In 3D Graphics, which of the following statements about perspective and parallel projection is/are true?
P: In a perspective projection, the farthest an object is from the center of projection, the smaller it appears.
Q: Parallel projection is equivalent to a perspective projection where the viewer is standing infinitely far away
R: Perspective projections do not preserve straight lines.
Choose the correct answer from the code given below:Code:
P and R only
P, Q and R
Q and R only
P and Q only
Perspective projection is representing or drawing objects which resemble the real thing.
Perspective projection preserves the straight line.
In perspective projection, objects that are far away appear smaller, and objects that are near appear bigger.
Parallel lines do not remain parallel.
Distance and angles are not preserved.
Parallel Projection :
In this projection drawing objects looks less realistic.
In this projection parallel lines remains parallel.
Angles are not preserved in this projection.
It is good for exact measurements.
In 3D Graphics, which of the following statement/s is/are true ?
P: Back-face culling is an example of an image-precision visible-surface determination.
Q: Z-Buffer is a 16-bit, 32-bit, or 64-bit field associated with each pixel in a frame buffer
that can be used to determine the visible surface at each pixel.
Choose the correct answer from the code given below :;Code :
Neither P nor Q
P and Q
→ Back-face culling (an object space algorithm) works on 'solid' objects which you are looking at from the outside. That is, the polygons of the surface of the object completely enclose the object.
→ Back-face culling is not an example of an image-precision visible-surface determination.
→ Back-face culling can very quickly remove unnecessary polygons. Unfortunately there are often times when back-face culling can not be used. For example if you wish to make an open-topped box - the inside and the outside of the box both need to be visible, so either two sets of polygons must be generated, one set facing out and another facing in, or back-face culling must be turned off to draw that object.
1. Back faces: faces of opaque object which are “pointing away” from viewer.
2. Back face culling – remove back faces (supported by OpenGL).
→ TRUE: Z-Buffer is a 16-bit, 32-bit, or 64-bit field associated with each pixel in a frame buffer that can be used to determine the visible surface at each pixel.
In a 3d-rendering engine, when an object is projected on the screen, the depth (z-value) of a generated pixel in the projected screen image is stored in a buffer (the z-buffer or depth buffer).
A z-value is the measure of the perpendicular distance from a pixel on the projection plane to its corresponding 3d-coordinate on a polygon in world-space.
Z-buffer requires 2 type of buffers to be filled: Depth buffer and Frame buffer
The amount of memory required by depth buffer in terms of bits is 512 x 512 x 24 = 6291456
The amount of memory required by frame buffer in terms of bits is 512 x 512 x 24 = 6291456
Total memory is required is sum of both depth and frame buffer memories = 6291456 + 6291456 = 12582912 bits which is equivalent to 1.5 MB(1.5x1024x1024x8)
the number of axes cut by the projection plane
the centre of projection
the number of axes which are parallel to the projection plane
the perspective projections of any set of parallel lines that are not parallel to the projection plane
→This point is called the vanishing point. A vanishing point corresponds to every set of parallel lines.
It is a depth sort algorithm
No limitation on total number of objects
Comparisons of objects is done
z-buffer is initialized to background colour at start of algorithm
To begin with, a buffer containing the closest depth at each pixel location is created parallel to the image buffer. Each location in this depth buffer is initialized to negative infinity.
Since the algorithm processes objects one at a time, the total number of polygons in a picture can be arbitrarily large.
800 x 600
1024 x 768
1280 x 1024
1920 x 1440
Given file size is 8M bytes= 8*1024**1024*8=83,88,608
From the options,
From the above , option A and B are less than file size.
From that two , maximum one is option B.
Hidden line removal
Biquadratic Bezier patch
Circular patch only
Bilinear Bezier patch