3-D to Orthographic Projection. Orthographic Projection – 3D. (i) Axonometric –
Isometric. (ii) Oblique. (iii)Perspective. Why do we need 3-D Pictorial Drawings?
Lecture – 6 http://home.iitk.ac.in/~mukesh/
PRACTICE
PRACTICE
3-D to Orthographic Projection
Orthographic Projection – 3D (i) Axonometric – Isometric (ii) Oblique (iii)Perspective
Why do we need 3-D Pictorial Drawings?
Parallel to Picture plane (only one face seen)
Rotated about vertical axis (two faces seen)
Rotated about vertical & profile Axes (three faces seen)
Can get Infinite 3-d views – needs uniformity and standardization
S
R,U
T
R,S
T
First Position – one face seen
U
S
Rotate about Vertical axis by 450 Two faces seen
T R,U
S
R
T
U
S
Three mutually perpendicular Edges, SR, RU and RT now make equal angle of 120o with each other and are called
ISOMETRIC AXES
R U
T
Then Rotate about profile axis by 350 (three faces seen) Projections are still orthographic What these rotations have done? SR, RU, RT all foreshortened but by equal lengths
Schematic presentation of concept
Quiz: How much AB is foreshortened? Isometric Axes
A
B
30o
30o
One Can draw isometric Figure with the help of Isometric box Two types : (i) Isometric Projection – Take lines as foreshortened (ii) Isometric drawing - Disregard foreshortening take actual length
A
B
A. Isometric projection: foreshortened (81/100) B. Isometric drawing: No foreshortening (100/100) No difference in shape - Isometric drawing larger in Linear proportion of 1.23:1. Most common form is to use isometric drawing
Important •
All lines parallel to isometric axes – Isometric lines
•
All isometric lines are foreshortened equally (81/100)
•
All other non-isometric lines may or may not foreshorten
•
Foreshortening ratio of such lines may vary disproportionately
•
Projections of parallel lines are parallel.
•
All measurements can only be marked on isometric lines
ISOMETRIC SCALE
4
3 le a c S ar 2 l u g e R
1
0
1
3e al c S 2 tric me o Is
0
45
4 0
30
0
Make Isometric scale : foreshortened to 81/100 to Be used in Isometric projection
12
20
20
10
A
B
12
10
C
Decide width and depth directions – height direction is fixed.
D C
B A
D C
A
B
Boxing Method
Top
Now start drawing Isometric
Front
Right Side
Top
300
300
Identify hidden lines Front Now erase the hidden lines
Right Side
Top
Now erase hidden portion of ellipse
Front
Right Side
Top
Isometric
Front
Right Side
Top
Now start drawing Isometric
Front
Right Side
Draw base as in previous isometric Now draw the additional surface Top
Smoothly join both ellipses Identify hidden lines and erase
