In 3D computer graphics, polygonal modeling is an approach for modeling objects by representing or approximating their surfaces using polygons. Polygonal modeling is well suited to scan-line rendering and is therefore the method of choice for real-time computer graphics. Alternate methods of representing 3D objects include NURBS surfaces, subdivision surfaces, and equation-based representations used in ray tracers.
https://en.wikipedia.org/wiki/Polygonal_modeling
Primitive Modelling:
The term geometric primitive in computer graphics and CAD systems is used in various senses, with the common meaning of the simplest geometric objects that the system can handle. Sometimes the subroutines that draw the corresponding objects are called "geometric primitives" as well. The most "primitive" primitives are point and straight line segment, which were all that early vector graphics systems had. A common method of creating a polygonal mesh is by connecting together various primitives, which are predefined polygonal meshes created by the modelling environment.
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.
Quads
Quadrilateral faces, commonly named "quads", are the fundamental entity in box modeling. If an artist were to start with a cube, the artist would have six quad faces to work with before extrusion. While most applications for three-dimensional art provide abilities for faces up to any size, results are often more predictable and consistent when working with quads. This is so because if one were to draw an X connecting the corner vertices of a quad, the surface normal is nearly always the same. We say nearly because, when a quad is something other than a perfect parallelogram (such as a rhombus or trapezoid), the surface normal would be different. Also, a quad subdivides into two or four triangles cleanly, making it easier to prepare the model for software that can only handle triangles.
Subdivision Modelling
https://en.wikipedia.org/wiki/Box_modeling
Extrusion Modelling
This is a common modelling method that is also sometimes referred to as inflation modeling. In this method of modeling, you could create a 2D shape which traces the outline of a photograph or a drawing. This would be done more commonly using the line tool, because of its simplicity and because it is so easy to work with and create things with it. You then use a second image of the subject from a different angle and extrudes the 2D shape into a 3D shape by following the shape’s outline again. This method is common for creating faces and heads in modeling, and artists will generally model half of the head and duplicate the vertices, invert their location relative to a plane and connect the two pieces to ensure that the model would then be symmetrical. This method is widely used by 3D artists because of it being so practical, quick and simple.
https://jessgrafton.wordpress.com/3d/mesh-construction/
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.
https://en.wikipedia.org/wiki/Sketch-based_modeling
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.
https://en.wikipedia.org/wiki/3D_scanner
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