In GOCAD Mallet (1993), a model is a set of domains bounded by interfaces (triangulated surfaces) and in which some properties are defined such as velocities, porosities, permeabilities, and densities. These properties can be constant and attached to a whole domain or variable and computed at each point inside the domain.

Figure 1 shows a 2-D slice of such a model composed of six
domains delimited by their boundaries. Each boundary is characterized by an
interface and a side (+ or -). On the same page lies an excerpt of an
example of a file used in GOCAD to describe the partition of the 3-D space
associated with the set of interfaces. For example, the domain named
`Domain_4` is defined by the boundary `S2-`, `F-`, and `S3+`,
and the properties available in this domain are a constant velocity
(2700.0 m/s) and a function named `density( input1, output1)` giving the
density of the layer (ouput1) with respect to some parameters (input1). In the
GOCAD library, there are functions to retrieve the properties attached to a
domain from the location of a point in the 3-D space.

11/17/1997