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?

Example of hidden lines #

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

Representing threads use schematic representations

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

Pictorial views #

Review of isometric, oblique, and perspective #

Color; shading #

Section views #

Advanced projections #

Auxiliary views #

Additional notation #

Dimensioning #

Showing welds #