# Notes can be found as interactive webpage at

7-9: Visualization

# Orthographic projections #

## Formal (working) drawings: purpose #

• Need a formal way of documenting designs
• Legal documents i.e patents; contracts may rely on them
• Must stand on their own – readable to any human
• No subsequent explanation
• No verbal assists
• No ambiguity
• Solution: multi-view orthographic projection
• World-wide engineering standard
• Can easily include tolerances

## What is a projection? #

Projection of a 3D object’s edge onto a 2D plane by rays perpendicular to that plane such that they are parallel to one another (unlike real-world)

Dashed lines represent hidden detials

Projections are independent of projection distance

## Projection depends on part orientation #

• Use judgement to select most useful/informative orientation
• Often, a projection is clearest when a significant flat surface of the object is parallel to the projection plane
• Left is a better pictorial view (it’s more 3D)
• Right is better because it’s face is parallel

## Multi-view orthographic projection #

• Usually can’t convey all information about an object using a single projection
• Use multiple projections from different viewpoints

## What is an orthographic projection? #

• Orthos: Greek for “right”, “true”, or “correct”
• Each projection is formed by rays perpendicular (at right angles) to its projection plane
• The different views of a multi-view drawing are taken from viewpoints at right angles to each other
• Multi-view orthographic projection is a standardized, accepted form of representing objects
• Graphos: drawing

## “Glass-box” interpretation #

• Need an agreed way to organize different projections on the page
• Imagine projecting object onto sides of a box
• Unfold the box onto the page
• So-called “third-angle” projection
• Will not necessarily show all six projections
• Projections are aligned

## Example of multi-view orthographic projection #

• Lines connecting a given point in adjacent views are always perpendicular to the “unfolding” line (of the “glass box”)

### View interpretation #

• Need to consider how many views needed to remove ambiguity

## Multiview characteristics #

• Inclined face
• Face in 2 views
• Line in 3rd view
• Oblique face
• Face in 3 views

## Which is the oblique face? #

### How many views? #

• Example: cut from sheet material
• Unlikely to be multiple levels of relief
• Projections of edges therefore unnecessary
• Grooves or etched patterns would be labeled as such

In this case, two views not enough to describe geometry completely – we need 3

• Thick enough material that there could conceivably be multiple levels of relief: side view needed
• In this particular example, all features pass through the full thickness of the material

Would any two views be enough to describe the geometry completely?

## First- vs third-angle orthographic projection #

• 3rd angle projection used in U.S.
• glass box convention

• 1st angle projection (Europe, Japan, India)
• top/bottom and left/right arrangement reversed

Example of why specifying 1st or 3rd angle matters

## ANSI standards (Y14.5) #

• Adopted by drafters and engineers to expedite the transfer of information
• Maximum information with the minimum drawing
• Will only cover highlights here
• Views
• At least two views (except flat sheet)
• Add views as required so the dimensions of the object can be defined entirely in true length measurements
• Add views as necessary for presentation clarity
• Solid lines
• Assumed to be intersections of planes or optical limits of cylinders
• Tangent edges are usually not shown, or shown using phantom lines
• Hidden lines
• Use to add information, clarity (good practice not to over-use)
• Use views requiring the fewest hidden lines
• Center lines
• Use to mark the centers of holes, or cylindrical surfaces ≥180º
• Circles
• Assumed to be intersections of cylinders and orthogonal planes
• Section views
• Used for clarification of internal geometries
• Explained in a later lecture

Small cuts on curved surfaces

Small radii, intersections of blended planar surfaces shown as a line

Parts with odd rotational symmetry Simplify to a symmetrical view even though that is not a strictly accurate projection

Tangent and non-tangent surfaces

• A line drawn where a curved surface meets a planar surface indicates no tangency: i.e. there is an abrupt change in the angle of the surface
• No drawn line indicates tangency: i.e.surface angle is continuous/smooth