IGES Vs STEP: cylinders

See attach.

It is a cube with fillets, constant fillets, same radiuses everywhere.

In the original CAD format, fhe fillets on the edges are actual CYLINDERS.
The fillets on the corners arem portions of spheres.

When I load the data into Draw, I see problems in IGES. It looks like the cylinders are not treated properly (in this case).
STEP format works fine.

I can workaround the problem if I convert to nurbs the cylinders in the original CAD format before saving in IGES. I would say that it is an obvious workaround but it would be much better if we could treat the (trimmed) cylinders within IGES format.

Can anyone make a test and verify it?
Is there any hidden IGES param that I have to activate before loading my file?



Markus Rhein's picture

Hello Davide,

I can confirm with Win 64 Bit, OCC 6.5.0 and standard import parameters there are missing faces after IGES import. The import works correct if you set the read.surfacecurve.mode parameter to the value 3 or -3:


This parameter is described in the IGES format user guide. I also have the problem with some IGES files, that the default parameter for this won´t work and I have to set the import parameter manually to a certain value to enforce usage of 2D or 3D curves respectively. Does anyone know: Is there a automatic way to determine witch parameter should be used?

Hope that helps. I have never used draw so I don´t know how to set the parameter there ...


ciarlond's picture

Many thanks Markus

Can you please send me the iges-out after using the read.surfacecurve.mode parameter to the value 3 or -3

again, thanks


Markus Rhein's picture

Attached is the converted IGES file. The conversion is done by CADExchanger (www.cadexchanger.com/), since I don´t have an export function in my own application. In CADExchanger you can set some of the translation parameters in the GUI (such as read.surfacecurve.mode). CADExchanger uses OpenCASCADE underneath so the output file shouldn´t be much different from OCC XDE, but I can´t say for sure. If you haven´t tried it out yet I would recommend to test CADExchanger for yourself. It is a really helpful tool for CAD data translation.

ciarlond's picture

Thank you very much!

it worked fine: I have CYLINDERS in my system now

Probably that parameter should be set to default


Markus Rhein's picture

Unfortunately there also exist IGES files that only work with the paremeter set to the value -2 for instance and fail to load the IGES file correctly in all other cases... So far I don´t have a hint for the ´best´ default value.

axie.hi's picture
axie.hi's picture

hello davide,
it worked bad:There are redundant faces after IGES import. please give me a hand!

Forum supervisor's picture

Dear Davide,
I would like to inform you that the posted problem is checked and reproduced.
The corresponding issue with ID = 22715 has been registered.
Later you can know if the issue is resolved by checking references to the specified ID in OCCT Release Notes. The analysis of the issue will take some time depending on our technical capability and availability of resources.
If you can't wait and the problem is urgent for you, you may contact us via Contact Form http://www.opencascade.org/about/contacts/.
We will try to find a solution/workaround acceptable for you.