Orthographic Projection | Theory of Projection Part 2 | Lecture 5 |Engineering Graphics| 4 Quadrants

Orthographic projection is a means of representing three-dimensional objects in two dimensions. It is a form of parallel projection, in which all the projection lines are orthogonal(perpendicular) to the projection plane.
It is used to produce working drawings in either a first or third angle projection and shows each side of a design without perspective, i.e a 2D drawing of a 3D object. It shows an object from every angle to help the manufacturer's production.
In this drawing, it is assumed that the object is at infinity. The shape of an object is seen in actual size in such drawing. A plane of projection is an imaginary surface on which images are projected imaginably. Then it is transferred to the paper. This plane is faced toward the object whose view is to be prepared.
Generally, three views of an object are prepared. These are Top View, Front View, and Side View. If the plane is kept in a vertical position, then it is called the vertical plane. If the plane is kept in a horizontal position, then it is called the horizontal plane. The plane, horizontal or vertical, which are kept perpendicular to each other are called Principal Planes. If these are placed in such a way that they form four Quadrants.
If the first Quadrant is used to draw the projections, then this system is called First Angle System. In this system, the top view is placed below the reference line while the front view is upward and the side view is by the side of the front view.
If the third quadrant is used, then this system is called the Third Angle System. In the third angle system, the top view is upward while the front view is downward and the side view is towards, aside from the front view.

Watch this video to understand the basics of orthographic projection.

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Theory of Projection Part 1-Introduction | English | Lecture 4 | Engineering Graphics | Dr.S.Malligarjunan
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