Question

Question 1: Illustrate the Rendering pipeline of the graphic systems. Answer: Question 2: Discuss the Synthetic camera model and differentiate it with a natural viewing model (eye). Answer: Question 3: Discuss the 3D viewing pipeline of the graphic systems. Answer: Question 4: Explain the object space or local coordinate systems. Answer: Question 5: Elaborate the world space or world coordinate systems. Answer: Question 6: Discuss the steps of 3D viewing process. Answer:

Answer 1

Ans 1: Answer in the image.
Ans 2: Synthetic Camera Model-

• In Computer Graphics, we use a synthetic camera model to mimic the behaviour of real camera.
• In this model, we avoid the inversion by placing the film plane, called the projection plane, in front of the lens.
• The clipping rectangle or clipping window determines the size of the image.

Synthetic camera model vs natural viewing system(eye)-

• Absolute versus subjective measuring of light: Simply speaking, the human eye is a subjective device. This means that your eyes work in harmony with your brain to create the images you perceive: Your eyes are adjusting the focus (by bending the light through the lens in your eyeballs) and translating photons (light) into an electrical impulse your brain can process. From there onwards, it’s all about your brain: It is continuously readjusting its colour balance according to the lighting context. In other words, our eyes know what must be seen as red or white or black etc.
• A camera, on the other hand, is an absolute measurement device — It is measuring the light that hits a series of sensor, but the sensor is ‘dumb’, and the signals recorded need to be adjusted to suit the color temperature of the light illuminating the scene, for example

  • Lens focus: In camera, the lens moves closer/further from the film to focus. In your eyes, the lens changes shape to focus: The muscles in your eyes change the actual shape of the lens inside your eyes.

  • Sensitivity to light: A film in a camera is uniformly sensitive to light. The human retina is not. Therefore, with respect to quality of image and capturing power, our eyes have a greater sensitivity in dark locations than a typical camera.

    There are lighting situations that a current digital cameras cannot capture easily: The photos will come out blurry, or in a barrage of digital noise. As an example, when observing a fluorescence image of cells under a microscope, the image you can see with your eyes would be nigh-on impossible to capture for an ordinary camera. This is mainly because of the fact that the amount of light entering the camera (and your eyes) is so low.

Ans 3: Answer in the image.

Ans 4: Object Space or Local space

Local space is the coordinate space that is local to your object, i.e. where your object begins in. Imagine that you've created your cube in a modeling software package (like Blender). The origin of your cube is probably at (0,0,0) even though your cube might end up at a different location in your final application. Probably all the models you've created all have (0,0,0) as their initial position. All the vertices of your model are therefore in local space: they are all local to your object.

The vertices of the container we've been using were specified as coordinates between -0.5 and 0.5 with 0.0 as its origin. These are local coordinates.
Ans 5: World space

If we would import all our objects directly in the application they would probably all be somewhere positioned inside each other at the world's origin of (0,0,0) which is not what we want. We want to define a position for each object to position them inside a larger world. The coordinates in world space are exactly what they sound like: the coordinates of all your vertices relative to a (game) world. This is the coordinate space where you want your objects transformed to in such a way that they're all scattered around the place (preferably in a realistic fashion). The coordinates of your object are transformed from local to world space; this is accomplished with the model matrix.
Ans 6: Answer in image.
Ans 7: (Further adding to Ans 5) : The model matrix is a transformation matrix that translates, scales and/or rotates your object to place it in the world at a location/orientation they belong to. Think of it as transforming a house by scaling it down (it was a bit too large in local space), translating it to a suburbia town and rotating it a bit to the left on the y-axis so that it neatly fits with the neighboring houses. You could think of the matrix in the previous chapter to position the container all over the scene as a sort of model matrix as well; we transformed the local coordinates of the container to some different place in the scene/world.
Ans 8: Projection & it's types: It is the process of converting a 3D object into a 2D object. It is also defined as mapping or transformation of the object in projection plane or view plane. The view plane is displayed surface.
(Types in the image).
Ans 9:  Orthographic vs Perspective Projection:
Orthographic projections are parallel projections. Each line that is originally parallel will be parallel after this transformation. The orthographic projection can be represented by a affine transformation.

In contrast a perspective projection is not a parallel projection and originally parallel lines will no longer be parallel after this operation. Thus perspective projection can not be done by a affine transform.
Ans 10: Look-At
The Graphics Rendering Pipeline • Rendering is the conversion of a scene into an image: Render 3D Scene 2D Image • The scene composed of models in three space. Models, composed of primitives, supported by the rendering system. • Models entered by hand or created by a program. For our purposes today, models already generated. • The image drawn on monitor, printed on laser printer, or written to a raster in memory or a file. These different possibities require us to consider device independence. • Classically, "model" to "scene" to ''image" conversion broken into finer steps, called the graphics pipeline. Commonly implemented in graphics hardware to get interactive speeds. • At a high level, the graphics pipeline usually looks like Modelling Transformatos Model Viewing Transformations Jo stan CIDE MZ 3D World Scene 3D View Scene M3 Model (VCS) (WCS) (MCS) Protection Rasterizados 20-0 Normalize clip 2D/3D Device Scene 0- 2D Image (NDCS) (DCS or SCS)

Synthetic camera model: Each point in the 3D model is projected onto the image plane using the pin-hole camera model

3D-Viewing-Pipeline The viewing-pipeline in 3 dimensions is almost the same as the 2D-viewing-pipeline. Only after the definition of the viewing direction and orientation (1.e., of the camera) an additional projection step is done, which is the reduction of 3D-data onto a projection plane: nom. object- coord. Creation of objects and scenes world-Definition of viewing. Projection proj.- coord mapping region coord onto image coord. image coord. + orientation plane Mapping on unity image region device. coord. Transform. to specific device device coord This projection step can be arbitrarily complex, depending on which 3D-viewing concepts should be used. Viewing-Coordinates Similar to photography there are certain degrees of freedom when specifying the camera: 1. Camera position in space 2. Viewing direction from this position world- 3. Orientation of the camera (view-up vector) coordinates 4. Size of the display window (corresponds to the focal length of a photo-camera) viewing- With these parameters the camera-coordinate system is coordinates defined (viewing coordinates). Usually the xy-plane of this viewing-coordinate system is orthogonal to the main viewing direction and the viewing direction is in the direction of the negative z-axis. Based on the camera position the usual way to define the viewing-coordinate system is: 1. Choose a camera position (also called eye-point, or view-point). 2. Choose a viewing direction = Choose the z direction of the viewing-coordinates. 3. Choose a direction „upwards". From this, the x-axis and y-axis can be calculated: the image-plane is orthogonal to the viewing direction. The parallel projection of the view-up vector“ onto this image plane defines the y-axis of the viewing coordinates. 4. Calculate the x-axis as vector-product of the 2- and y-axis. 5. The distance of the image-plane from the eye-point defines the viewing angle, which is the size of the scene to be displayed. In animations the camera-definition is often automatically calculated according to certain conditions, e.g. when the camera moves around an object or in flight-simulations, such that desired effects can be achieved in an uncomplicated way. To convert world-coordinates to viewing-coordinates a series of simple transformations is needed: mainly a translation of the coordinate origins onto each other and afterwards 3 rotations, such that the coordinate-axes also coincide (two rotations for the first axis, one for the second axis, and the third axis is already correct then). Of course, all these transformations can be merged by multiplication into one matrix, which yw + V yw looks about like this: YvVzy . Yw Mwc,vc=R_R:RI

Three-dimensional Viewing Pipeline World coordinates (3D) transform Transform into view coordinates and Canonical view volume View coordinates(3D) clip Clip against canonical view volume View coordinates(3D) Project on to view plane View coordinates (2D) transform Map into viewport Normalized device coordinates Transform to physical Device coordinates Physical device coordinates

Types of Projection Projection Parallel Perspective Orthographic Oblique One Point Two Point Three Point General Multiview Axonometric Cavalier Cabiner Isometric Dimetric Trimetric
The idea of the method is simple. In order to set a camera position and orientation, all you really need is a point to set the camera position in space which we will refer to as the from point, and a point that defines what the camera is looking at. We will refer to this point as the to point.