry for CNC machining.y Provides the geometry needed for mold and die design.y Can be used to design and analyze complex free-formed

surfaces (car bodies)y Surface properties such as roughness, color and reflectivity

can be assigned and demonstrated.

Surface modeling - Advantages

Surface models provide no information about

the inside of an object.

Cannot be used to calculate dynamic

properties.

Surface modeling - Disadvantages

Plane surface

Ruled (lofted) surface. This is a linear surface. It interpolateslinearly between two boundary curves that define the surface.

Surface of revolution. This is an axisymmetric surface that canmodel axisymmetric objects. It is generated by rotating a planarwireframe entity in space about the axis of symmetry a certainangle.

Tabulated cylinder. This is a surface generated by translating aplanar curve a certain distance along a specified direction (axis ofthe cylinder).

Bezier surface. This is a surface that approximates given inputdata. It is different from the previous surfaces in that it is a syntheticsurface. Similarly to the Bezier curve, it does not pass through allgiven data points. It is a general surface that permits, twists, andkinks . The Bezier surface allows only global control of the surface.

Bspline surface. This is a surface that can approximate orinterpolate given input data. It is a synthetic surface. It is a generalsurface like the Bezier surface but with the advantage of permittinglocal control of the surface.

Geometric Modeling is mathematical representation of the geometry of an object using software.Types of geometric modeling methodsWhy Geometric modeling is neededWireframe ModelingWireframe modeling - AdvantagesWireframe modeling - DisadvantagesWireframe modeling - DisadvantagesWireframe modeling - Disadvantages2. Surface ModelingSurface Entities Surface modeling - AdvantagesSurface modeling - DisadvantagesSlide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18