Orthographic Projections
Orthographic Projections
Parallel projection technique
Projectors normal to projection plane
Projection Plane
Projectors
NOTE: CAD Systems typically use orthographic projection
Orthographic Projection Categories
Axonometric
Three object faces visible
No principal axes
parallel/perpendicular to
projection plane
Multiview
Only one object face
visible
One object face (i.e., two
principal axes) parallel to
projection plane
Axonometric Projections
Classed according to angles made by principal axes
when projected onto projection plane
Trimetric – no equal angles
All principal axes foreshortened unequally
Dimetric – two angles are equal
Two principal axes are equally
foreshortened
Isometric – all angles equal (iso
equal,
metric
measure)
All principal axes foreshortened equally
Axonometric Projection Classes
Isometric Projections
All 3 principal axes equally foreshortened
same scale
Can be visualized as looking down the
diagonal of a cube
CAD viewing tool
Isometric Views
An isometric projection is obtained by rotating
the viewing direction:
About a vertical axis (45 ± 90n)º (n is an
integer), then
Out of the horizontal plane, ±35.26º
Isometric Drawings
It can be shown that, in an isometric projection:
Each axis is foreshortened to approximately 82%
of its true length
In plotting an isometric view in a CAD system,
can correct for this by plotting at a scale of 1/.82
(~1.22).
An unforeshortened
isometric view is
called an isometric
drawing
Isometric Sketching
In sketching an isometric view, principal axes are
aligned as shown below:
Isometric Scaling
Lines parallel to any principal axis are
foreshortened equally ( scaled proportionally)
Measurements can be made parallel to any of
the three principal axes
AB, CD measurable
BC, DE not measurable
NOTE: In a trimetric projection, measurements along a given
principal axis are proportional; however, measurements along
different principal axes are not
Isometric Sketch of a Cut Block
Isometric Sketch of a Cylinder
Isometric Sketch of a Cube with Holes
Isometric Sketch with Arcs
Orthographic Projections