Transcript Station point (SP - Engineering Graphics Live

PERSPECTIVE PROJECTION
Prof.T.JEYAPOOVAN
Department of Mechanical Engineering
Hindustan Institute of Technology and Science
Chennai-603103, India
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Perspective Projection
• Perspective projection is used
to draw the three dimensional
picture of an object as it
appears to the human eye.
• Perspective drawings are
usually drawn for large objects
such as buildings.
• In perspective projection, the
picture of the object is obtained
in a plane known as the picture
plane by assuming that the
view is taken from a specific
point known as the station
point.
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Perspective Nomenclature
• Ground plane (GP) is a horizontal reference plane on which the
object will be resting or placed.
• Station point (SP) is the observer’s eye.
• Picture plane (PP) is a vertical reference plane on which
perspective view of the object is obtained when the object is viewed
from the station point.
• Ground line (GL) is the intersection line of PP and GP.
• Horizon plane (HP) is also a horizontal reference plane which is
parallel to GP and passing through the station point.
• Horizon line (HL) is the intersection line of PP and HP.
• Visual rays are imaginary lines drawn to join various corners of the
object to the station point (SP) which pierce the picture plane. These
piercing points are marked in top view and are projected to front
view to get the perspective projection of an object.
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Perspective Projection
• Consider the arrangement of the
reference planes, position of the
object and observer shown earlier.
• When viewed from the top, the
line of intersection of the planes
alone can be seen in top view.
• In this case, the object is placed
behind PP and the observer
(station point) stands in front of
PP as shown in Fig.
• Also, consider the front view of
the arrangement of the reference
planes, object, observer and other
elements seen as shown in Fig.
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Visual ray method
• In visual ray method, the TV
and FV of the object and
station point (sp) in both the
views are located.
• Then visual rays from sp
connecting various corners of
the object in TV and FV are
drawn.
• The piercing points of these
rays with picture plane are
marked in TV and projected to
FV to get perspective
projection of the object.
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Example 1: Draw the perspective view of a square pyramid of base 30 mm,
side and height of apex 45 mm rests on GP. The nearest edge of the base
is parallel to and 20 mm behind the picture plane. The station point is
situated at a distance of 70 mm in front of the PP and 40 mm to the right of
the axis of the pyramid and 60 mm above the ground.
• Understand and visualize
the reference planes and
object placed on GP.
• Understand and draw the
line of intersection of the
planes, object and observer
in TV and FV.
• Draw the rays connecting
object corners and SP in TV
and FV.
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• Draw the visual rays
connecting object corners
and SP in TV and FV.
• Mark piercing points of the
visual rays in top view and
project and mark them to the
corresponding rays in front
view.
• Join the points, draw the
visible and hidden edges to
complete the perspective
projection of the pyramid.
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Vanishing point method
• The vanishing point is an
imaginary point which lies at
the level of horizontal plane
and it is at a finite distance
from the station point (SP)
where the visual rays from SP
pierces the picture plane.
• The piercing points of these
rays with picture plane are
marked in TV and projected to
FV to get perspective
projection of the object.
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Example 2: A rectangular block 30 × 20 × 15 mm is lying on the ground
plane, on one of its largest faces. A vertical edge is in the PP and the
longer edge containing that face makes an angle of 30° with the picture
plane. The station point is 50 mm in front of the picture plane, 30 mm
above the ground plane and lies in the central plane which passes
through the center of the block. Draw the perspective view of the block by
vanishing point method.
• Draw TV of the block and rays
connecting object corners and SP.
• Draw a line passing through SP
and parallel to an inclined edge of
the solid to mark vanishing points.
• Draw the perspective of the edge
of the rectangular block which
touches the PP.
• Mark the piercing points of the
rays in TV and project them to FV
• Join visible and hidden edges to
complete perspective projection.
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Example 3: A cube of edge 5 cm rests with one of the faces on the
ground, the nearest vertical edge being 1 cm to the left of the station point
and 2.5 cm behind PP. A face containing the nearest vertical edge is
inclined at 60° to the PP. The station point is 7.5 cm above the ground and
10 cm in front of PP. Draw the perspective view of the cube.
• Draw the TV and rays connecting
object corners and SP.
• Draw a line passing through SP and
parallel to an inclined edge of the
cube to mark vanishing points.
• Draw perspective of an edge of
cube by using the line of true
height.
• Mark the piercing points of the rays
in TV and project them to FV
• Join visible and hidden edges to
complete perspective projection of
the cube.
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Tips to draw Perspective Projection
• The visible and invisible edges are usually identified
through visualization.
• The visible edges are marked by considering the edges
in the front portion of the solid which lie within the cone
angle formed by the visual rays in top view with SP.
• The details printed in figure are neglected by the users
while preparing the fair drawing of perspective.
• Complete the perspective projection by drawing dark
lines for the visible portion of the object.
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REFERENCE BOOKS
1. Jeyapoovan T, “Lesson Plans for Engineering
Graphics”, 2010, Vikas Publishing House Pvt
Ltd, New Delhi.
2. Jeyapoovan T, “Engineering Drawing and
Graphics”, 2011, Vikas Publishing House Pvt
Ltd, New Delhi.
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End of Lesson 13
Thank You
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