l7 projection theory
TRANSCRIPT
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Engineering Drawing
Lecture 5
PROJECTION THEORYLecturer:Eng. Eman Al.SwaityEng.Heba hamad
University of PalestineCollege of Engineering & Urban PlanningFirst Level
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PROJECTIONMETHOD
PART 1
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TOPICS
Projection methods
Orthographic projection
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PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel
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PROJECTION THEORY
The projection theory is based on two variables:
1) Line of sight
2) Plane of projection (image plane or picture plane)
The projection theory is used to graphically represent
3-
D objects on 2-D media (paper, computer screen).
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Line of sightLine of sight is an imaginary ray of light between anobservers eye and an object.
Line of sight
Parallel projectionParallel projection
Line of sight
Perspective projectionPerspective projection
There are 2 types of LOS : parallel convergeand
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Plane of projectionPlane of projection is an imaginary flat plane whichthe image is created.
The image is produced by connecting the points where
the LOS pierce the projection plane.
Parallel projectionParallel projection Perspective projectionPerspective projection
Plane of projection Plane of projection
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Disadvantage of Perspective Projection
Perspective projection is notnot
used by engineer for manu-
facturing of parts, because
1) It is difficult to create.
2) It does not reveal exact
shape and size.Width is distorted
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OrthographicProjection
OrthographicProjection
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5
Orthographic projectionOrthographic projection is a parallel projection technique
in which the parallel lines of sight are perpendicular to the
projection plane
MEANING
Object views from top
Projection plane
1
2
3
4
5
1
2
3
4
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ORTHOGRAPHIC VIEWOrthographic viewOrthographic view depends on relative position of the object
to the line of sight.
Two dimensions of anobject is shown.
Three dimensions of an object is shown.
Rotate
Tilt
More than one view is neededto represent the object.
Multiview drawingMultiview drawing
Axonometric drawingAxonometric drawing
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Orthographic projection technique can produce either
1.1. Multiview drawingMultiview drawingthat each view show an object in two dimensions.
2.2. Axonometric drawingAxonometric drawingthat show all three dimensions of an object in one view.
Both drawing types are used in technical drawing for
communication.
NOTES
ORTHOGRAPHIC VIEW
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Axonometric (Isometric) Drawing
Easy to understand
Right angle becomes obtuse angle.
Circular holebecomes ellipse.
Distortions of shape and size in isometric drawing
AdvantageAdvantageDisadvantageDisadvantage Shape and angle distortion
Example
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Multiview Drawing
It represents accurate shape and size.AdvantageAdvantageDisadvantageDisadvantage Require practice in writing and reading.
Multiviews
drawing (2-view drawing)Example
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OrthographicProjection
PART 2
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TOPICS
Object representation
Glass box concept
Line convention
Orthographic projection of point ,line , plane , surface and object .
Multiview projection
Isometric Sketching
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OBJECT REPRESENTATION
Axonometric projection
Multiview projection
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MULTIVIEW PROJECTION
Three principle dimensionsof an object
Width Depth
Height
Width
H e i g h t
Depth
D e p t h
can be presented onlytwo in each view.
Adjacent view(s)
is needed tofulfill the sizedescription.
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1. Revolve the object with respect
to observer .
TO OBTAIN MULTIVIEWREPRESENTATION OF AN OBJECT
2. The observer move around the
object.
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REVOLVE THE OBJECT
Front view(Elevation) Right side view
Top view (Elevation)
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OBSERVER MOVE AROUND
Front view Right side view
Top view
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THE GLASS BOX CONCEPT
Bottom view
Left side view
Rear view
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Height
Width
D
e p t h
History
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MULTIVIEW PROJECTION
Click on the picture to play video
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MULTIVIEW PROJECTION
Click on the picture to play video
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MULTIVIEW PROJECTION
Click on the picture to play video
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MULTIVIEW PROJECTION
Click on the picture to play video
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OrthographicProjection
of Object Features
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OBJECT FEATURES
Edges are lines that represent the boundary
between two faces.
Corners Represent the intersection of two or
more edges.Edge
Corner
Edge No edge
No corner No corner
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Surfaces are areas that are bounded by edges
or limiting element.
Limitingelement
is a line that represents the last visible
part of the curve surface.
Surface Surface Surface
LimitLimit
OBJECT FEATURES
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A
B
PROJECTION OF POINT(S)
AF
BR
AT
BF AR
BT
AF AR
AT
BFB
R
BT
Equaldistance
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A
B
AF BF BR
AR
AT
BT
BR
AR AF BF
AT
BTTrue length
NORMAL LINETrue lengthPoint
Equallength
PROJECTION OF LINE
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A B
AF BF BR
AR
AT
BT
INCLINED LINEForeshortened
BR
AR
AFBF
Foreshortened
ATBT
True length
A
Equallength
PROJECTION OF LINE
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A B
AF
BF BR
AR
AT
BT
OBLIQUED LINE
A
Equallength
B
ForeshortenedForeshortened
Foreshortened
BR
AR
AF
BF
ATBT
PROJECTION OF LINE
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B C
A
PROJECTION OF PLANE
BF AF,C F C R AR,B R
AT
C T
NORMAL PLANE
Equallength
EdgeEdge
True size
C R
AR,B R AF,C F
BF
AT
BTC T
BT
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B C
BF AF
C R
AR,B R
AT
C T
INCLINED PLANE
A
Equallength
BT
C
C F
Edge
C R
AR,B R
Foreshortened
BTC T
AT
AF
C F
Foreshortened
BF
PROJECTION OF PLANE
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BC
BF
AF
C R
AR
AT
C T
OBLIQUED PLANE
A
Equallength
BT
C
C F
B
BR
Foreshortened
C R
AR
BR
AF
BF C F
Foreshortened
AT
BTC T
Foreshortened
PROJECTION OF PLANE
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You have to project the remaining surfaces which are invisible too !
PROJECTION OF OBJECTThe views are obtained by projecting all object
features to the picture plane.
(Elevation)
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s
s
s
PROJECTION OF OBJECT
(Elevation)
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PROJECTION OF OBJECT
(Elevation)
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Line Convention
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LINE CONVENTION
Precedence of coincide lines.
Hidden line drawing.
Center line drawing.
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PRECEDENCE OF LINE
VisiblelineOrder of importance Hiddenline Center line
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HIDDEN LINE PRACTICE
Hidden line should join a visible line, except itextended from the visible line.
Correct
No !
Join
Leavespace
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Correct No !
Hidden line should join a visible line, except itextended from the visible line.
Leavespace
Leavespace
HIDDEN LINE PRACTICE
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Hidden line should intersect to form L and Tcorners.
Correct
No !
L T
HIDDEN LINE PRACTICE
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Hidden arcs should start on a center line.
HIDDEN LINE PRACTICE
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CENTER LINE PRACTICEIn circular view, short dash should cross at theintersections of center line.
For small hole, center line is presented as thincontinuous line.
Center line should not extend between views.
Leave space Leave space
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Leave the gap when centerline forms a
continuation with a visible or hidden line
LeavespaceLeavespaceLeavespace
Leavespace
Center line should always start and end with
long dash.
CENTER LINE PRACTICE
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Isometric
Sketching
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2. Define an isometric axis.
3. Sketching the enclosing box.
4. Estimate the size an and relationship of each
details.
5. Darken all visible lines.
1. Place the object in the position which its shapeand features are clearly seen.
Sketch from an actual object
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STEPS
1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing box.
4. Add details.
5. Darken visible lines.
Sketch from an actual object
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1. Positioning object.
2. Select isometric axis.
3. Sketch enclosing
box.4. Add details.
Sketch from an actual objectSTEPS
5. Darken visible lines.
Note In isometric sketch/drawing), hidden lines are omittedunless they are absolutely necessary to completelydescribe the object.
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End of The LecturePROJECTION
THEORY