To obtain points on an ellipse, circle should be enclosed in a square and mid points of sides and intersection of diagonals with circle are 8 points. Lines are drawn through se points, parallel to sides of square.

When an object has its three faces inclined to picture plane, its perspective is called oblique perspective also called 3 point perspective as edges of object converge to three vanishing points.

The measuring line or line of heights is trace or line of intersection with picture plane, of vertical plane containing point or points whose heights are to be determined. Heights of points lying in different vertical plane can be measured from ir respective line of heights.

The oblique projection represents three dimensional objects on projection plane by one view only. This type of drawing is useful for making an assembly of an object and provides directly a production drawing of object for manufacturing purpose.

Cavalier projection is one of type of oblique projection in which receding lines are drawn to full size scale and projectors are inclined at 30 degrees, 45 degrees, 60 degrees to plane of projection.

In orthographic projection, isometric projection parallel faces in solid which having same dimensions will show true exact sizes or in proportions and also in parallel faces but in perspective view parallel line, edges, faces show differ in dimensions.

In perspective projection, line drawn through station point and perpendicular to picture plane is sometimes called line of sight or axis of vision is called perpendicular line.

The distance points are equidistant from center of vision distance of each from centre of vision being equal to distance of station point from picture plane perspectives of all horizontal lines inclined at 45 degrees to picture plane converge to a distance points on horizon line.

When receding lines are drawn to half size scale n oblique projection is cabinet projection. When receding lines are drawn to full size scale n oblique projection is cavalier projection.

The perspective will show object reduced in size when it is placed behind picture plane. If object is moved nearer picture plane size of perspective will increase and vice versa.