A surface can be defined as the exposed layer of a material
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A surface model is a representation of a surface. A geometric modeller is an instrument used to model a surface.
PowerShape is a geometric modeller with wireframe and surface modelling capabilities. It is suitable for the design and analysis of components with complex shapes and surfaces.
A surface modelled using PowerShape is known as a power surface. You can imagine a power surface to be like a skin with no thickness, placed on a material.
The following figure shows how a power surface can be viewed as a skin. The skin is lifted from the material.
PowerShape can also produce primitive surfaces and surface types compatible with other CAD programs.