5 3d Objects Representation

Computer Graphics · Unit 5 · 7 hrs

3D Objects Representation

Exam-focused notes for 3D Objects Representation (Computer Graphics, CSC214): what the TU syllabus asks and how it has actually been tested, with 13 solved past questions from this unit.

What this unit covers

  • Representing Surfaces: Boundary and Space partitioning
  • Polygon Surface: Polygon tables, Surface normal and Spatial orientation of surfaces, Plane equations, Polygon meshes
  • Wireframe Representation
  • Blobby Objects
  • Representing Curves: Parametric Cubic Curves, Spline Representation, Cubic spline interpolation, Hermite Curves, Bezier and B-spline Curve and surface
  • Quadric Surface: Sphere and Ellipsoid

Representing Curves

20815 marks

Construct the Bezier curve with the following polygon vertices (control points): A(1,1), B(2,3), C(4,3), and D(6,4). [5]

Control points (4 points → cubic Bezier, degree $n = 3$): - $P0 = A(1, 1)$ - $P1 = B(2, 3)$ - $P2 = C(4, 3)$ - $P3 = D(6, 4)$ $$P(u) = \sum{k=0}^{3} Pk \, BEZ{k,3}(u), \quad 0 \le u \le 1$$ $$BEZ{k,3}(u) = \binom{3}{k} u^k (1-u)^{3-k}$$ $k$ Blending Functio...

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20795 marks

Explain about parametric curve. Describe the properties of Bezier curve. [5]

--- A curve is an infinitely large set of points. Curves are broadly classified into three categories: explicit, implicit, and parametric curves. Curves having parametric form are called parametric curves. A two-dimensional parametric curve has the followin...

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20785 marks

Discuss the strength and weakness of the human visual system. Describe Spline representation for the curve. [5]

--- (Standard CS/Graphics knowledge, Do not cover this topic directly.) Strength ------------- 1 Wide dynamic range: The human eye can adapt to a very large range of light intensities, from bright sunlight to dim moonlight. 2 Color perception: The eye can d...

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20785 marks

Define fractal. Explain the Bezier curve and B-Spline curve. [5]

--- A fractal is a geometric figure or natural phenomenon that exhibits self-similarity at every scale of magnification. This means a fractal looks similar (or identical) when zoomed in or out at any level. Fractals are used in computer graphics to model co...

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20755 marks

Mention any two color command in OpenGL. Explain about Hermite curve. [5]

--- OpenGL provides color commands primarily in RGBA mode, where colors are specified using Red, Green, Blue, and optionally Alpha (transparency) components mapped onto the range (0.0, 1.0). This command specifies a color using three floating-point values f...

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Polygon Surface

20805 marks

Explain polygon surface representation using Polygon table and polygon meshes. [5]

The most commonly used boundary representation for a 3D graphics object is a set of surface polygons that enclose the interior of the object. Many graphics systems store all object descriptions as a set of surface polygons because this simplifies and speeds...

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20795 marks

What is polygon table? Explain the use of this method in 3D object representation. [5]

A polygon table is a data structure used to store and organize all the geometric and attribute information about the surface polygons that make up a 3D object. Since the most commonly used boundary representation (B-rep) for a 3D graphics object is a set of...

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20785 marks

What is the task of a polygon table? Why do we have to remove hidden surfaces? Explain with any one methodology. [5]

--- A polygon table is the specification of polygon surfaces using vertex coordinates and other attributes. It organizes the geometric and qualitative data needed to describe a 3D object. Polygon tables are organized into two groups: Three lists are maintai...

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207710 marks

How polygon table is used in representing polygons? Explain the representations of any three curves.[10]

--- The most commonly used boundary representation (B-rep) for a 3D graphics object is a set of surface polygons that enclose the interior of the object. Many graphics systems store all object descriptions as a set of surface polygons because it simplifies ...

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Blobby Objects

20795 marks

What are blobby objects? How it is represented? Explain the wireframe representation of 3D objects. [5]

--- Definition: Objects that do not maintain a fixed shape but change their surface characteristics in certain motions are known as blobby objects. Examples: - Molecular structures - Water droplets - Melting objects - Soft organic shapes (muscles, clouds) T...

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20775 marks

Define blobby objects. Describe about basic illumination models. [5]

--- Blobby objects are objects that do not maintain a fixed shape but change their surface characteristics during certain motions or interactions. Examples: - Molecular structures - Water droplets - Melting objects - Muscle tissue deformation Several models...

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Quadric Surface

20785 marks

What is quadric surface? Compare between diffuse reflection and specular reflection. [5]

--- A quadric surface is a frequently used class of 3D objects described by second-degree (quadratic) equations. These surfaces are defined mathematically using polynomials of degree two in x, y, and z. Common examples of quadric surfaces include: - Spheres...

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Wireframe Representation

20755 marks

What is the purpose of wireframe representation? Describe about boundary and space partitioning. [5]

A wireframe model represents a 3D object by describing only its edges and vertices (corners). It is the simplest form of 3D object representation. Purposes: - To provide a quick and simple visual outline of a 3D object using only its edges and corner points...

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