THREE DIMENSIONAL GRAPHICS

1.What are blobby objects?

Some objects do not maintain a fixed shape, but change their surface characteristics in certain motions or when in proximity with other objects. These objects are referred to as blobby objects, since their shapes show a certain degree of fluidness.

2.What are spline curves? (AU NOV/DEC 2011 & NOV/DEC 2012)

The term spline is a flexible strip used to produce a smooth curve through a designated set of points. In computer graphics, the term spline curve refers to any composite curve formed with polynomial sections satisfying specified continuity conditions at the boundary of the pieces.

3.How to generate a spline curve?

A spline curve is specified by giving a set of coordinate positions called as control points. These control points are then fitted with piece wise continuous parametric polynomial functions in one of the two ways. When polynomial sections are fitted so that the curve passes through each control point, the resulting curve is said to interpolate the set of control points. When the polynomials are fitted to the general control point path without necessarily passing through any control point the resulting curve is said to approximate the set control points.

4.What are called control points?

The spline curve is specified by giving a set of coordinate positions, called control points, which indicates the general shape of the curve.

5.When is the curve said to interpolate the set of control points?

When polynomial sections are fitted so that the curve passes through each control point, the resulting curve is said to interpolate the set of control points.

6.When is the curve said to approximate the set of control points?

When the polynomials are fitted to the general control-point path without necessarily passing through any control point, the resulting curve is said to approximate the set of control points.

7.What is called a convex hull?

The convex polygon boundary that encloses a set of control points is called the convex hull.

8. Explain about Bezier curves.

This is a spline approximation method. A beizer curve section can be fitted to any number of control points. The number of control points to be approximated and their relative position determine the degree of the Beizer polynomial. As with the interpolation splines, a beizer curve can be specified with boundary conditions, with a characterization matrix, or with blending functions.

9.What are the various 3D transformations?

The various 3D transformations are a. translation, b. reflection, c. scaling, d. rotation and e. shearing.

10.What is shear transformation? (AU MAY/JUNE 2012 IT)

Shearing transformations can be used to modify object shapes. They are also used in 3D viewing for obtaining general projection transformation.

 A z-axis 3D shear:

1 0 a 0

SH_Z =   0 1 b 0

0 0 1 0

0 0 0 1                        

Parameters a and b can be assigned any real value.