Modeling 3D

Stage in Computer graphics 3D which consists in creating, in a Logiciel of modeling 3D, an object in three dimensions, by addition, subtraction and modifications of its components.

Polygonal modeling

Polygonal modeling: the model is compared to a whole of polygons: this Polyèdre is thus described by the list of the tops and the edges. If the polygons are directed, one will be able to differentiate the outside and the interior of the model. If one wants to raise the ambiguity brought by nonplane polygons, one will use only triangles: this triangulation can be forced by the modeller.

Without effect of smoothing, the object will appear angular if the definition in facets is weak. In general, the smoothing of Gouraud, realized by the graphics card 3D, is sufficient to give a smoother aspect to the model.

Polygonal modeling makes use of identical basic tools on all the software 3D, like certain tools specific to the generic software, the specialized software and the plug-ins and scripts.

Among these tools, most widespread are extrusion, the cut ( cut , Split …), and the welding/retractation ( weld / collapse ) and the revolution.

The extrusion consists in raising one or more faces (adjacent or not) or a profile 2D along a trajectory and to create the faces coming to fill the vacuum caused by the displacement of the starting element. For example, to extrude a circle an open cylinder or a pipe gives which follows the trajectory.

The cut consists in creating edges ( edges ) on a grid, as well as the points corresponding to the intersections of the already existing edges and those lately created. One can thus refine a model, by adding details on certain areas, in particular by the addition of loops of edges ( edgeloops ) extremely used in organic modeling.

The welding/retractation consists in welding the tops ( vertices ) between them, to simplify a grid, to stop holes or to make converge edges.

The revolution consists in making turn a profile 2D around an axis 3D: a volume of revolution thus is obtained.

It is the technique mainly used in the video game, and the cinema of animation. To note that polygonal modeling induced a margin of error of proportions and dimensions generally invisible with the naked eye. In the cinema of animation, the models 3D organics are generally smoothed. Smoothing consists to subdivide a grid (an iteration corresponds to a subdivision of each edge, that is to say in the case of vis-a-vis four sides, a subdivision in four faces) and to round the faces obtained according to various algorithms, in order to gum the angular effect of the models obtained by polygonal modeling.

Modeling by curves (NURBS)

Modeling by NURBS (Not uniform rational BASIC spline/Spline basic rational not uniform) consists of a network of curves created thanks to check-points ( control vertices ). The interpolation of the curves between these points can be done automatically according to an algorithm NURBS, by handling of tangents of Courbe of Bézier, or by modification of the parameters of interpolation.

Modeling by curve is based on an adaptive grid, conceived to adapt its subdivisions to the complexity of the curves in a given area. A perfectly plane surface will have a number of very low or zero subdivision. It is the technique of the most precise modeling. This is why it is massively used in industrial architecture and CAD, when the preoccupation with a precision precedes (in particular when the models 3D are used as reference for the machine tools).

Modeling by subdivision of surface

This method gathers a little of the two traditional methods (polygonal and NURBS). It consists in accelerating the process thanks to the automatic subdivision of part of surface. This makes it possible to only add details to certain places, without worrying about the number of faces included/understood on globality of the object.

It approaches polygonal modeling by the techniques employed during the creation of the form, and modeling by NURBS with regard to returned surface, i.e. its round-off.

It is present in many professional software (Maya, 3ds max, Lightwave, Softimage…).

See Surface of subdivision

Modeling by implicit surfaces

  • implicit surfaces

Modeling by geometries

Voluminal modeling

Internal bonds

Some software of modeling 3D

See also: Modeller 3D

See too

Computer graphics | Animation | Synthesis of image 3D | Geometry of construction of solids

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