WISH: join when importing IGES

When importing IGES file (containing polysurface(s)):

  • CATIAv6 joins the polysurfaces and the result is a single object (joint)
  • Rhino6, despite the iges being exported from Rhino, it doesn’t join the surfaces even though they have the same name.

I wish that either the surfaces with the same name inside the iges are joint upon import in Rhino. Or at least to have an option upon import asking if you want to join them.

I know I can do this with python, but I feel it will be much more performant if it is done with Cpp (I assume all file export/import operations in Rhino are still done with Cpp)

Thanks in advance.

This is intentional behavior since Rhino V1.

The idea is a damaged IGES file can be imported, inspected, and fixed.
Pursuant to this, one of the things Rhino has always done is to not Join the surfaces.
Rhino ignores meshes that can be in IGES files too.

STEP tries to Join the surfaces when imported.

Is this open for discussions? At least to have it optional or as a separate import command?

e.g. to have an optional boolean argument when launching the command: _import -join

Everything is open for discussion, but I have no idea how much traction it might get.

What would be the benefit of using step instead of iges? I know step is some sort of evolution to iges that didn’t really succeed in replacing it :slight_smile:

Besides the fact that the surfaces will be joined.

I’ve added it as a Wish item:

When Rhino reads a STEP file, the surfaces that make up a designated closed solid are Joined. They are not Joined when using IGES.

If you need a Solid and don’t want to Join them yourself, the STEP advantage is Rhino tries to Join them for you.

Thanks for that.

About the STEP’s advantages, I wondered if there is something else as an advantage. Like reduced file size or transferring attributes, because in IGES you can only transfer colors and names, perhaps layer (but I’m not sure)

They are just different. Since I’ve never needed to use either format professionally, I’m not a good resource.

The complaint about IGES is surfaces that make solids are not Joined.
The complaint about STEP is they use Rhino “Blocks” instead of Layers.

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The reason for this is that IGES files do not contain any “join” information - it’s not part of the file format specification. That is one of the advantages of STEP, information on things that are “joined” is exported with the STEP file and can be read on import.

So other applications manage to do this by magic and trickery?


IGES models are surface files and as such have no mass properties information; though there is an IGES standard for solids (IGES-MSBO), it is rarely used.

If some programs think what is being imported is only one single volume, it then it will try to join them - Rhino makes no such assumption.

You know what, I retract my previous statement.

I did some tests. I am wrong CATIA does not join them.

I don’t know why I thought it did.