Perspective Projection

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Perspective Projection

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Perspective Projections ?????

• Perspective drawing differs from axonometric
  projection oblique projection in that the view
  is projected onto the picture plane by
  non-parallel projection lines merging to a single
  point called the station point (SP)
• SP can be regarded as the position of the
  viewers eye

VP
EL
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Vanishing Point

• A point in a perspective at which a set of
  parallel lines appear to converge
• Each set of parallel lines has its own vanishing
  point

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Convergence Principle

• Lines perpendicular to the picture plane appear
  to converge on the horizon line at the centre of
  vision
• Lines parallel to the picture plane DO NOT
  converge to a vanishing point but decrease in
  size according to their distance from the viewer

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One-point Perspective

• 1 vanishing point
• 2 axes or 1 face is parallel to the picture plane
  (PP)

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Two-point Perspective

• 2 vanishing points
• 1 axis of the object is parallel to the picture
  plane

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Three-point Perspective

• 3 vanishing points
• None of the axes is parallel to the picture plane

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Drawing Perspective Box

• Product sketching usually set the vanishing point
  far away from the drawing boundary, the result is
  an object that look small to medium size
• Draw 3 sets of parallel construction lines, 3
  lines per set. Longer lines make checking easier
• Draw the actual outlines with thicker, more solid
  lines
• Shade or render to taste

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Drawing Perspective Box

• Bringing the vanishing points closer to the
  drawing boundary, the result is an object that
  look more stereoscopic
• Draw 3 sets of construction lines, 3 lines per
  set.
• If the form sits upright
• the imaginative vanishing points for the first 2
  sets of line should line up horizontally
• the third set of line should be vertical
• Longer lines make checking easier

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Viewing Angle and Edge Pairs
Incorrect perspective the imaginative vanishing
points does not line up horizontally
Looking from high abovethe imaginative
vanishing points high above the sketch
Object tilted the 3 sets of edge rotate together
Looking from horizon the imaginative vanishing
points slightly above the sketch
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Common Errors

• All edges of the same direction must converge to
  one and only one vanishing point
• The vanishing point must locate at the side away
  from the viewer
• Hidden lines when extended, should intersect box
  corners

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View Angle and Visual Illusion

• For forms with inclined elements or edges on the
  faces, the effect of visual illusion can be very
  distracting, ending up with what looks like a
  very mis-shaped object
• The effect can be avoided by selecting another
  view angle

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Drawing Perspective Circle

• Perspective circle is not a true circle
• The first step to draw perspective circle is to
  draw a perspective square
• Divide the square with a cross
• Draw an ellipse with the long axis and short axis
  align to the diagonals

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Perspective Circle in Different Orientation
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Side-track Axonometric

• Axonometric projections have many variations
• Some have different levels of distortion among
  the different faces
• Some may have one of the sides with no distortion
  at all
• If the angles among X, Y and Z axes are the same,
  i.e. 120 degrees, emphasis is given to all the 3
  sets of planes. This type of projection is called
  Isometric

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Constructing Complex Form

• Imagine the faces as skewed drawing board
• The internal construction lines on the faces
  should match as they do in real-world
• Always draw construction lines on hidden faces to
  determine location of elements

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Starting off with the Cubic Form

• The cube is a convenient starting unit to
  construct other geometric forms

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Variations of Geometry

• Additive Forms

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Variations of Geometry

• Subtractive Forms

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Variations of Geometry

• Other Complex Forms

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Side-track Foreshortening

• Foreshortening refers to the contraction in size
  or length in the direction of depth in a
  perspective drawing for creating an illusion of
  distance or extension in space
• Such a phenomenon occurs when an object appears
  compressed when seen from a particular viewpoint,
  and the effect of perspective causes distortion.
• The orientation of the central axis of vision
  relative to the object determines the degree of
  foreshortening of individual spaces
• The more a plane is oblique to the picture plane,
  the greater degree of foreshortening occurs
• Only when a plane is parallel to the picture
  plane (as in orthographic projection) can its
  true shape be revealed
• For complex shapes, the effect of foreshortening
  can be very difficult to achieve convincingly,
  ending up with what looks like a very mis-shaped
  object.
• The linchpin is OBSERVATION and PRACTICE!