General Concepts in 3D Modeling and Techniques - chp4

solid model

A 3D digital geometric representation of an object, consisting of volumetric information.

manifold model in 3D modeling

A model where the boundary separates the inside from the outside unambiguously.

geometric primitives in 3D modeling

Basic shapes such as cubes, prisms, spheres, cones, and cylinders.

primitive instancing

Using a set of predefined geometric primitives to construct more complex objects.

constructive solid geometry (CSG)

A modeling technique that combines primitives using Boolean operations.

types of Boolean operations

Union (∪), difference (−), and intersection (∩).

result of a union Boolean operation

The two primitives are combined, and the overlapping volume is represented only once.

difference Boolean operation

It subtracts one shape from another, leaving only the non-overlapping parts.

intersection Boolean operation

It keeps only the area of overlap between two primitives and removes the rest.

B-rep (boundary representation) model

A modeling technique where surfaces are used to define solids, representing inside and outside.

constraint-based modeling

A technique where the model is defined through modifiable constraints and features.

associativity in constraint-based modeling

The ability of a model to update related features automatically when one feature is modified.

importance of planning in constraint-based modeling

To ensure that the model can be easily modified and used for various purposes.

types of data sources in constraint-based modeling

Rough sketches, 2D CAD drawings, and models reused from the same system.

3D model for analysis

By ensuring critical features are modeled with enough detail for finite element analysis (FEA).

considerations when planning a 3D model

The final geometry, level of detail, and how modifications will be automated.

feature order in constraint-based modeling

It influences how features interact and how easily the model can be modified.

purpose of standards in modeling

To ensure models are easier to modify and can be used by others.

feature duplication in 3D modeling

Copying or mirroring features to create symmetrical or repetitive elements.

design constraints effect on model behavior

Constraints automatically adjust related features to maintain design intent.

face-to-face rule in combining solids

A flat face of one object must join a flat face of another for a true combination.

negative solid

A solid removed from another to create a void that perfectly matches the removed part.

additive and subtractive techniques in solid modeling

Additive techniques add objects together; subtractive techniques remove one object from another.

development in solid modeling

Flattening the surfaces of a solid object to see all its faces at once.

difference between single-curved and double-curved surfaces

Single-curved surfaces curve in one dimension, while double-curved surfaces curve in two.

linear sweeping in 3D modeling

Moving a 2D profile along a straight path to create a 3D feature.

revolved sweeping

Moving a 2D profile around an axis to create a circular 3D feature.

blend sweeping (lofting)

Creating a feature by moving a profile along multiple paths or shapes.

path-based sweep

Moving a profile along a predefined path, creating a more complex feature.

sketch plane in 3D modeling

A plane used as the basis for drawing a profile that will be swept or extruded.

construction geometry

Geometry that provides a framework for feature creation but is not part of the final model.

blind sweep in feature creation

A sweep that has a finite distance, as opposed to an infinite or 'through all' sweep.

through-next sweep

A sweep that stops when it hits the next feature or surface in the model.

open loop profile

A profile that doesn't form a closed shape but can be used to create thin features.

wireframe views

A visualization method that displays only the edges of the model, without surfaces.

'hidden lines removed'

A view where lines behind solid surfaces are not shown.

shaded views in 3D modeling

Views where surfaces are filled with color or shading to provide a more realistic visualization.

near-isometric view

A view that shows three dimensions but is not fully isometric, often used to emphasize specific features.

tangency in 3D modeling

The point where two surfaces or curves touch without crossing.

simplified representations of a 3D model

Lower-detail versions of a model used for faster rendering or analysis.

Normal face

A face perpendicular to the viewing plane or surface.

Cutting plane

A 2D surface used to slice through a model to create a cross-section.

Symmetry

A condition where one half of an object is identical to the other half.

Feature order

Changing the sequence of feature creation can alter the final shape and behavior of the model.

User's viewpoint

The user's viewpoint determines how the model is viewed and can reveal hidden or distorted features.

Geometric decompositions

Breaking down a complex model into simpler geometric elements for easier construction.

Linear sweep

Moving a 2D profile along a straight path to create a 3D feature.

Revolved sweep

A profile is revolved around an axis to create a circular or cylindrical 3D feature.

Blend sweep (loft)

A method where multiple cross-sectional profiles are connected, creating smooth transitions between shapes.

Path-based sweep

A profile is swept along a specific path to create more complex shapes, such as curves.

Sketch plane

A reference plane used to draw a 2D profile that can be swept, extruded, or revolved.

Construction geometry

Geometry that provides structure and guidance for feature creation but is not part of the final model.

Blind sweep

A sweep that moves a profile a specified distance without passing through other geometry.

Infinite sweep

A sweep that extends infinitely through all other features in the model.

Through-next sweep

A sweep that stops when it encounters the next internal feature or boundary.

Open loop profile

A profile that does not form a closed shape, often used for thin features or surfaces.

Feature duplication

The process of copying or mirroring features to replicate elements in the design.

Symmetry in CAD modeling

Symmetrical objects are mirrored so that one half is identical to the other, simplifying design.

Face-to-face rule

For solids to combine properly, a flat face of one object must be joined to a flat face of another.

Negative solid modeling

Removing one solid from another, creating a void that matches the shape of the removed part.

Datum plane

A reference plane used for constructing and orienting features relative to the model's coordinate system.

Methods for specifying a sketch plane

Through, offset/parallel, angle, point or edge, and tangent.

Purpose of construction geometry

It acts as a guide for locating and orienting features but does not appear in the final model.

World coordinate system

It provides the global reference for all geometric elements and construction in a 3D space.

Precision when sketching a profile

By using construction lines, selecting a normal view of the sketch plane, and applying constraints.

Advantages of switching between multiple views

It helps visualize the sketch in relation to other geometry and ensures accuracy in complex profiles.

Thin feature

A feature with an open loop profile that creates a thin wall or sheet-like surface.

Distance for a sweep

By specifying the sweep distance as either finite (blind), infinite (through-all), or through-next.

Importance of feature planning

It ensures that features are created in a logical order, avoiding conflicts and facilitating future edits.

Common ways to view a 3D model

Wireframe, hidden lines removed, hidden lines rendered, and shaded views.

Normal face view

To provide a precise, perpendicular view of a face for accurate feature creation and analysis.

Tangency line

A line that indicates where two surfaces touch without crossing each other.

Isometric view

A 3D view where all three primary dimensions are equally visible, often used for overall visualization.

Simplified representations of a model

By reducing the number of details, such as using fewer polygons or approximating curved surfaces with flat ones.

User's role in viewing a model in CAD

The user manipulates the viewpoint, rotating or zooming to inspect different features of the model.

Camera strategies for viewing a 3D model

Choose views that clearly show important features, avoid distorted views, and use multiple viewports when necessary.