Wire-frame model

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A wire-frame model is a visual presentation of a 3-dimensional (3D) or physical object used in 3D computer graphics. It is created by specifying each edge of the physical object where two mathematically continuous smooth surfaces meet, or by connecting an object's constituent vertices using straight lines or curves. The object is projected into screen space by drawing lines at the location of each edge. The term wire frame comes from designers using metal wire to represent the three-dimensional shape of solid objects. 3D wire frame allows to construct and manipulate solids and solid surfaces. The 3D solid modeling technique efficiently draws higher quality representations of solids than the conventional line drawing.

Using a wire-frame model allows visualization of the underlying design structure of a 3D model. Traditional two-dimensional views and drawings can be created by appropriate rotation of the object and selection of hidden line removal via cutting planes.

Since wire-frame renderings are relatively simple and fast to calculate, they are often used in cases where a high screen frame rate is needed (for instance, when working with a particularly complex 3D model, or in real-time systems that model exterior phenomena). When greater graphical detail is desired, surface textures can be added automatically after completion of the initial rendering of the wire frame. This allows the designer to quickly review solids or rotate the object to new desired views without long delays associated with more realistic rendering.

The wire frame format is also well suited and widely used in programming tool paths for direct numerical control (DNC) machine tools.

Hand-drawn wire-frame-like illustrations date back as far as the Italian Renaissance. Wire-frame models were also used extensively in video games to represent 3D objects during the 1980s and early 1990s when properly filled 3D objects would have been too complex to calculate and draw with the computers of the time. Wire-frame models are also used as the input for computer-aided manufacturing (CAM).

There are mainly three types of 3D CAD models. Wire frame is one of them and it is the most abstract and least realistic. Other types of 3D CAD models are surface and solid. This method of modelling consists of only lines, points and curves defining the edges of an object.

Video Wire-frame model

Introduction

Wireframing is one of the methods used in geometric modelling systems. A wireframe model represents the shape of a solid object with its characteristic lines and points. There are two types of wireframe modelling: Pro's and Con's. In Pro's user gives a simple input to create a shape. It is useful in developing systems. While in Con's wireframe model, it does not include information about inside and outside boundary surfaces. Today, wireframe models are used to define complex solid objects. The designer makes a wireframe model of a solid object, and then the CAD operator reconstructs the object, including detailed analysis. This technique has some advantages: generally the 3-dimensional solid objects are complex, but wireframe models can be viewed in 1 dimension, improving comprehensibility; the solid object can be modified further; the designer can ignore the geometry inside a surface while in solid modelling the designer has to give consistent geometry for all details; wireframe models require less memory space and CPU capacity.

Maps Wire-frame model

Simple example of wireframe model

An object is specified by two tables: (1) Vertex Table, and, (2) Edge Table.

The vertex table consists of three-dimensional coordinate values for each vertex with reference to the origin.

Edge table specifies the start and end vertices for each edge.

A naive interpretation could create a wire-frame representation by simply drawing straight lines between the screen coordinates of the appropriate vertices using the edge list.

Unlike representations designed for more detailed rendering, face information is not specified (it must be calculated if required for solid rendering).

Appropriate calculations have to be performed to transform the 3D coordinates of the vertices into 2D screen coordinates.

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See also

• 3D computer graphics
• Animation
• Computer animation
• Computer-generated imagery (CGI)
• Mockup
• Polygon mesh
• Vector graphics
• Virtual cinematography

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References

1. Principles of Engineering Graphics by Maxwell Macmillan International Editions
2. ASME Engineer's Data Book by Clifford Matthews
3. Engineering Drawing by N.D. Bhatt
4. Texturing and Modeling by Davis S. Ebert
5. 3D Computer Graphics by Alan Watt

Source of the article : Wikipedia