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Engineering Communications GL2 Geometric modelling Projection Systems. Lecture presentations available on WWW: http://www.mame.mu.oz.au/~mcg/EngCom. A graphic is a representation on a 2-D surface of a 3-D scene. An artist may attempt to create a ‘realistic’ image. - PowerPoint PPT Presentation
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GL2:1
Engineering Communications GL2
Geometric modellingProjection Systems
• Lecture presentations available on WWW:
http://www.mame.mu.oz.au/~mcg/EngCom
GL2:2
A graphic is a representationon a 2-D surface of a 3-D scene
• An artist may attempt to create a ‘realistic’ image.
• Note the use of perspective.
• In fact, there are distortions in this picture, and it does not create the same projection on the retina as a real scene would.
GL2:3
Meaning may be communicated better by deliberate distortion
GL2:4
In engineering graphics:
• a variety of types of distorted images are available to communicate meaning
• strict rules apply to the construction and interpretation of these images
• a universal language of graphic communication is thus achieved
GL2:5
Projection plane
3-D objectView point
Projection rays
2-D projection
Engineering graphics are obtained by projection from the 3-D object to the viewing surface (the projection plane)
Perspectiveprojection
GL2:6
• Perspective projection is rarely used in manual drawing
Types ofprojection
• Rather, we us a variety of orthographic projections, for which the projection rays are parallel
GL2:7
Projection plane
3-D object
Viewpointat
In orthographic projection, the projection rays are parallel (view point at infinity)
Parallel projection rays
2-D projection
GL2:8Perspective projection is useful for ‘non technical’ communications
Perspective renderings for marketing, etc. are readily obtained with computer-aided drawing (CAD) systems
GL2:9
Ber
toli
ne, e
t al.
Fig
. 9.2
Projection techniques
Orthogonal (multiview) Axonometric
Oblique Perspective
GL2:10
Parallel top ro jectio n p lane
Normal top ro jectio n p lane
Orthogonal
Inclined top ro jectio n p lane
Normal top ro jectio n p lane
Axonometric
Parallel top ro jectio n p lane
Inclined top ro jectio n p lane
Oblique
Orthographic pro jectio n( P aralle l p ro jecto rs )
Categories of orthographic projection
Principalplane ofobject
Projectors
GL2:11
Top horizontal plane
Frontvertical plane
Left profile plane
Third-angle orthogonal projection
Top view
Front view
Leftsideview
Glass projection box
First quadrant
Third quadrant
GL2:12
Third-angle orthogonal projection
vertical plane
horizontal plane
left profile plane
leftsideview
depth
horizontal plane
vertical plane
leftprofile
plane
depth behindvertical plane
height belowhorizontal plane
top (plan)
view
width
heightfrontview
depth depth behindvertical plane
GL2:13
DIMETRIC
A
CTRIMETRIC
Axonometric projection• Lines of sight perpendicular to projection
plane• Principal axes all inclined to projection
plane
A
C
B
Example:A=120º B=130º C=110ºx:y:z = 1 : 0.808 : 0.938
B
Example:A=C=131.5º B=97º x : y : z = 0.5 : 1 : 1
xyz
ISOMETRIC
A
C
B
Always:A = B = C = 120ºx : y : z = 1 : 1 : 1
xy
z
xyz
GL2:14
projection plane
Isometric projection
isometric projection
A = B = C = 120°
A B
C
= = 30°
X Y
Z
Scale ratios = (2/3) = 0.816X : Y : Z = 1 : 1 : 1
For an isometric drawing, scale = FS on each axis
0.816
GL2:15
Scale = cot
Oblique projection
Full scale
Full scale
Principal object face parallel to projection plane
GL2:16
Cavalier
Cabinet
General
Varieties of oblique projection
GL2:17Isometric sketch
T-square
Set square
dep
thh
eig
ht
width
Top view
Front viewSide view
depth
GL2:18
45º
60º
Full scale
Full scale
Full
scale
Full scale
Half s
cale
radius = 1
semi-major axis = (3/2)
semi-minor axis = (1/2)
Isometric
Oblique (Cabinet)
Projections of a cube compared ...
30º30º
GL2:19
Introduction to Cartesio software(download from EngCom homepage)
GL2:20
Follow up• Read Bertoline:
– § 4.5: Introduction to Projections– § 8.1: Projection Theory– § 8.2: Multiview Projection Planes– § 8.3:Advantages of Multiview Drawings
• Do problems from Bertoline:– Probs 4.2(6)(47), 4.3(2)(6)
• Check the EngCom web site