Date post: | 19-Aug-2014 |
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Engineering |
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Orthographic Projection
TOPICS
Object representation
Glass box concept
Line convention
Multiview projection
OBJECT REPRESENTATION
Axonometric projection(Pictorial View)Multiview projection
MULTIVIEW PROJECTIONThree principle dimensionsof an object …
Width Depth
Height
Width
Hei
ght
Depth
Dep
th
… can be presented onlytwo in each view.
Adjacent view(s)is needed tofulfill the sizedescription.
1. Revolve the object with respect to observer.
TO OBTAIN MULTIVIEW REPRESENTATION OF AN OBJECT
2. The observer move around the object.
REVOLVE THE OBJECT
Front view Right side view
Top view
OBSERVER MOVE AROUND
Front view Right side view
Top view
THE GLASS BOX CONCEPT
Bottom view
Left side view
Rear view
HeightWidth
Dep
th
History
Standard Views of Primitive Solids
PROJECTION METHOD
Perspective
Oblique Orthographic
Axonometric Multiview
Parallel
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).
Line of sightLine of sight is an imaginary ray of light between an
observer’s eye and an object.
Line of sight
Parallel projectionParallel projection
Line of sight
Perspective projectionPerspective projection
There are 2 types of LOS : parallel convergeand
Plane of projectionPlane of projection is an imaginary flat plane which
the 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
Disadvantage ofPerspective 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
Comparison of Multi-view, Axonometric, oblique, and perspective projections
1. Multiview Projection 2. Axonometric Projection
3. Oblique Projection 4. Perspective Projection
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
51 2 3 4
Orthographic Projection
of Object Features
OBJECT FEATURESEdges are lines that represent the boundary
between two faces.
Corners Represent the intersection of two ormore edges.
Edge
Corner
Edge No edge
No corner No corner
Surfaces are areas that are bounded by edgesor limiting element.
Limitingelement
is a line that represents the last visiblepart of the curve surface.
Surface Surface Surface
LimitLimit
OBJECT FEATURES
PROJECTION OF OBJECTThe views are obtained by projecting all object features to the picture plane.
You have to project the remaining surfaces which areinvisible too !
s
s
s
PROJECTION OF OBJECT
PROJECTION OF OBJECT
Line Convention
LINE CONVENTION
Precedence of coincide lines.
Hidden line drawing.
Center line drawing.
PRECEDENCE OF LINEVisible
lineOrder ofimportance
Hiddenline
Centerline
HIDDEN LINE PRACTICEHidden line should join a visible line, except itextended from the visible line.
Correct
No !
Join
Leavespace
Correct No !
Hidden line should join a visible line, except itextended from the visible line.
Leavespace
Leavespace
HIDDEN LINE PRACTICE
Hidden line should intersect to form L and Tcorners.
Correct
No !
L T
HIDDEN LINE PRACTICE
Hidden arcs should start on a center line.
HIDDEN LINE PRACTICE
CENTER LINE PRACTICEIn circular view, short dash should cross at the intersections of center line.
For small hole, center line is presented as thin continuous line.
Center line should not extend between views.
Leave space Leave space
Leave the gap when centerline forms a continuation with a visible or hidden line
Leavespace
Leavespace
Leavespace
Leavespace
Center line should always start and end withlong dash.
CENTER LINE PRACTICE