In addition to two coordinates X and Y, an extra coordinate Z is added. 3D graphics techniques and applications are very fundamental for entertainment, games, and computer-aided design industries.
Every personal computer has 3D graphics components. They are increasingly being used by other applications.
The z-coordinate is discarded by the Parallel projection and the parallel lines from each vertex on to the object and till it intersect the view plane, the objects are extended. A direction of projection is specified instead of center projection.
The distance from the center of projection to the project plane is infinite in parallel projection. The projected vertices are connected by line segments that correspond to the connections on original object.
For exact measurements, parallel projections are mostly used. Parallel lines remain parallel and angles are not preserved. Some of the types of parallel projections are as follows:
The direction of the projection is normal to the projection of the plane in Orthographic projection. Different types of orthographic projections are:
The object is better viewed than orthographic projection in oblique projection.
Oblique projections are of two types − Cavalier and Cabinet. The Cavalier projection makes 45° angle with the projection plane. The length of the projection is same as that of the cavalier projection. The foreshortening factors of all the three principle directions are equal.
63.4° angle with the projection plane is made with the Cabinet projection. In Cabinet projection, lines perpendicular to the viewing surface are projected at ½ their actual length. Both the projections are shown in the following figure −
The projections that show more than one side of the object are called as axonometric orthographic projections. Isometric projection is the most common projection where the projection plane intersects each coordinate axis in the model coordinate system at an equal distance. The isometric projection is depicted below:
There is finite distance between center of projection to project plane and the object size varies inversely with the distance that seems to be more realistic.
The parallel lines do not remain parallel and the distance and angles are not preserved. Instead, at a single point, center of projection or projection reference point, all the parallel lines converge. Three types of perspective projections appear such as:
All the three types of perspective projection is depicted below:
The Z coordinate is translated along X and Y coordinates. The 3D translation is similar to that of 2D translation. An object is moved into different position on the screen and the effect of transition is depicted below:
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