Projection of point

Projection of Point

Point may be defined as a circle having infinitesimal radius. A dot of pencil is an example of point.

Projection of point in first angle

In first angle of projection the point is placed above the HP and in front of VP. 

The distance above the HP               = a

The distance in front of the VP      = b

p’ = front view

p = top view

In angle of projection, horizontal plane is always rotate clockwise direction and the intersection of HP and VP is called reference line represent by XY. Draw reference line on a paper, above portion of XY line is VP and below portion is called HP shown in figure 2.

The distance above the HP is shown on vertical plane (VP), and the distance from VP is shown on horizontal plane (HP). Figure 2 shows the orthographic projection of the point in first angle of projection.

Figure 1: - Point in first angle of projection  

Draw the reference line XY

Draw point p’ above the XY at a distance ‘a’ above the HP

Draw projection from p’, perpendicular to XY and mark point p at a distance ‘b’ in top view as shown in figure 2.

Figure 2: - Projection of point in first angle of projection

Projection of point in Second angle

In this angle of projection point is placed behind VP and above HP shown in figure 3.

Same as first angle of projection, horizontal plane is always rotate clockwise direction and the intersection of HP and VP is called reference line represent by XY. Draw reference line on a paper, above portion of XY line represents both HP and VP because of overlapping of HP and VP. The front and top view of the point is lies above the XY line

Figure 3: - Point in Second angle of projection  

Draw XY line

Draw front view of the point at a distance of ‘a’ above the XY

Draw projection from front view perpendicular to XY

Mark a point p at a distance of ‘b’ from XY give the location of top view of the point shown in figure 4.

Figure 4: - Projection of point in second angle of projection

Projection of point in Third angle

Draw reference line on a paper, above portion of XY line represents HP and below portion of XY is VP shown in figure 5.

Figure 5: - Point in third angle of projection  

Draw XY line

Mark a point p above the XY line at a distance of ‘b’ called top view of the point

Draw the projection form p perpendicular to XY line

Mark a point p’ at a distance of ‘a’ below the XY called front view of point shown in figure 6.

Figure 6: - Projection of point in third angle of projection

Projection of point in Fourth angle

Draw reference line on a paper, below portion of XY line represents both HP and VP because of overlapping of HP and VP. The front and top view of the point is lies below the XY line shown in figure 7.

Figure 7: - Point in fourth angle of projection  

Draw XY line

Draw front view of the point at a distance of ‘a’ below the XY

Draw projection from front view perpendicular to XY

Mark a point p at a distance of ‘b’ from XY give the location of top view of the point shown in figure 8.

Figure 8: - Projection of point in fourth angle of projection

Points to remember : -

• Front view always drawn on vertical plane 
• Top view always drawn on horizontal plane
• Second angle projection and fourth angle of projection not use because of overlapping of the HP and VP.

Question: - 

What is the difference between First angle and third angle of projection?

Engineering drawing theory questions

Engineering Drawing is the universal language of engineers. The idea is drawn on a sheet by using point, line, and other drawing entities to give complete information or complete detail about the idea. Engineering drawings are those drawings that are used on the shopfloor to improve productivity. 

The sound knowledge of engineering drawing is essential to all engineering students. Engineering Drawing is difficult to understand for the first-year student of engineering. 

 

Orthographic Projection in First angle and Third angle of projection.

Draw the Orthographic projection of Given pictorial view as shown in figure 1 in first and third angle of projection.

Figure 1 Pictorial view of object

We are considering that the above object placed in first angle, and the arrow shows the direction of front view of the object.

The following steps are describe how to draw front view, top view and side view of the given object

• Draw the reference line XY

• Draw line a’b’ perpendicular to reference line.

• Draw a’f’ parallel to reference line.

• Draw f’e’, e’d’, d’c’, c’b’ to complete front view.

• Project all the corner of front view vertically downward and perpendicular to reference line.

• Draw af, ed, dj, jI, gh and fh to complete the top view of the object.

                                  Figure 2 Orthographic projection of object in First angle of projection 

For Right hand side View

• Transfer top view corner to X1 Y1 line and shift these points to XY by taking O1 as a centre and projects all the points vertically upward.

• Draw horizontal projection of all the corners from front view

• The intersection of vertical and horizontal projection gives the points of Right Hand Side View (RHSV)

For left hand side view

• Draw X2Y2 line perpendicular to XY

• From O2 draw a line inclined 45⁰ as shown in figure. This is another method to transfer points for side views.

• (Use any one method to draw side view of object)

• Transfer all the corners of Top View to inclined line and project vertically upwards.

• Again draw horizontal projection line to intersect vertical projection.

• Join the intersecting points in a sequence to complete the Left Hand Side View (LHSV).

Third angle of projection 

Figure 3 shows the drawing in third angle of projection. Follow above drawing procedure to complete drawing in third angle of projection. 

                                    Figure 3 Orthographic projection of object in Third angle of projection 

FV         -        Front View

TV         -       Top View

RHSV    -       Right hand side view

LHSV    -       Left hand side view

Engineering Drawing

Engineering Drawing is the universal language of engineers. The idea is drawn on sheet by using point, line and other drawing entities to give complete information or complete detail about idea. Engineering drawings are those drawings which are used in shop floor to improve the productivity. 

The sound  knowledge of the engineering drawing is essential to all engineering students. Engineering Drawing is difficult to understand for first year student of engineering. 

Introduction to Orthographic Projection

Projection

A projection is defined as an image or a drawing of an object made on a plane. All drawings used in the field of engineering are based on the principles of projection. Projections can be classified on the basis of the lines of sight and the positions of planes on which the drawing is made.

The lines of sight are popularly called projectors and the planes on which the drawings are made are called planes of projection.

Orthographic Projection

Orthographic is also called parallel line projection, the projectors are parallel to each other and also perpendicular to the plane.

Imagine that an observer looks at the object from the infinite distance, so the rays of sight is parallel to each other and perpendicular to the surface of the object. The view obtained on the Vertical plane (VP) is called Front View (FV) of the object.

Let us further assume that plane marked Horizontal Plane (HP). An observer looks the object in such a ways that the rays of sight is parallel to each other and perpendicular to HP, the view obtained on HP is called Top View (TV).

If observer looks the object in such a way that the rays of sight is parallel to each other and perpendicular to Profile Plane (PP), the view obtained on PP is called Side View (SV).

Figure 1

    The object is place above the HP and in-front of VP shown in figure 1. The front view obtained
    on VP, top view on HP and side view on PP are shown in figure 1.

    The views obtained in orthographic projection are two dimensional, so two or more than two
    views are required to describe the object.

   

    Figure 2 shows the Front View, Top View and Side View of the object on Vertical plane,
    Horizontal plane and Profile plane respectively. 

Figure 2 

Figure 3 

Figure 4

The horizontal plane and profile plane are rotates with respect to vertical plane. The direction of rotation is shown in figure 2. The final drawing is shown in figure 4.

Types of Orthographic Projection

First Angle

In first angle of projection the object is place above the horizontal plane and infront of vertical plane. The object lies between the vertical plane and observer.

The front view of the object draw above the reference line and top view of the object draw below the reference line.

Second Angle

In second angle of projection the object is place behind the vertical plane and above the horizontal plane. The vertical plane lies between object and observer.

Both front view and top view of the object lies above the reference line.

Third Angle

In third angle of projection the object is place below the horizontal plane and behind the plane vertical. The vertical plane lies between object and observer.

The front view of the object draw below the reference line and top view of the object draw above the reference line.

Fourth Angle

In fourth angle of projection the object is place infront of the vertical plane and below the horizontal plane. The object lies between vertical plane and observer.

Both front view and top view of the object lies below the reference line

Symbol of Projection