Projections:Projection, as we refer to it here, is when you reduce the three dimensions of a real or virtual (computer) object to two dimensions. This is necessary to represent the object on a computer screen or a flat piece of paper.Parallel Projection:With parallel projection, all of the projection lines are parallel to each other. The parallel projection lines means that edges that are parallel on the real object are also parallel in the projection. This allows for the least amount of distortion of features within the object.Orthographic projection:When the projectors are parallel to each other and also perpendicular to the view plane, the projection is called orthographic projection.Multi-view projection:With a multi-view projection, the projection lines are oriented parallel to one of the principle axes of the object. These edges define one of the principle axes which, in turn, defines one of the primary dimensions of the object.Axonometric Projections:A method of projection which has the advantage of containing a true plan, and can therefore set up from drawings already in existence for other purposes. The plan is turned through 45 degrees, vertical lines being drawn from the angles on the plan to show the elevations.1. Trimetric Projection:Type of an axonometric projection in which the three spatial axes are represented as unequally inclined to the drawing surface and equal distances along the axes are drawn unequal.

2. Di-metric Projection:

Di-metric projection is defined as a way of drawing an object so that one axis has a different scale than the other two axis in the drawing.

3. Isometric Projection: In technical drawing, a three-dimensional view of an object can be drawn to scale with three perpendicular edges at 120 degrees to each other, and with the vertical edges vertical.

Oblique Projection: It is defined as a pictorial view of an object showing its elevation, plan, or section to scale with parallel lines projected from the corners, at 45 degrees or any other angle, indicating the other sides.General oblique: When the projectors make angle other than 45 of 63.26 degrees the drawing is called general oblique.

1. Cavalier Projection:In the cavalier case, lengths perpendicular to the projection plane are preserved, and as in all parallel projections, lengths parallel to the projection plane are preserved. Thus in this case lengths in all three directions are preserved. For example the projection of a unit cube using a cavalier projection will be an object whose sides are all of length 1, although angles will not be 90 of course.

2. Cabinet Projection:In the cabinet case, lines perpendicular to the projection plane project at 1/2 their length, while lines parallel to plane project at full length. Thus in this case there is a foreshortening which is more realistic to the eye, while at the same time allowing measurements to be made from a drawing, if one remembers the factor 2 scaling in the one direction. For example the projection of a unit cube using a cabinet projection will be an object 2 of whose sides are of length 1, with one side of length 1/2. Angles will not be 90 between these sides of course.

Perspective Projection:Perspective projection is a form of pictorial drawing that gives the illusion of depth onto a flat surface, very similar to that of viewing of the object through the human eye. In comparison to other types of projection systems, for example orthographic and oblique, the spectator is viewing the object from infinity. In perspective, the projected rays radiate from the object to a single point at a given distance from the object.

1. One point Perspective:One point perspective has also been called central perspective and single-point perspective. These obviously describe a situation where only one direction point is needed to draw an entire form or scene. This point, itself, is at times called the central vanishing point, principal vanishing point or center of vision.

2. Two point Perspective:A mathematical system for representing three-dimensional objects and space on a two-dimensional surface by means of intersecting lines that are drawn vertically and horizontally and that radiate from two points called vanishing points.

3. Three point Perspective:Linear perspective in which parallel lines along the width of an object meet at two separate points on the horizon and vertical lines on the object meet at a point on the perpendicular bisector of the horizon line.