orthographic projection

1. Orthographic projection
• In engineering drawing the meaning of the
word projection is to project(Throw ) an object
on to a plane by means of straight lines.
• The representation of any three dimensional
object placed in front of a two dimensional
plane is called Projection of an object on that
plane.

3. contents
 Introduction to orthographic projections
First angle projection method
Third angle projection methods
Drawing orthographic projection of simple
pictorial view

4. Introduction to orthographic
projection
• In orthographical projection it is assumed that
observer is at infinite distance and rays or
projection lines are parallel to each other and
perpendicular to the plane of projection.(e.g
board and students, theater)

5. System of orthographic projection

6. How to identify the quadrant of object
Sr.no Quadrant Position of the
object with
respective planes
of projection
1 First Above HP,in front
of VP
2 Second Above HP,Behind
V.p
3 Third Below HP.Behind
VP
4 Fourth Below HP,in front of
VP

7. Position of the views on a plane paper
when object is lying in four quadrant.
Position of the object Position of the top view Position of the front view
First quadrant Below XY axis Above XY axis
Second quadrant NA NA
Third quadrant Above XY Below XY
Fourth quadrant NA NA

8. Sketches speaks more………….

9. First angle projection method
• When an object is situated in the first
quadrant, The method of projection is said to
be FIRST ANGLE PROJECTION METHOD.
• When an object is situated in third quadrant
,The method of projection is sai to be THIRD
ANGLE PROJECTION METHOD.

10. Important facts about first angle projection
method
1.The object is situated in first quadrant.
2.The object lies between the observer and the
principal plane.
3.The orthographic projection of an object obtained on
the vertical plane is front view.
4.The orthographic projection of an object obtained on
HP is TV and lies below the XY line.
5.LHSV is drawn on the right side of FRONT VIEW.
6.RHSV is drawn on the left side of FRONT VIEW.

11. Now you can analyze better………..

12. Procedure of preparing orthographic views
by using first angle projection method
1.Find out the maximum size of box which will contain
the object.
2.Draw FV, TV, and RHSV of the imaginary box.While
drawing the views of the box maintain proper spacing
of the views with reference lines XY
3.Now Draw the portion which is visible from front in
FRONT VIEW.
4.The portion of the object which will be visible from
the top is drawn in top view.

13. Third angle projection method
When object is situated in third quadrant,The
method of projection is said to be THIRD ANGLE
PROJECTION METHOD.

14. THANK YOU