subject: The 3D Objects and basic elements [print this page] The 3D Objects and basic elements The 3D Objects and basic elements
After a short preface, we can start to get down to specifics, analyzing the modelling matter that is the process used to create objects. Anyway, before to speak about the matter, it's necessary say few words about creation of the model.
We start saying that it's no possible to have an exact distinction between different methods of production, because very often these methods are different at the beginning and similar at the end, when You put the finishing touches and finalize. In this way, user can interact with the software. Anyway, we'll see better the matter during the other lessons, now, we're going to make a forced distinction concerning to the modellings used to create the 3D objects:
- PARAMETRIC MODELLING
- PROCEDURAL MODELLING
- CONTROLLED MODELLING
These categories allow to contain all objects created by putting manual parameters(or not), several features, with (or without) the software and the hardware necessary.
The following objects fall within in these distinctions: primitives, resulting from Boolean operations, objects resulting from spline, objects resulting from extrusion operations and / or revolution, NURBS, polygonal modeling, surfaces of subdivision, deviation maps, 3D scanning, photogrammetry, voxel.
Explaining in details every categories is a process very long and very far from our intention; for this reason, we'll focus about polygonal modelling.Anyway, we going to show you some images concerning objects created by methodologies described.
POLYGONAL MODELLING: BASIC ELEMENTS
What's the polygonal modelling?
We already introduced the matter and we said that it's the best technique to control the creation process, editing and approximating of the the 3D object to the real object. Thanks to this method, the user can check every process concerning to the object, improving some parts if it's necessary.
Before to deepen the matter, we want to explain a very easy but fundamental concept, concerning the 3D. While the 2D software make reference to a two-dimensional system, based on two axes, usually called "X" and "Y", the 3D software consider three axes: "X" and "Y" indicate width and height of an object, while "Z" indicates the depth.
The polygonal modelling follows a system of three-dimensional coordinates; for this reason you can create/modify your object by inserting a value for every dimension. Finally, we can affirm that the polygonal object (mesh) is a projection of the information concerning the three dimensions translated and interpreted from the software.
The basic information/element concerning polygonal modelling is the "polygon" made by some fundamental elements: vertices, edges, faces, normals:
- vertex is a point in the 3D space;
- edge is an element linking two vertices;
- face is a planar elementclosedat least in three edges;
- normal is the perpendicular vector to the face.
We could say that a polygon is characterized by a set of planar faces and normals whose direction allows to the 3D software to change visibility/ shade of the elements.
Concluding, linking many basic elements (or polygons), you can build the polygonal mesh; for this reason, your 3D object will be more detailed as much information as you insert.
