4. Mesh Construction

People who will use Mesh Contruction will often opt to create the mesh using a variety of tools. This includes lots of different software programs that will assist and aid in creating the mesh, opposed to creating the mesh manually by specifying verticies anf faces. 

Box Modelling
Box modeling is a technique in 3D modeling where you take a basic primitive shape (like a box, cylinder or others) and make the basic shape “rough draft” of your final model from there you sculpt out your final model. The process uses various tools and steps that sometimes get repeated again and again until you're done. Despite the fact you’re repeating these steps you will model faster and control the amount of detail you wish to add, slowly building your model up from ground level of detail to high level. 

Quadrilateral faces, commonly named "quads", are the fundamental entity in box modeling. Obviously, 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 of the fact if you were to draw an X connecting the corner vertices of a quad, the surface normal is nearly always the same. We say nearlybecause, 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.

Extrusion Modelling

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 scanline 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. See polygon mesh for a description of how polygonal models are represented and stored.

The basic object used in mesh modeling is a vertex, a point in three dimensional space. Two vertices connected by a straight line become an edge. Three vertices, connected to each other by three edges, define a triangle, which is the simplest polygon in Euclidean space. More complex polygons can be created out of multiple triangles, or as a single object with more than 3 vertices. Four sided polygons (generally referred to as quads) and triangles are the most common shapes used in polygonal modeling. A group of polygons, connected to each other by shared vertices, is generally referred to as an element. Each of the polygons making up an element is called a face.

Primitive Modelling

Another common method of creating a polygonal mesh is by connecting together various primitives, which are predefined polygonal meshes created by the modelling environment. Common primitives include:

Cubes

Pyramids

Cylinders

Spheres

2D primitives, such as squares, triangles, and disks

Specialised Modelling

Finally, some specialized methods of constructing high or low detail meshes exist. Sketch based modeling is a user-friendly interface for constructing low-detail models quickly, while 3d scanners can be used to create high detail meshes based on existing real-world objects in almost automatic way. These devices are very expensive, and are generally only used by researchers and industry professionals but can generate high accuracy sub-millimetric digital representations.