1. Categorize the 3D representations?
Boundary representation (B-reps) and space-partitioning representations.
2. What Boundary representation?
It describes a 3D object as a set of surfaces that separate the object interior from the environment. e.g. polygon facets and spline patches.
3. What space-partitioning representation?
This is used to describe interior properties, by partitioning the spatial region containing an object in to a set of small, non-overlapping, contiguous solids. e.g. octree.
4. What is Transformation?
Transformation is the process of introducing changes in the shape size and orientation of the object using scaling rotation reflection shearing & translation etc.
5. What is projection?
The process of displaying 3D objects on a 2D display is called as Projection.
6.What are the types of projection?
Perspective projection Parallel projection
7.What is parallel projection?
In a parallel projection, coordinate positions are transformed to the view plane along parallel lines.
8. What is Perspective projection?
For a perspective projection object positions are transformed to the view plane along lines that converge to a point called the projection reference point
9. Write short notes on active and passive transformations?
In the active transformation the points x and x| represent different coordinates of the same coordinate system. Here all the points are acted upon by the same transformation and hence the shape of the object is not distorted.
In a passive transformation the points x and x| represent same points in the space but in a different coordinate system. Here the change in the coordinates is merely due to the change in the type of the user coordinate system.
10. What is scaling?
The scaling transformations changes the shape of an object and can be carried out by multiplying each vertex (x,y) by scaling factor Sx,Sy where Sx is the scaling factor of x and Sy is the scaling factor of y.
11. What is shearing?
The shearing transformation actually slants the object along the X direction or the Y direction as required.ie; this transformation slants the shape of an object along a required plane.
12. What is reflection?
The reflection is actually the transformation that produces a mirror image of an object. For this use some angles and lines of reflection.
13. Distinguish between window port & view port?
A portion of a picture that is to be displayed by a window is known as window port. The display area of the part selected or the form in which the selected part is viewed is known as view port.
14. Define clipping.
Clipping is the method of cutting a graphics display to neatly fit a predefined graphics region or the view port.
15. What is covering (exterior clipping)?
This is just opposite to clipping. This removes the lines coming inside the windows and displays the remaining. Covering is mainly used to make labels on the complex pictures.
16. What is the need of homogeneous coordinates?
To perform more than one transformation at a time, use homogeneous coordinates or matrixes. They reduce unwanted calculations intermediate steps saves time and memory and produce a sequence of transformations.
17. Distinguish between uniform scaling and differential scaling?
When the scaling factors sx and sy are assigned to the same value, a uniform scaling is produced that maintains relative object proportions. Unequal values for sx and sy result in a differential scaling that is often used in design application
18. What is fixed point scaling?
The location of a scaled object can be controlled by a position called the fixed point that is to remain unchanged after the scaling transformation.
19.List out the various Text clipping?
ll-or-none string clipping - if all of the string is inside a clip window, keep it otherwise
ll-or-none character clipping – discard only those characters that are not completely inside the window. Any character that either overlaps or is outside a window boundary is clipped
Individual characters – if an individual character overlaps a clip window boundary, clip off the parts of the character that are outside the window.
20.What is the various representation schemes used in three dimensional objects?
Boundary representation (B-res) – describe the 3 dimensional objects as a set of surfaces that separate the object interior from the environment.
Space- portioning representation – describe interior properties, by partitioning the spatial region containing an object into a set of small, no overlapping, contiguous solids.
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