Ch.5 Pictorial Drawings
Objective: Learn how to construct three types of
pictorial drawings – Isometric, oblique, and
perspective
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Isometric drawings (6.1 & 6.2)  Theory of isometric projection
(fig5.9), Position of isometric axes (fig6.10 to 12), Standards for
hidden lines, center lines, and dimensioning (fig6.13 to 15),
isometric drawing construction (fig6.17 to 42)
Oblique drawings (6.3)  Oblique projection theory &
classification (fig6.46 to 50), object orientation rules (fig5.51 to
55), dimensioning (fig6.65), oblique drawing construction (fig6.56
to 64)
Perspective drawings (6.4-6.7)  Perspective vs. orthogonal
(fig6.69), vanishing point position and ground line position
(fig6.17 & 6.73), classification of perspective drawing (fig6.74),
perspective drawing variables selection (6.7).
Comparison of Isometric, oblique, and
perspective drawings
Examples
Perspective
Isometric drawings
Depending on where you place isometric axes,
you get different views (Use the most effective
position to meet your need)
About isometric and non-isometric lines
and planes
True-length distances can
only be measured along
isometric lines, that is,
lines run parallel to any of
the isometric axes.
Dealing with hidden lines and center lines
in isometric drawings
Hidden lines are omitted unless they are absolutely
necessary. Center lines are drawn only for showing
symmetry or for dimensioning. Normally center
lines are not shown.
Dimensioning in isometric drawings
Constructing an isometric
drawing using the
Boxing-In method
Box in from
the outmost
shape to
inside details.
What if you have non-isometric lines?
Remember that true-length
distances can only be
measured along isometric
lines, that is, lines run parallel
to any of the isometric axes.
What if you have curves?  use the Offset Coordinate method works.
Another example
of the Offset
Coordinate
method
Oblique Drawings
Oblique projection is a
form of parallel projection
in which the projectors are
parallel to each other but
are not perpendicular to
the projection plane.
Common oblique angles
Oblique drawing types: cavalier, cabinet,
and general oblique
Some hints to select the most important
object face
In oblique projection, first, the object face that is
placed parallel to the frontal plane will be drawn true
size and shape.
Dimensioning in oblique drawings
In oblique drawings, dimensions lie in the
plane of the surface to which they apply, and
unidirectional text placement is used.
Dimension text
may need to be
changed because
only the cavalier
oblique projection
gives true depth.
Constructing an oblique drawing using the
Box-In method
Constructing an oblique drawing using the
Offset Coordinate method
When we have arcs and curves, this
method is always the easiest method.
Perspective drawings
Terms that you want to be familiar with: horizon
line, ground line, station point, picture plane
(projection plane), and vanishing point.
Position of the
vanishing point and
ground line and
resulting perspective
projections
One-, two-, and
three-point
perspective
drawings
4 variables in perspective
drawings:
Distance of object from
picture plane
Position of station point
Position of ground line
Number of vanishing points