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Chapter 9: Visualization and GraphicsSection 9.1 – Why Study Visualization and Graphics?

Visualization and Graphical communication skills are important to many engineering disciplines

Some engineering disciplines no longer require drafting classes of any type

The prevalence of computers in the workplace has increased the need for visualization and graphical communication skills

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Chapter 9: Visualization and GraphicsSection 9.2 – The Theory of Projection

A method is necessary to depict 3D objects on 2D media like drawings and computer screens

Orthographic Projection incorporates a series of 2D views of an object, yet still completely defines the object

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Chapter 9: Visualization and GraphicsSection 9.2 – The Theory of Projection

Projection Theory involves 4 specific components:

1. An object2. An observer3. A projection plane (or picture

plane)4. Visual rays

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Chapter 9: Visualization and GraphicsSection 9.2 – The Theory of Projection

When the visual rays converge, the projection onto a plane represents a perspective drawing

When the visual rays are parallel (i.e., the observer is very distant), the projection onto a plane represents orthographic projection

The prefix ortho- means perpendicular

Orthographic projection represents views of an object that are all oriented so that the visual rays are perpendicular to the object

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Chapter 9: Visualization and GraphicsSection 9.3 – The Glass Box Theory

Suspending an object in a Glass Box, and viewing that object through different faces of that box, is the basis for orthographic projection.

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Chapter 9: Visualization and GraphicsSection 9.3 – The Glass Box Theory

If an object’s 3 dimensions are labeled as (1) height, (2) width, and (3) depth, every orthographic view will show exactly 2 of those 3 dimensions:

The front view shows Height and Width only

The right side view shows Height and Depth only

The top view shows Width and Depth only

width

height

depth

depth

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Chapter 9: Visualization and GraphicsSection 9.4 – First and Third Angle Projections

The method for how to show and align the different 2D orthographic views leads to 2 main types of projections:

First Angle Projection (used in Europe) Third Angle Projection (used in the U.S.)

Third Angle Projection shown here is used predominantly in the U.S.

Third Angle Projection

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Chapter 9: Visualization and GraphicsSection 9.5 – The Meaning of Lines

Lines used in orthographic projection can have various meanings, including:

Representing an edge of planar surface The intersection of two surfaces The limiting element of a curved

surface In orthographic projection, there are only 3 different ways to depict any planar surface:

As an edge (i.e., in Edge View, or EV) As a true-size surface, where the line of

sight is perpendicular to that surface (i.e., True Size, or TS)

As a foreshortened surface

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Chapter 9: Visualization and GraphicsSection 9.6 – Hidden Lines

Orthographic views show all features of an object, including those hidden in a particular view

Hidden lines are drawn as dashed lines

Hidden lines represent features of an object which are hidden in that particular orthographic view

Hidden lines are drawn with a thinner line weight, in addition to being dashed, to distinguish them from thicker, continuous lines used for Visible lines.

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Chapter 9: Visualization and GraphicsSection 9.6 – Hidden Lines

Orthographic views show all features of an object, including those hidden in a particular view

Hidden lines are drawn as dashed lines

Hidden lines represent features of an object which are hidden in that particular orthographic view

Hidden lines are drawn with a thinner line weight, in addition to being dashed, to distinguish them from thicker, continuous lines used for Visible lines.

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Chapter 9: Visualization and GraphicsSection 9.7 – Cylindrical Features and Radii

Cylindrical features are considered either:

Positive e.g., Outside surface of cylinder

Negative e.g., Holes with circular cross-sections

Centerlines are viewed differently in different orthographic views of a cylinder:

When viewing the circle true size, the center line looks like a cross hair (+)

When viewing the cylinder longitudinally, the center line looks like a single line with a break in the middle

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Chapter 9: Visualization and GraphicsSection 9.8 – The Alphabet of Lines and Line Precedence Line Precedence

Visible lines have highest precedence

Hidden lines have 2nd highest precedence; if visible and hidden lines coincide, only the visible lines are shown

Center lines have 3rd highest precedence

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Chapter 9: Visualization and GraphicsSection 9.9 – Freehand Sketching

Freehand sketching is very important to the engineer

Quick graphical representations are used frequently to communicate with a variety of others

Proportions are important in freehand sketching

Sketching curved lines represents the greatest challenge in freehand sketching

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Chapter 9: Visualization and GraphicsSection 9.10 – Pictorial Sketching

Pictorial sketching: creating a view of the object in which all 3 dimensions are shown

3 Types of Pictorial Sketches:

1. Axonometric (including isometric)2. Oblique3. Perspective

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Chapter 9: Visualization and GraphicsSection 9.10 – Pictorial Sketching

Isometric Sketches: all 3 dimensions are drawn parallel to each other

Oblique Sketches: The width and height dimensions are drawn perpendicular to each other; the depth dimension is drawn receding at some angle. Depth dimensions are parallel.

Perspective Sketches: At least one dimension has lines which converge on a vanishing point. This is the most realistic looking of all pictorial sketches, yet typically the most time consuming.

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Chapter 9: Visualization and GraphicsSection 9.11 – Visualization

Three Types of Surfaces are used to create a three-dimensional object:

1. Principal surfaces2. Inclined surfaces3. Oblique surfaces

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Chapter 9: Visualization and GraphicsSection 9.12 – Scales and Measuring

A Scaled Drawing means that there is a constant ratio between the length of a feature on a drawing, and the true length of what it represents

A Scale can represent both (a) a numeric ratio and (b) the tool used to draw and measure features.

Types of scales include: Engineer’s Scale Architect’s Scale Metric Scale

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Chapter 9: Visualization and GraphicsSection 9.13 – Coordinate Systems and 3D Space Computer-Aided-Drafting, or

CAD, has been common prevalent in many areas of engineering

2D CAD drawings rely on knowledge of x-y Cartesian coordinate systems

3D CAD drawings rely on knowledge of x-y-z coordinate systems