To convert from one format to another, Interchange loads data into an internal database, then converts this data to the format selected in the Converters list. By understanding the way Interchange represents 3D data, you'll know what to expect when converting from one format to another.

The Interchange database represents polygonal geometry with material attributes. The database itself has a name that corresponds to a "scene name" in some 3D file formats. It also has a list of materials used to color the polygons.

Most importantly, the database contains objects composed of points, edges, and polygons. Each object has a name, a center point, and a description of its relationship in a hierarchy. Each object can have an unlimited number of points, edges and polygons. The actual limit is about 4 billion of anything - materials, points, edges and polygons, but few personal computers have enough memory to represent a model this large. Each polygon in a object can have up to 65,535 sides. For its color and other material attributes, each polygon references one of the database's materials.

Although Interchange's internal database can accommodate objects with a large number of points and polygons, your actual limit is the amount of memory in your machine or the limits of a particular modeling program. Even if Interchange can convert a particular object, you might not be able to load or render the object in the same amount of memory. Editing and rendering an object often requires much more memory than converting an object with Interchange.

Material attributes
Each Interchange material has a descriptive name such as "Shiny Blue Plastic". The name can be as long as 64 characters. When exporting, material names are adjusted according to the requirements of the destination format, such as shortening the name or replacing illegal characters.

Material colors and other attributes are stored as floating point values, allowing precise conversion to and from 24-bit RGB systems. The material definition includes the basic diffuse color, ambient and specular colors, a filter color and emissive color. The diffuse color is almost always set, the others are optional.

The material definition also includes values (also known as coefficients) that interact with the above colors. The diffuse coefficient sets the amount of ambient light that the material reflects. The specular coefficient sets the relative size of the specular highlights, while the glossiness value controls how "shiny" or "hard" or "soft" that specular reflection looks.

The index of refraction controls how much light will bend when passing through the object. This value is most often used in ray-tracing programs that can make glass-like objects.

The smoothing angle sets the angle used by each program's auto-smoothing function.

Also, each material can be flagged as luminous, wireframe, double-sided and smooth. Luminous materials are not shaded or otherwise affected by light sources, and are often used to give the effect of a neon sign. The material's luminosity can be set as a percentage.

With wireframe polygons, only the outline is drawn with the diffuse color. Not all programs support the wireframe attribute. Polygons with double-sided materials are visible from both sides.

Smooth polygons are drawn with no hard-edge border connecting them to other smooth. Interchange preserves the smoothing material attribute, although a perfect match between programs is not always possible because of the many different techniques to alter and control smoothing.

For example, some programs have only a simple smoothing flag and re-compute the smoothing normals at render time based on the angle between polygons and whether those polygons are actually adjacent or not, while other programs give detailed control over the shared points and normals within polygons.

Texture maps
Most programs allow bitmap images to modify a material's attributes. These texture maps can modulate the material's color, shininess and many other aspects of the material. Interchange preserves the notions of diffuse, diffuse coefficient, bump, opacity, environment, ambient, specular, luminosity, refraction, filter, and decal texture maps.

Along with the geometry of a model, Interchange can also translate the texture bitmaps between formats.

For background information about geometry and materials, see the "3D Concepts" chapter.