# Geometry

What is the difference between green and magenta colored surfaces, and blue and white solids?

There are two types of surfaces in MSC.Patran:

1. Parameterized ((green) ) surfaces have only 3 or 4 edges. This means that there is a direct mapping of mesh paths between one edge and another. “Parameterized” means that a geometry entity has mesh path parameters inside the surface that the Isomesher will use to create elements.

2. Trimmed (magenta) surfaces can have more than 4 edges and can have interior holes. There is no parameterization inside these type of surfaces. This means that the Isomesher will not be able to mesh this type of surface since they have no mesh paths. Use the Paver mesher to mesh trimmed (magenta) surfaces.

There are two kinds of solids in MSC.Patran:

1. Parameterized (blue) solids have only 5 or 6 faces. Similar to a green surface, this type of solid can be Isomeshed.

2. B-Rep (white) solids can have a more than 5 or 6 faces. “B-Rep” means Boundary Representation. This means that the solid is defined just by its boundary surfaces. A B-Rep solid can only be meshed using the Tetmesher (hence only tet elements) because they do not have any mesh paths defined inside the solid.

The Tetmeshing algorithm works this way:

• It meshes the faces with 2d triangular elements.

• It equivalences to tie all the surface elements together.

• It verifies that all element normals are facing outward.

• It then fills the volume inside with tet elements.