A polygon mesh is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling. The faces usually consist of triangles, quadrilaterals or other simple convex polygons.
Although it is possible to construct a mesh by manually specifying vertices and faces, it is much more common to build meshes using a variety of tools and techniques. A wide variety of 3d graphics software packages are available for use in constructing polygon meshes.
Primitive Modelling
1) In computer programming, a primitive (pronounced PRIH-muh-teev ) is a basic interface or segment of code that can be used to build more sophisticated program elements or interfaces.
2) In computer graphics, a primitive is an image element, such as an arc, a square, or a cone, from which more complicated images can be constructed.
Cubes
Pyramids
Cylinders
Spheres
2D primitives, such as squares, triangles, and disks
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Box Modelling
Box modeling is a technique in 3D modeling where a primitive shape (such as a box, cylinder, sphere, etc.) is used to make the basic shape of the final model. This basic shape is then used to sculpt out the final model. The process uses a number of repetitive steps to reach the final product, which can lead to a more efficient and more controlled modelling process.
Extrusion Modelling
Extrusion is a method of adding geometry to a polygon primitive, and one of the primary tools a modeler uses to begin shaping a mesh.
Through extrusion a modeler manipulates the 3D mesh by either collapsing a face in upon itself (to create an indentation), or by extruding the face outward along its surface normal—the directional vector perpendicular to the polygonal face.
Extruding a quadrilateral face creates four new polygons to bridge the gap between its starting and ending position. Extrusion can be difficult to visualize without a concrete example:
- Consider a simple pyramid shape, with a quadrilateral (4-edged) base. A modeler might transform this primitive pyramid into a house-like shape by selecting the base of the pyramid and extruding it in the negative Y direction. The pyramid's base is shifted downward, and four new vertical faces are created in the space between the base and the cap. A similar example might be seen in modeling the legs of a table or chair.
- Edges can also be extruded. When extruding an edge, it is essentially duplicated—the duplicate edge can then be pulled or rotated away from the original in any direction, with a new polygonal face automatically created connecting the two. This is the primary means for shaping geometry in the contour modeling process.
- http://3d.about.com/od/Creating-3D-The-CG-Pipeline/tp/Polygonal-3d-Modeling-Common-Box-And-Edge-Modeling-Workflows.htm
Sketch Modelling
sketch-based modeling is a method of creating 3D models for use in 3D computer graphics applications. Sketch-based modeling is differentiated from other types of 3D modeling by its interface - instead of creating a 3D model by directly editing polygons, the user draws a 2D shape which is converted to 3D automatically by the application.
3D Scanners
A 3D scanner is a device that analyses a real-world object or environment to collect data on its shape and possibly its appearance (e.g. colour). The collected data can then be used to construct digital three-dimensional models.
Many different technologies can be used to build these 3D-scanning devices; each technology comes with its own limitations, advantages and costs. Many limitations in the kind of objects that can be digitised are still present, for example, optical technologies encounter many difficulties with shiny, mirroring or transparent objects. For example, industrial computed tomography scanning can be used to construct digital 3D models, applying non-destructive testing.
Collected 3D data is useful for a wide variety of applications. These devices are used extensively by the entertainment industry in the production of movies and video games. Other common applications of this technology include industrial design, orthotics and prosthetics, reverse engineering and prototyping, quality control/inspection and documentation of cultural artifacts.
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