Maxsurf supports IGES entities, which allow you to transfer an exact surface description from Maxsurf, if you use a high end CAD system, such as Intergraph EMS, which supports B-spline surfaces. This is the most advanced and accurate way to transfer the model and ensures that accuracy is preserved. Use the Export function to export an IGES NURBS surface model in 3D. When your CAD system reads in the data it will accept the surfaces and will then allow you to manipulate them in any way that the system allows.

As well as the usual contours, which are saved as IGES entity number 106, Maxsurf will save an IGES entity number 128 for each Maxsurf surface and any associated trimming data as entity 144. This entity is a NURB (Non Uniform Rational B-spline) surface, which has the positions of the control points and the stiffness of the surface stored within it.

If you wish to write custom software that needs to read accurate Maxsurf surface descriptions, we recommend that you support input of the IGES file and this entity in particular as the most effective way of accessing the Maxsurf surface description.

Please note that there are some surface topologies that may cause difficulties when they are exported as trimmed IGES surfaces. In these cases the trimming may have to be re-done in the importing application. In most cases the trimmed IGES export should work correctly: For example the topology shown below with multiple edge and interior trims, including intersecting trim regions, will work correctly.

There are two cases where IGES NURBS surface trimming is known to break down. The topology shown below (right), where a trim region contains an untrimmed region, will display correctly in Maxsurf but may not transfer correctly through IGES – this may be dependent on the receiving program.

The major limitation of IGES NURBS transfer is in the interpretation of a surface that has been divided into two or more independent regions, as in the following examples: