Chapter 2: 3D modeling

What is a solid model?

A complete, unique and unambiguous representation of an object. Consists of faces, edges, and vertices

What is geometric modeling?

The mathematical representation and visualization of the geometry of an idea within a digital system. It supports design analysis, drafting, production engineering, and I&QC

What are the Requicha and Voelecker requirements for geometric modeling?

-Model configuration is invariant to location and orientation

-Model has properly defined interior

-Has finite boundary conditions and can identify interior / exterior

-Is consistent under geometric operations

-Has finite mathematical representation

What are the three approaches to 3D modeling?

-Primitive approach

-Features approach

-Sketching Approach

Primitive modeling approach?

Uses primitives such as block, cone, cylinder, and toruses. Can be combined using oprations such as Boolean subtraction (Block - Cylinder = Block with a hole)

Feature modeling approach?

Similar to primitive, but replaces primitives with features and uses boolean operations (Ex: create a block feature > create a hole feature)

Sketching approach

Creates a 2 sketch / profile then uses operations to create a 3D model. Can be used for: extrusion, revolution, linear / nonlinear sweep, spirals

What are the three types of geometric models presented?

-2-1/2D geometric modeling (with extrusion and revolving geometry)

-3D geometric model

-Combination of the above 2

What three coordinate systems are there?

-Model Coordinate System (MCS)

-Working Coordinate System (WCS)

-Screen Coordinate System (SCS)

Model Coordinate System (MCS)

-The reference space of the model to which all model geometric data is stored.

-Default coordinate system for the software

Working Coordinate System (WCS)

-Auxiliary, user-defined coordinate system used when the desired plane/face is not one of the MCS orthogonal planes

-Facilitates geometric construction

-Requires 3 noncollinear points to define its XY plane

Screen Coordinate System (SCS)

-2D, device dependent coordinate system associate with graphics display

-Original usually at lower left corner of display

What is a sketch plane?

Geometry used as a reference plane for creating a sketch, considered a datum plane which is not part of the model itself

Parameters vs Dimensions: Parameters

Generalization of the sketch definition and create a template of the sketch

Parameters vs dimensions: Dimensions

Specifications of the sketch definitions and create a specific instance of it

What is a datum plane and why is it used?

A reference / construction plane used when a nonstandard construction plane is needed. It can be used for creating sketches, convenient hole placements, and dimensioning