Tricky Visualization Interview Preparation Guide

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☛ Lightening conditions in the screen
☛ Assigned characteristics
☛ Degree of transparency
☛ How rough or smooth the surfaces are to be
☛ Exploded and cutaway views
☛ Three dimensional and stereoscopic views

☷ Modeling Transformation
☷ Viewing Transformation
☷ Projection Transformation
☷ Workstation Transformation

Basic problem for visualization techniques is called depth cueing.
Some 3D objects are without depth information visible line and surface identification To highlight the visible lines display visible lines as dashed lines removing the invisible lines.

Information visualization concentrates on the use of computer-supported tools to explore large amount of abstract data. The term "information visualization" was originally coined by the User Interface Research Group at Xerox PARC and included Dr. Jock Mackinlay. Practical application of information visualization in computer programs involves selecting, transforming and representing abstract data in a form that facilitates human interaction for exploration and understanding. Important aspects of information visualization are dynamics of visual representation and the interactivity. Strong techniques enable the user to modify the visualization in real-time, thus affording unparalleled perception of patterns and structural relations in the abstract data in question.

Basically, packages designed for graphics programming contain functions for setting primitives, attributes, and parameters for various graphics operations such as viewing and transformations. Packages designed for applications allow a user to create scenes in terms of the particular application, rather than in terms of graphics functions.

Besides the basic computer, some special devices and software may be required especially for computer graphics. For hardware, a special high-resolution, color monitor is often demanded and some input tools, e.g. mouse and joy-sticker, and hard-copy devices, e.g. high-resolution color printer, may be required. For software, some special purpose utilities (device-dependent and device-independent) are needed for handling processing in computer graphics.

Algorithm
Step 1:Input radius rx, ry and ellipse center(Xc, Yc)and obtain the first
point on the circumference of a circle centered on the origin as
(X0, Y0) = (0, ry)
Step 2: Calculate the initial values of the decision parameter in region 1 as
P10 = ry
2 - rx
2 ry + 1/4 rx
2
Step 3: At each position starting at Xk position in region 1,starting at k = 0,
perform the following test:
If Pk < 0, the next point to plot is (Xk+1, Yk) and
P1k+1 = P1k+2 ry
2Xk+1 + ry
2
Otherwise the next point is (Xk+1, Yk-1) and
P1k+1 = P1k+2 ry
2Xk+1 - 2ry
2 Yk+1 + ry
2
Step 4: Calculate the initial values of the decision parameter in region 2 as
P20 = ry
2 (X0+1/2)2+ rx
2 (Y0 - 1)2- rx
2 ry
2
Step 5: At each position starting at Yk position in region 2,starting at k = 0,
perform the following test:
If Pk > 0, the next point to plot is (Xk, Yk-1) and
22
P2k+1 = P2k - 2 ry
2Yk+1 + rx
2
Otherwise the next point is (Xk+1, Yk-1) and
P2k+1 = P2k - 2 ry
2Yk+1 - 2rx
2 Yk+1 + rx
2
Step 6: Determine symmetry points in the other three octants
Step 7: Move each pixel position(X, Y) onto the circular path centred on
(Xc, Yc) and plot the coordinate values as
X = X + Xc Y = Y + Yc
Step 8: Repeat steps for region 1 until 2 ry
2X>=2 ry
2Y

Both image and object space operations
Perform the basic function
Surface are sorted in order of decreasing depth
Surface are scan converted in order, starting with the surface of greatest depth
Often referred as painters algorithm
Test listed in the order of increasing difficulty
Surface do not overlap
Projections of the two surfaces on to the view plane do not overlap

❁ They are faster than pen plotters and very high quality printers.
❁ Recent electrostatic plotters include a scan-conversion capability.
❁ Color electrostatic plotters are available. They make multiple passes over the paper to plot color pictures.

Pixel phasing is an antialiasing technique, stair steps are smoothed out by moving the electron beam to more nearly approximate positions specified by the object geometry.

Winding number method is used to check whether a given point is inside or out side the polygon. In this method give a direction number to all the edges which cross the scan line. If the edge starts below the line and ends above scan line give direction as -1 . otherwise1. Fr polygons or two dimensional objects, the point is said to be inside when the value of winding number is nonzero.

Done by the projecting points to the display plane along the converging points Causes the objects farther from the viewing point should be smaller of the same sized object present here.

The production of the 2D display of the 3D scene is called projection. Project points on the object surface along the parallel lines on to the display plane. Different 2D views of objects can be produced by projecting the visible points.

Some objects do not maintain a fixed shape, but change their surface characteristics in certain motions or when in proximity to other objects. That is known as blobby objects. Example - molecular structures, water droplets.

The frame buffer used in the black and white system is known as bitmap which take one bit per pixel. For systems with multiple bits per pixel, the frame buffer is often referred to as a pixmap.

☼ It is an inexpensive technique.
☼ It has only four colors.
☼ The quality of the picture is not good when it is compared to other techniques.
☼ It can display color scans in monitors.

In Bresenham's approach the pixel position along a line path are
determined by sampling unit X intervals. Starting from the left end point(X0, Y0)of a
given line we step to each successive columns and plot the pixel whose scan line Y-value
is closest to the line path.Assuming the Kth step in process, determined that the pixel at
(Xk, Yk)decide which pixel to plot in column Xk+1.The choices are (Xk+1, Yk) and (Xk+1,
Yk+1)
Algorithm
Step 1: Input the line endpoints and store the left endpoint in (X0, Y0)
Step 2: Load (X0, Y0) in to the frame buffer
Step 3: Calculate constants
x,
y, 2
y, -2
x, and obtain the decision parameters as
P0 = 2
y -
x
Step 4 : At each Xk along the line, starting at k = 0, perform the following test
If Pk < 0, the next point to plot is (Xk+1, Yk) and
Pk+1 = Pk+2
y
Otherwise, the next point to plot is (Xk+1, Yk+1) and
Pk+1 = Pk+2
y - 2
x
Step 5: Repeat step 4
x times

They are optical effects to convert the sunlight or light from any other source to graphic form. Liquid crystal display is an example.

The emissive display converts electrical energy into light energy. The plasma panels, thin film electro-luminescent displays are the examples.

When a key is pressed on the keyboard, the keyboard controller places a code carry to the key pressed into a part of the memory called as the keyboard buffer. This code is called as the scan code.

The salient feature of computer graphics is the creation and manipulation of graphics (artificial images) by computer.
Computer graphics provides a tool called as motion dynamics which allows user to move object.

Resource Manager now handles access to all localized resources in an application. Any components that extend UIComponent, Formatter, or Validator now have a new resourceManager property, which lets you easily access the singleton instance of this manager. If you?re writing some other kind of class that needs to use the Resource Manager, you can call Resource Manager. get Instance() to get a reference to it.

Several processing units:
☛ Contains a special purpose processor, called video controller or display controller
☛ Video controller: A fixed area of the system memory is reserved for the frame buffer, and the video controller is given access to the framebuffer memory.
Tow registers are used to store the coordinates of the screen pixels.
The value is stored in the frame buffer for this pixel position is then retrieved and used to set the intensity of the CRT beam Initially the x register is set to 0 and the y register is set to ymax.
Then the x register is incremented by 1, and the process repeated for the next pixel on the top scan line.

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.

☛ There are three types of variable we use in information visualization. What are they? Explain them.
☛ Scatter-plot matrices are widely used in field of information visualization. What kind of data do it represent?
☛ What does a cyclic means in context of visualization?
☛ What is difference between rollover & brushing?
☛ What is sunburst model? How information can be represented in it?
☛ What are the major problems in 3D visualizations? How can they be solved?
☛ Describe several information visualizations that you believe will be possible and useful with the widespread adoption of virtual reality systems?
☛ Name & describe few techniques that are suitable for representing huge amount of data. What are their relative merits?
☛ Explain what Tufte meant by 'Data-Ink Maximization'?