5.1.3 Surfaces

Plane Surface ( expression ) = { expression-list };

Creates a plane surface. The expression inside the parentheses is the plane surface’s identification number; the expression-list on the right hand side should contain the identification numbers of all the line loops defining the surface. The first line loop defines the exterior boundary of the surface; all other line loops define holes in the surface. A line loop defining a hole should not have any lines in common with the exterior line loop (in which case it is not a hole, and the two surfaces should be defined separately). Likewise, a line loop defining a hole should not have any lines in common with another line loop defining a hole in the same surface (in which case the two line loops should be combined).

Ruled Surface ( expression ) = { expression-list } < In Sphere { expression } >;

Creates a ruled surface, i.e., a surface that can be interpolated using transfinite interpolation. The expression inside the parentheses is the ruled surface’s identification number; the first expression-list on the right hand side should contain the identification number of a line loop composed of either three or four elementary lines. The optional In Sphere argument forces the surface to be a spherical patch (the extra parameter gives the identification number of the center of the sphere).

Surface Loop ( expression ) = { expression-list };

Creates a surface loop (a shell). The expression inside the parentheses is the surface loop’s identification number; the expression-list on the right hand side should contain the identification numbers of all the elementary surfaces that constitute the surface loop. A surface loop must always represent a closed shell, and the elementary surfaces should be oriented consistently (using negative identification numbers to specify reverse orientation). (Surface loops are used to create volumes: see Volumes.)

Compound Surface ( expression ) = { expression-list } < Boundary { { expression-list }, { expression-list }, { expression-list }, { expression-list } } > ;

Creates a compound surface from several elementary surfaces. When meshed, a compound surface will be reparametrized as a single surface, whose mesh can thus cross internal boundaries. Compound surfaces are mostly useful for remeshing discrete models; see “J.-F. Remacle, C. Geuzaine, G. Compere and E. Marchandise, High Quality Surface Remeshing Using Harmonic Maps, International Journal for Numerical Methods in Engineering, 2009” for details as well as the wiki for more examples. The expression inside the parentheses is the compound surface’s identification number; the mandatory expression-list on the right hand side contains the identification number of the elementary surfaces that should be reparametrized as a single surface.

Physical Surface ( expression | char-expression ) = { expression-list };

Creates a physical surface. The expression inside the parentheses is the physical surface’s identification number (if a char-expression is given instead, a unique identification number is automatically created); the expression-list on the right hand side should contain the identification numbers of all the elementary surfaces that need to be grouped inside the physical surface. Specifying negative identification numbers in the expression-list will reverse the orientation of the mesh elements belonging to the corresponding elementary surfaces in the saved mesh.

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