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Engineering Communications GL2 Geometric modelling Projection Systems

Engineering Communications GL2 Geometric modelling Projection Systems. Lecture presentations available on WWW: http://www.mame.mu.oz.au/~mcg/EngCom. A graphic is a representation on a 2-D surface of a 3-D scene. An artist may attempt to create a ‘realistic’ image.

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Engineering Communications GL2 Geometric modelling Projection Systems

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  1. Engineering Communications GL2Geometric modellingProjection Systems • Lecture presentations available on WWW: http://www.mame.mu.oz.au/~mcg/EngCom

  2. A graphic is a representationon a 2-D surface of a 3-D scene • An artist may attempt to create a ‘realistic’ image. • Note the use of perspective. • In fact, there are distortions in this picture, and it does not create the same projection on the retina as a real scene would.

  3. Meaning may be communicated better by deliberate distortion

  4. In engineering graphics: • a variety of types of distorted images are available to communicate meaning • strict rules apply to the construction and interpretation of these images • a universal language of graphic communication is thus achieved

  5. View point 3-D object Projection plane 2-D projection Projection rays Perspectiveprojection Engineering graphics are obtained by projection from the 3-D object to the viewing surface (the projection plane)

  6. Types ofprojection • Perspective projection is rarely used in manual drawing • Rather, we us a variety of orthographic projections, for which the projection rays are parallel

  7. Viewpointat  2-D projection Parallel projection rays 3-D object Projection plane In orthographic projection, the projection rays are parallel (view point at infinity)

  8. Perspective projection is useful for ‘non technical’ communications Perspective renderings for marketing, etc. are readily obtained with computer-aided drawing (CAD) systems

  9. Bertoline, et al. Fig. 9.2 Projection techniques Orthogonal (multiview) Axonometric Oblique Perspective

  10. Categories of orthographic projection Projectors Principalplane ofobject

  11. First quadrant Third quadrant Third-angle orthogonal projection Top horizontal plane Top view Glass projection box Leftsideview Frontvertical plane Front view Left profile plane

  12. horizontal plane depth vertical plane depth behind vertical plane width depth leftprofile plane height below horizontal plane height Third-angle orthogonal projection horizontal plane top (plan)view depth behind vertical plane leftsideview frontview left profile plane vertical plane

  13. TRIMETRIC DIMETRIC ISOMETRIC C C C A B B A A B z z z y y x x y Axonometric projection • Lines of sight perpendicular to projection plane • Principal axes all inclined to projection plane x Example: A=120º B=130º C=110º x:y:z = 1 : 0.808 : 0.938 Example: A=C=131.5º B=97º x : y : z = 0.5 : 1 : 1 Always: A = B = C = 120º x : y : z = 1 : 1 : 1

  14. Z A B projection plane 0.816  b C X Y Isometric projection isometric projection A = B = C = 120° a = b = 30° Scale ratios = (2/3) = 0.816 X : Y : Z = 1 : 1 : 1 For an isometric drawing, scale = FS on each axis

  15. Full scale  Scale = cot Full scale Oblique projection Principal object face parallel to projection plane

  16. Varieties of oblique projection Cavalier Cabinet General

  17. width depth depth Top view height Set square T-square Side view Front view Isometric sketch

  18. Projections of a cube compared ... 45º 60º 30º 30º Full scale Full scale Oblique (Cabinet) Half scale Isometric Full scale Full scale radius = 1 semi-minor axis = (1/2) semi-major axis = (3/2)

  19. Introduction to Cartesio software(download from EngCom homepage)

  20. Follow up • Read Bertoline: • § 4.5: Introduction to Projections • § 8.1: Projection Theory • § 8.2: Multiview Projection Planes • § 8.3:Advantages of Multiview Drawings • Do problems from Bertoline: • Probs 4.2(6)(47), 4.3(2)(6) • Check the EngCom web site

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