GL2:1 Engineering Communications GL2 Geometric modelling Projection Systems Lecture presentations available on WWW:

GL2:2 A graphic is a representation on 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.

GL2:3 Meaning may be communicated better by deliberate distortion

GL2:4 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

GL2:5 Projection plane 3-D object View point Projection rays 2-D projection Engineering graphics are obtained by projection from the 3-D object to the viewing surface (the projection plane) Perspective projection

GL2:6 Perspective projection is rarely used in manual drawing Types of projection Rather, we us a variety of orthographic projections, for which the projection rays are parallel

GL2:7 Projection plane 3-D object View point at  In orthographic projection, the projection rays are parallel (view point at infinity) Parallel projection rays 2-D projection

GL2:8 Perspective projection is useful for ‘non technical’ communications Perspective renderings for marketing, etc. are readily obtained with computer-aided drawing (CAD) systems

GL2:9 Bertoline, et al. Fig. 9.2 Projection techniques Orthogonal (multiview)Axonometric ObliquePerspective

GL2:10 Categories of orthographic projection Principal plane of object Projectors

GL2:11 Top horizontal plane Front vertical plane Left profile plane Third-angle orthogonal projection Top view Front view Left side view Glass projection box First quadrant Third quadrant

GL2:12 Third-angle orthogonal projection vertical plane horizontal plane left profile plane left side view depth horizontal plane vertical plane left profile plane depth behind vertical plane height below horizontal plane top (plan ) view width height fron t view depth depth behind vertical plane

GL2:13 DIMETRIC A C TRIMETRIC Axonometric projection Lines of sight perpendicular to projection plane Principal axes all inclined to projection plane A C B Example: A=120º B=130º C=110º x:y:z = 1 : : B Example: A=C=131.5º B=97º x : y : z = 0.5 : 1 : 1 x y z ISOMETRIC A C B Always: A = B = C = 120º x : y : z = 1 : 1 : 1 x y z x y z

GL2:14 projection plane Isometric projection isometric projection A = B = C = 120° AB C    =  = 30° XY Z Scale ratios =  (2/3) = X : Y : Z = 1 : 1 : 1 For an isometric drawing, scale = FS on each axis 0.816

GL2:15 Scale = cot  Oblique projection  Full scale Principal object face parallel to projection plane

GL2:16 Cavalier Cabinet General Varieties of oblique projection

GL2:17 Isometric sketch T-square Set square depth height width Top view Front viewSide view depth

GL2:18 45º 60º Full scale Half scale radius = 1 semi-major axis =  (3/2) semi-minor axis =  (1/2) Isometric Oblique (Cabinet) Projections of a cube compared... 30º

GL2:19 Introduction to Cartesio software (download from EngCom homepage)

GL2:20 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