In general terms import means the reading of data. For FEM this data is usually provided in the formats ASCII or binary. Both formats describe a virtual object in two- or three-dimensional space.
By using FEA the virtual object must be simulated through finite (small) elements. For this, mainly simple and well-known geometric shapes are used. These are mostly triangles and rectangles in two-dimensional space or tetrahedrons and hexahedrons in three-dimensional space. In general, the virtual object is defined in its shell shape by straight and curved lines.
This in turn means the replica of the shell shape by finite geometric elements. There are two fundamental approaches to be considered.
The first step of the indirect import is to define the exact shell shape by using straight and curved lines. It is saved in .stp- or .stl-files. These come from CAD (Computer Aided Design). This shell shape must be read and approximately replicated with finite elements. The transformation has already been completed when using direct import and node coordinates and the coincidence list are read in. The coincidence list defines the corner points of the different element types. Ultimately the shell shape and the complete geometry in three-dimensional space are defined through nodes and elements in both approaches. For the following pre-processing the same foundation consisting of node coordinates and the coincidence list is available.