Generative modeling is founded on the idea that a wide variety of mathematical operators, including constraint solution, differentiation, integration and more traditional modeling operators of hierarchical transformations and constructive solid geometry, form a natural language for shape specification. To this end, generative modeling offers a mathematically closed set of operators made up of the standard hierarchical operations for rigid objects (push, pop, rotate, translate, name object, etc.), constructive solid geometry operations (intersection, union, subtraction), and operators for creating time-dependent surfaces and other shapes (such as sweep operators, differentiation, integration, inverse functions, constraint solution, constrained minimization).

These operators are all made robust using the powerful mathematical technique of interval analysis, and provide a rich architecture and environment in which to base a modeling system. Details of this work have been published in a 1992 SIGGRAPH paper and John Snyder's 1992 Book .

Because of design philosophy of mathematical closure under the generative modeling operators, it is possible to create parameterized models in which the designer can have direct control over the specific degrees of freedom which are applicable. It is also possible to define objects which vary over time (e.g. objects which have time as a geometric parameter), to create objects imbedded in other spaces (such as density functions on volumes or vector fields on surfaces), or to specify objects as the solutions to specific mathematical equations, such as differential, integral, or constrained optimization equations.

Newgen uses and interpreted extension of the C language called cinterp as its environment for specifying the shape functions, and includes a curve editor for specifying curves by interactive design. It can also create models from implicit functions and extract them from volume datasets, such as MRI images.

An important element of the design philosophy of newgen is the idea that the user should be able to see the shape in full detail during the design stages. Therefore, newgen provides a viewing system which allows interactive examination in a continuous, real-time polygonal representation with interactively-controlled sampling resolution and rendering properties.

Newgen has been used as the geometric, and often the mathematical,
interface for several raytracers and physical simulators, and to
produce the short animated movies
Fruit Tracing (1993)
and
Going Bananas (1987).
**Newgen** is available for HP9000 series 700 workstations via
FTP .

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Last modified: 27 Dec 1994

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