Chapter 4
ORTHOGRAPHIC PROJECTION
Dr. Pham Minh Tuan
Principle of projection
S: Station point
A: Projected object
(P): Plane of projection
SA: Projector
A’: Projection of A onto (P)
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Projection methods
PERSPECTIVE PROJECTION
The projectors are starting from a station point (observer’s eye) to
each point of part.
Produce realistic views but does not preserve relative proportions
of an object dimensions.
Normally used to perform large objects.
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Projection methods
PARALLEL & OBLIQUE PROJECTION
Projector lines are parallel to each other.
Parallel projection Oblique projection
Cannot show the distance from the station point to the object.
Normally used to perform small objects.
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Characteristics of orthographic projection
Characteristic 1:
Orthographic projection of a line is also a line.
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Characteristics of orthographic projection
Characteristic 2:
Orthographic projection of two parallel lines are also two parallel lines.
AB // CD → A'B' // C'D'
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Characteristics of orthographic projection
Characteristic 3:
Through orthographic projection, the length ratio of two parallel lines are
unchanged.
AB/CD = A'B'/C'D'
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Orthographic projection
The projection of point A onto (P) is a unique point A’.
From the point A' on (P), it is able to find infinite different points
which have A' as their projection.
→ To perform an object in space, at least 2 orthographic
projections are required.
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Orthographic projection
Project the object onto three projection planes which are
perpendicular to each other.
Rotate the projection planes to match the drawing plane.
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Orthographic projections of a point
PROJECTIONS OF A POINT ONTO 2 PLANES
A1: Front view A P1: Vertical plane
A2: Plan (Top) view of A P2: Horizontal plane
A1A2: Projection line
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Orthographic projections of a point
PROJECTIONS OF A POINT ONTO 3 PLANES
A3: Side (Left) view of A
P3: Side/Profile plane
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Orthographic projections of a line
A GENERAL LINE
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Orthographic projections of a line
A LINE PARALLEL TO THE VERTICAL PLANE
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Orthographic projections of a line
A LINE PARALLEL TO THE HORIZONTAL PLANE
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Orthographic projections of a line
A LINE PARALLEL TO THE SIDE PLANE
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Orthographic projections of a line
A LINE NORMAL TO THE VERTICAL PLANE
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Orthographic projections of a line
A LINE NORMAL TO THE HORIZONTAL PLANE
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Orthographic projections of a line
A LINE NORMAL TO THE SIDE PLANE
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Orthographic projections of a plane
A GENERAL PLANE
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Orthographic projections of a plane
A PLANE NORMAL TO THE VERTICAL PLANE
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Orthographic projections of a plane
A PLANE NORMAL TO THE HORIZONTAL PLANE
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Orthographic projections of a plane
A PLANE NORMAL TO THE SIDE PLANE
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Orthographic projections of a plane
A PLANE PARALLEL TO THE HORIZONTAL PLANE
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Orthographic projections of a plane
A PLANE PARALLEL TO THE VERTICAL PLANE
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Orthographic projections of a plane
A PLANE PARALLEL TO THE SIDE PLANE
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Orthographic projections of a “L plane” (1)
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Orthographic projections of a “L plane” (2)
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Orthographic projections of a “L plane” (3)
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Orthographic projections of a “L plane” (4)
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Orthographic projections of a “L plane” (5)
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Orthographic projections of a “L plane” (6)
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END OF CHAPTER 4