Template:Maya2017 modeling polygons theory
Introduction
The objects we create in Maya, like real objects, have certain properties which define their possible use. It can be compared with the different use of cardboard, MDF or clay in making a physical model. Each material has its own properties, ways how to modify it and the forms you can create with it. You would not use a saw on clay and you would not use MDF to make a model with a double curved surfaces. If we want to design in the computer we will have to know the properties of the geometry we use in the design process. It will define what kind of form can be generated, the possibilities of altering the form and the accuracy of the form ( interesting if you want to digitally manufacture the object).
We will use polygons for the first two workshops.
Polygon is a straight forward description of geometry in 3D. The polygon is a very simple description of geometry. Its form is defined by a set of coordinate points (vertices). A set of coordinate points are maybe interesting for the computer to work with, we only see a lot of dots. To make the form visible they added between each three points a triangular surface, which is called a face. These faces together between all the coordinate points are what we are seeing. This structure has a substantial influence on what you can do with the geometry.
- The shape is defined by its coordinate point or vertices. The vertices will define the shape of the geometry
- The surface of the geometry is defined by the planar triangular faces. The faces will define the surface of the geometry
- The edges of the geometry are the edges of the faces. The edge is always a straight line
Advantages:
- Possibility of describing volumes
- Less memory intensive
- Straight forward mathematical description
- Commonly used geometry type
Disadvantage:
- The curvature is only approximated by the face between the vertices
- High poly count necessary for curved shapes approximation
Applications:
- Modelling Cartesian architecture
- Architectural visualisation
- Architectural interactive virtual visualisation
- Geometry for analysis
- Geometry for Rapid Prototyping
The straight forward description of the polygon as a set of coordinate points makes it especially suitable for analysis and rapid prototyping. Distances, areas, volumes and angles can be calculated based on the position of the coordinate points. The low memory requirement for display makes polygons the favourite geometry for virtual reality environments like web based interactive virtual environment and games. The possibility of generating volumes makes polygons faster in modeling of straight angled surfaces
The disadvantage of not being able to describe curved surface accurately is a major drawback in designing with polygons. Because there is always a straight edge between two coordinate points (vertices) the curvature will always be a crude approximation. This one of the reasons polygons are not used in more complex designs with curved ore double curved surfaces.
The geometry
If you want to design in the computer you will have to know the properties of your design environment, its possibilities and its limitation. Not only the geometry type is of influence on the design process. Polygons for example have the problem of not being able to accurately describe curved surfaces. The form you start to design with is also of influence on the possibilities of generating a formal description of your design. There are 3 different kind of geometry forms you can start from.
The first one is the volume or predefined volumes ( primitives). If we start using volumes as a basis for modeling our design we have the advantage that the geometry is already defined in 3 dimensions. We can alter our 3D geometry by deforming it ( make a cube into a rectangular box) or making a combination of different kind of 3D objects ( subtracting one box from the other to create a hole) This starting form however has its limitations because the 3 dimensions are already defined from the start. The topology , organization of the surfaces, of the form predefined. Although complex objects can be made with this kind of geometry it can be quite difficult.
The second more flexible geometry to start with is the surface. If we can generate a surface, we can define its form in two dimensions. By extruding the form in the third dimension we can generate a 3 dimensional object. This extrusion process however is often limited to a simple straight extrusion. So the influence on the 3rd dimension is limited. The maximum freedom in this case is primarily limited to two dimensions. This makes this form especially suitable for geometry with a complex section and a simple extrusion, like a facade or a steel beam.
The third option is the most flexible and is widely used in digital design. In this case the basic form is a line or a combination of lines. The strength of the use of lines as a start for geometry is the fact that the line not only can define a surface in two dimensions ( a complex surface ) but by using a combination of lines the third dimension can also be defined by a line. This method of constructing complex geometry with the help of lines is called curved based modeling and is widely used in other industries like product design, car design and in the aero-space industry.
In this course we will use all the three techniques. We will start with the creation of volumes and the techniques how to modify them.
