Projection is defined as an image or drawing of an object made on a plane. All drawings used in the field of engineering are based on the principles of projection. That is why engineering drawings are capable to precisely convey the external as well as internal features of objects in terms of their shape and size. Projections can be classified on the basis of line of sight and the position of plane on which the drawing is made. | Orthographic Projections Orthographic Projections Parallel projection technique Projectors normal to projection plane Projection Plane Projectors NOTE: CAD Systems typically use orthographic projection Orthographic Projection Categories Axonometric Three object faces visible No principal axes parallel/perpendicular to projection plane Multiview Only one object face visible One object face (., two principal axes) parallel to projection plane Axonometric Projections Trimetric – no equal angles All principal axes foreshortened unequally Classed according to angles made by principal axes when projected onto projection plane Dimetric – two angles are equal Two principal axes are equally foreshortened Isometric – all angles equal (iso equal, metric measure) All principal axes foreshortened equally Axonometric Projection Classes Axonometric Projection Classes Top View Front View Front View - Axes Only Isometric Scaling Lines parallel to any principal axis are foreshortened equally ( scaled proportionally) Measurements can be made parallel to any of the three principal axes NOTE: In a trimetric projection, measurements along a given principal axis are proportional; however, measurements along different principal axes are not scalable Isometric Projections All 3 principal axes equally foreshortened same scale Can be visualized as looking down the diagonal of a cube Trimetric Projection Isometric Projection Isometric Drawings Each axis is foreshortened to approximately 82% of its true length To correct for this, an isometric projection can be plotted at a scale of 1/.82 (~). This convenient approximation of an isometric projection is called an isometric drawing It can be shown that, in an isometric projection: Isometric Viewing About a vertical axis (45 ± 90n)º (n is an integer), then An isometric projection is obtained by rotating the view: Out of the horizontal plane, ± Front Front, Side Top, Front, Side Isometric Sketching In sketching an isometric . | Orthographic Projections Orthographic Projections Parallel projection technique Projectors normal to projection plane Projection Plane Projectors NOTE: CAD Systems typically use orthographic projection Orthographic Projection Categories Axonometric Three object faces visible No principal axes parallel/perpendicular to projection plane Multiview Only one object face visible One object face (., two principal axes) parallel to projection plane Axonometric Projections Trimetric – no equal angles All principal axes foreshortened unequally Classed according to angles made by principal axes when projected onto projection plane Dimetric – two angles are equal Two principal axes are equally foreshortened Isometric – all angles equal (iso equal, metric measure) All principal axes foreshortened equally Axonometric Projection Classes Axonometric Projection Classes Top View Front View Front View - Axes Only Isometric Scaling Lines parallel to any principal axis are foreshortened equally (
