This chapter discusses pictorial projections used in technical drawing. It explains the differences between axonometric and oblique projections, and between isometric projections and isometric sketches. It provides instructions for creating isometric and oblique sketches from actual objects or multiview drawings. Key topics covered include types of axonometric and oblique projections, foreshortening in isometric projections, orienting isometric axes, and techniques for sketching ellipses and irregular curves in isometric views.

1. Chapter 5
Pictorial
Projection
1

2. Objectives
ExplainExplain the difference between axonometric and oblique
projection.
ExplainExplain the difference between isometric projection and
isometric sketch (or draw).
CreateCreate an isometric and oblique sketches from an actual
object and given multiview drawing.
After completing this chapter, the students will be able to
2

3. Topics
Pictorial projections
- Axonometric
- Oblique
Isometric sketch
Oblique sketch
3

4. Pictorial
Projections
4

5. Pictorial Projection
A
B
C
D
Parallel & normal
to picture plane
Line
of
sight
A
B
C
D
A
B
C
D
Line
of
sight
Parallel & oblique
to picture plane
A
D
C
B
Axonometric Projection Oblique Projection
5

6. Axonometric Projection
A
B
C
D
Line
of
sight
A
B
C
D
6

7. Axonometric Projection
Type of axonometric drawing
a
b c2. Dimetric Two angles are equal.
b
a
c3. Trimetric None of angles are
equal.
a
b c
1. Isometric All angles are equal.
A
B
C
DA
B
C
D
Axonometric axis
Axonometric axis
Axonometric axis
7

8. A
B
C
D
Line
of
sight
Oblique Projection
A
D
C
B
8

9. Oblique Projection
A
D
C
B
B
C D
A
Oblique drawing angle
30o
45o 60o
Type of Oblique drawing
45o
45o
1) Cavalier 2) Cabinet
Full
scale Half
scale
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10. Isometric projection
vs.
Isometric sketch
10

11. Isometric Projection
Rotate 45°
about vertical axis
Tilt forward
(35o
16’)
All edges foreshorten
about 0.8 time.
11

12. Isometric sketch
Isometric sketch is an isometric view that is drawn
in full size.
Isometric projection
(True projection)
Isometric drawing
(Full size)
Forshorten
Full scale 12

13. Orientation of Isometric Axes
Isometric axes can be arbitrarily oriented to create
different views of a single object.
Regular
isometric
Reverse axis
isometric
Long axis
isometric
View point is looking
down on the top of
the object.
View point is looking
up on the bottom of
the object.
View point is looking
from the right (or left)
of the object.
13

14. Distance in Isometric Sketch
Isometric line is the line that run parallel to
any of the isometric axes.
Isometric axes
True-length distances show along isometric lines.
Nonisometric lines
14

15. Isometric
Sketching
15

16. 2. Define an isometric axis.
3. Sketching the enclosing box (or cylinder).
4. Estimate the size an and relationship of each
details.
5. Darken all visible lines.
1. Place the object in the position which its shape
and features are clearly seen.
Sketch from an actual object
16

17. STEPS
1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing box.
4. Add details.
5. Darken visible lines.
Sketch from an actual object
17

18. 1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing
box.
4. Add details.
Note In isometric sketch/drawing), hidden lines are omitted
unless they are absolutely necessary.
STEPS
5. Darken visible lines.
Sketch from an actual object
18

19. 1. Interprete the meaning of lines/areas in
multiview drawing.
2. Locate the lines or surfaces relative to isometric
axis.
Sketch from multiview drawing
19

20. Front View
Top View
Side View
Example 1 : Object has only normal surfaces
Bottom View
Bottom
Front
Side
Side
Front
Top
Regular
Reverse
W
D
H
H
DW
20

21. Example 2 : Object has inclined surfaces
W
H
θ
D
y
x Front View
y
x
Nonisometric line
21

22. A
A
B
B
C D
E
D
EF
F
x
y
Front View
Regular
C
Example 4
Reverse
23

23. Isometric ellipse
In isometric drawing, a circle appears as an ellipse.
2. Construct an isometric square.
3. Sketch arcs that connect the
tangent points.
Sketching Steps
1. Locate the center of an ellipse.
24

24. 3. Construct a perpendicular
bisector from each tangent point.
4. Locate the four centers.
5. Draw the arcs with these centers
and tangent to isometric square.
Sketching Steps
Four-center method is usually used when drawn an
isometric ellipse with drawing instrument.
2. Construct an isometric square.
1. Locate the center of an ellipse.
Isometric ellipse
25

25. Example 5
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26. Irregular Curve in Isometric
1. Construct points along the
curve in multiview drawing.
2. Locate these points in the
isometric view.
3. Sketch the connecting lines.
Steps
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