GiD is a CAD system that features the widely used NURBS surfaces (trimmed or not) for the geometry definition. Typicall geometrical operations can be used as transformations (translations, rotations, etc.), boolean operations in surfaces and volumes. A complete set of tools are provided for quick geometry definition.

• CAD geometrical data can be read in DXF, VDA, IGES, STL, Shapefile, Parasolid, ACIS and Rhino formats.
• Mesh data can be read in NASTRAN, STL, VRML, 3dStudio, CGNS, VTK, formats.
• Exportation of geometrical data can be done in IGES, ACIS, DXF or Rhino format.
• Several mesh analysis (mesh) data can be exported using a template file.

Several automatic CAD cleaning operations are made when importing a geometrical CAD model following certain tolerances. There are a handful of graphical tools to detect and repair geometry, allowing the generation of a proper mesh to run a simulation. Different kinds of NURBS simplification algorithms are available to improve the efficiency of the geometrical definition.

GiD allows the generation of large meshes (for linear and quadratic elements) in a fast and efficient manner using several in-house meshers, both for surfaces and volumes, following different structured type criteria:

• Structured mesher including triangular, quadrilateral, hexahedral, prism and tetrahedral meshes.

• Unstructured meshes are automatically generated based on quality and spacing criteria defined by the user (or using a background mesh for defining a certain size distribution). Several element types can be generated: triangular, quadrilateral, circles, spheres and tetrahedral.

Three unstructured surface meshers available for generating triangle or quadrilateral. They are based in advancing front technique:

• RFAST: generate the mesh in the surface parametric space (2D), and afterwards mapp the resulting mesh in the three-dimensional space. Mesh is generated faster, but the quality of the resulting mesh may be not so good in some cases.

• RSURF: generates the mesh directly in the space (3D). It is slower than RFAST, but it gives a better quality meshes.

• RJUMP: generates the mesh in space (3D) of a group of surfaces, skipping the contact lines between surfaces, following certain criteria: tangency between neighbour surfaces, lines selected by the user or continuity between surfaces curvatures.

Three unstructured volume meshers for tetrahedra are available:

• Based in advancing front technique.

• Based in Delaunay technique.

• Based in Isosurface algorithm.

• Semi-structured volume meshes (structured in one direction of a topollogicaly prismatic volume) of hexahedra, prisms or tetrahera.

• Cartesian meshes of hexahedra.

GiD also can generate 2D and 3D anisotropic meshes (usefull for boundary layer).
Several mesh editing tools like edge collapsing, elements splitting, smoothing, etc. allow the user to have the total control of any kind of mesh.

Now GiD contains tools to convert any mesh model to a NURBS surfaces model, this implies big advantages and a large amount of freedom with editing, meshing and running any kind of simulation.

Simple assignment of any kind of data to the geometry and/or the mesh (boundary conditions, material properties, etc.). This information can be sent to the solver with other analysis data, which is easily included because of GiD customization.