Projection and view

• Projection system and terms in projection
• classification of projection
  • Parallel projection
    • orthogonal
      • Two view
      • Three view
      • Multi view
    • Pictorial projection
      • Oblique
        • Cavalier
        • Cabinet
      • Perspective
      • Axonometric
        • Isometric projection
        • Dimetric projection
        • Trimetric projection
  • Angular projection
• TOP VIEW, FRONT VIEW, SIDE VIEW, left side VIEW , right side VIEW, bottom view, back view
• First Angle projection
• Second Angle projection
• Third Angle projection
• Fourth Angle projection
•  Difference b/w First Angle projection and Third Angle projection
• tetrahedron
• hexahedron
• octahedron
• dodecahedron
• icosahedron

Parallel projection : Parallel projection is a method used to represent three-dimensional objects on a two-dimensional surface. It involves projecting lines of sight that remain parallel to each other throughout the process. This technique is particularly useful in technical and engineering drawings where precision is crucial, as it maintains the object’s dimensions and proportions accurately

• Lines of Projection: Remain parallel to each other and do not converge.
• Realism: Does not create a realistic view of depth as perspective projection does.
• Accuracy: Maintains accurate dimensions and proportions of the object.
• Applications – Parallel projection is widely used in engineering and architectural drawings for its ability to provide precise measurements and representations of objects

Types of Parallel Projection

Orthographic Projection:

• Definition: Involves projecting an object onto a series of perpendicular planes, typically resulting in multiview drawings such as front, top, and side views.
• Subtypes:
  • Multiview Projection: Displays multiple views of an object, often including first-angle, second-angle, third-angle, and fourth-angle drawings.
  • Axonometric Projection: Includes isometric, dimetric, and trimetric projections, which are used to represent objects in a three-dimensional manner without perspective.

• Pictorial projections : Pictorial projections in engineering drawing are used to represent three-dimensional objects on a two-dimensional plane, providing a more realistic view compared to orthographic projections.
• The main types of pictorial projections are:
  • Oblique
    • Cavalier
    • Cabinet
  • Perspective
  • Axonometric
    • Isometric projection
    • Dimetric projection
    • Trimetric projection
• Isometric Projection
  • All three axes (X, Y, and Z) are inclined at 120° to each other or the angles between the axes are all the same.
  • The lengths along each axis are equally foreshortened.
  • It provides a clear view of the object’s shape and dimensions.
• Dimetric Projection
  • Two axes are equal, while the third is at a different angle
  • Two axes have the same level of foreshortening, while the third axis is different.
  • It is less common but used when an object has two dominant dimensions.
• Trimetric Projection
  • All three axes are at different angles
  • All three axes have different foreshortening.
  • It provides the most realistic view but is complex to construct.

• Oblique Projection
  • Projectors are parallel but at an angle other than 90° to the picture plane.
  • The front face is drawn true to size, while the depth is represented at an angle (typically 30°, 45°, or 60°).
  • Two types:
    • Cavalier Projection: Full depth is retained.
      • Uses a 45° angle for the projection.
    • Cabinet Projection: Depth is halved to reduce distortion.
      • Uses a 30° angle for the projection, reducing the size of the object’s depth dimension.

Difference Between Orthogonal and Oblique Projections

• Perspective Projection
  • Mimics how the human eye perceives objects.
  • Lines converge towards a vanishing point (one-point, two-point, or three-point perspective).
  • Used for realistic representations in architecture and product design.

• Overview of Projection Angles
  • In orthographic projection, objects are represented in two dimensions by projecting their views onto planes. The main projection methods are First Angle Projection and Third Angle Projection. There is no standard Second Angle Projection or Fourth Angle Projection in common use.
• First Angle Projection
  • Placement: The object is placed in the first quadrant, between the observer and the projection planes.
  • View Order: The views are arranged with the top view below the front view, and the side view on the opposite side.
  • Plane State: The projection plane is considered solid (opaque).
  • Usage: Widely used in India, Europe, and Canada.
• Third Angle Projection
  • Placement: The object is placed in the third quadrant, with the projection plane between the observer and the object.
  • View Order: The top view is above the front view, and the side view is adjacent to it.
  • Plane State: The projection plane is considered transparent.
  • Usage: Commonly used in the United States and Australia.

Difference Between First Angle and Third Angle Projections

• Second Angle Projection and Fourth Angle Projection are not standard methods in orthographic projections. The primary distinction lies between First Angle and Third Angle projections, which differ in object placement and view arrangement.

• Tetrahedron
  • Faces: 4 equilateral triangles
  • Edges: 6
  • Vertices: 4
  • Vertex Configuration: 3 triangles meet at each vertex
  • Properties: Smallest of the Platonic solids, often associated with fire in Plato’s philosophy.
• Hexahedron (Cube)
  • Faces: 6 squares
  • Edges: 12
  • Vertices: 8
  • Vertex Configuration: 3 squares meet at each vertex
  • Properties: Dual of the octahedron, associated with earth.
• Octahedron
  • Faces: 8 equilateral triangles
  • Edges: 12
  • Vertices: 6
  • Vertex Configuration: 4 triangles meet at each vertex
  • Properties: Dual of the cube, associated with air in Plato’s philosophy.
• Dodecahedron
  • Faces: 12 regular pentagons
  • Edges: 30
  • Vertices: 20
  • Vertex Configuration: 3 pentagons meet at each vertex
  • Properties: Associated with the universe, its faces symbolize the 12 signs of the zodiac.
• Icosahedron
  • Faces: 20 equilateral triangles
  • Edges: 30
  • Vertices: 12
  • Vertex Configuration: 5 triangles meet at each vertex
  • Properties: Associated with water in Plato’s philosophy, has the largest number of faces among the Platonic solids.
• These solids are all convex polyhedra with regular polygon faces, where the same number of faces meet at each vertex. They are named after Plato, who associated them with elements and the universe in his philosophical works.

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