Lecture 6 ( ): Theory of Multi-view Orthographic Projections

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1 Lecture 6 ( ): Theory of Multi-view Orthographic Projections Dr. Sharad Gokhale Civil Engineering Department, IIT Guwahati 208, M-Block, Academic Complex sharadbg@iitg.ernet.in Telephone #: 2419

2 Multi-view Orthographic Projections

3 Terms and definition Projection image or the act of obtaining an image of an object In technical drawing we call it a view Method we use projection method to obtain a view of an object

4 Orthographic Projections It is a technical drawing in which different views of an object are projected on different reference planes Different Reference planes(principal planes): Horizontal Plane(HP), Vertical Frontal Plane(VP) SideOrProfilePlane(PP) Different views: Front View(FV), Top View(TV), Side View(SV)

5 Perspective Projection System

6 Projection System Projection lines Plane of Projections (POP) Perspective Parallel

7 Projection System Projection lines Plane of Projections (POP) Perspective (Convergent projection) Three basic elements: i. Object ii. Observer iii. POP Parallel Projection

In orthographic projection, projections from all points of the

8 Projection of an Object The outline on the plane of projection shows how the object appears to the observer. In orthographic projection, projections from all points of the object extend parallel to each other and perpendicular to the plane of projection.

9 X Y

10 2 nd Quad. VP 1 st Quad. Y Observer X Y HP X 3 rd Quad. 4 th Quad. This quadrant pattern, If observed along x-y line ( inredarrow direction) will exactly appear as shown on right side and hence, It is further used to understand illustration properly.

11 Methods of Drawing Orthographic Projections First Angle Projections Method Here views are drawn by placing object in 1 st Quadrant ( FV above X-Y, TV below X-Y ) Third Angle Projections Method Here views are drawn by placing object in 3 rd Quadrant. ( TV above X-Y, FV below X-Y ) FV X Y X Y TV Symbolic presentation of both methods with an object standing on HP (ground) on it s base. NOTE:- HP term is used in 1 st angle method & ground term is used in 3 rd angle method of projections G TV FV L

12 Planes PRINCIPAL PLANES HP AND VP Profile Plane (P.P.) AUXILIARY PLANES Auxiliary Vertical Plane (A.V.P.) Auxiliary Inclined Plane (A.I.P.) A.V.P. to HP & to VP

13 Planes & Views (first angle method) This is a pictorial set-up of all three planes. Arrow direction is a normal way of observing the object. But in this direction only VP and a view on it (FV) can be seen. The other planes and views on those can not be seen. Procedure to solve above problem:- To make those planes also visible from the arrow direction, i) HP is rotated 90 0 downward, ii) PP, 90 0 in right side direction. This way both planes are brought in the same plane containing VP. Y VP FV PP LSV X Y X TV HP HP IS ROTATED DOWNWARD 90 0 AND BROUGHT IN THE PLANE OF VP. PP IS ROTATED AWAY IN RIGHT SIDE 90 0 AND BROUGHT IN THE PLANE OF VP. ACTUAL PATTERN OF PLANES & VIEWS OF ORTHOGRAPHIC PROJECTIONS DRAWN IN FIRST ANGLE METHOD OF PROJECTIONS

14 First angle projection FOR T.V. IN THIS METHOD, THE OBJECT IS ASSUMED TO BE SITUATED IN FIRST QUADRANT MEANS ABOVE HP & INFRONT OF VP. OBJECT IS INBETWEEN OBSERVER & PLANE. VP PP X FV TV LSV Y HP ACTUAL PATTERN OF PLANES & VIEWS IN FIRST ANGLE METHOD OF PROJECTIONS

15 THIRD ANGLE PROJECTION FOR T.V. IN THIS METHOD, THE OBJECT IS ASSUMED TO BE SITUATED IN THIRD QUADRANT ( BELOW HP & BEHIND OF VP. ) PLANES BEING TRANSPERENT AND INBETWEEN OBSERVER & OBJECT. X LSV TV FV Y ACTUAL PATTERN OF PLANES & VIEWS OF THIRD ANGLE PROJECTIONS

16 Orthographic projections - points, lines, planes, and solids To draw projections of any object, one must have the following information Object (with it s description, well defined) Observer (always observing perpendicular to respective reference plane) location of object (means it s position with reference to HP & VP) Terms above & below with respective to HP and terms infront & behind with respective to VP form 4 quadrants. Objects can be placed in any one of these 4 quadrants

17 UNDERSTANDING PROJECTIONS To make and interpret drawings you need to know how to create projections and understand the standard arrangement of views. You need to be familiar with the geometry of objects and be able to visualize a 3D object that is represented in a 2D drawing.

a front view shows the true shape and size of surfaces

18 The system of views is called multi-view projection. Each view provides certain definite information. e.g. a front view shows the true shape and size of surfaces that are parallel to the front of the object. Views of Objects

In fact, any principal view of a 3D object shows only two of the three principal dimensions; the third is found in an

19 Principal Dimensions The three principal dimensions of an object are width, height, and depth. The front view shows only the height and width of the object and not the depth. In fact, any principal view of a 3D object shows only two of the three principal dimensions; the third is found in an adjacent view. Height is shown in the rear, left-side, front, and right-side views. Width is shown in the rear, top, front, and bottom views. Depth is shown in the left-side, top, rightside, and bottom views.

20 Envision the object in a Glass Box To understand the standard arrangement of views on the sheet of paper

21 To draw the views on a sheet of paper, imagine the six planes of the glass box being unfolded to lie flat. Note the six standard views (front, rear, top, bottom, right side, left side).

22 The Glass Box Unfolded Lines extend around the glass box from one view to another on the planes of projection. These are the projectors from a point in one view to the same point in another view.

23 The Orthographic Projection The front, top, and right-side views of the object shown now without the folding lines.

24 Necessary Views The top, front, and right-side views, arranged together, are called the three regular views because they are the views most frequently used. A drawing should contain only the views needed to clearly and completely describe the object.

25 View Selection Use minimum number of views to describe the object Select the most descriptive views

27 How to project Side Views? Projecting across meter line Projecting through arcs Projecting through 45 degree projectors

28 Projecting across meter line X1 FV LHSV X 45 o Y Meter line TV Y1

29 Projecting through 45 o projectors X1 FV LHSV X Y 45 o projectors TV Y1

30 Projecting through arcs X1 FV LHSV X Y Arcs TV Y1

34 Three basic views (FV, TV, SV) will provide Top view complete information about the real object Top View

35 VIEWS OF SURFACES The three orientations that a plane surface can have to the plane of projection are normal, inclined, and oblique. A plane surface that is perpendicular to a plane of projection appears on edge as a straight line

36 Standard Views of Primitive Solids

37 Ex. 1 & 2: Draw the three principal views of the objects shown In fig 9.12 (a)and9.13(b)

38 Ex.3&4:Fromthepictorial view of the objects shown Infig9.14(a)and9.15(b) DrawFV,TV,RHSV

ME 111: Engineering Drawing

ME 111: Engineering Drawing Lecture 5 12-08-2011 Orthographic projection and Projection of Points Indian Institute of Technology Guwahati Guwahati 781039 1 Orthographic Projection A parallel projection