Hello,
I am not that familiar with the way Collada works (whether it has real world units, or just drawing units like AutoCAD), but I think you can rule out if it goes bad during import or export, if you open the DAE file in some kind of 3rd party Collada viewer application.
But better yet, if you select 'File>Save As...' with the 3D window open and front, you can save directly in 3DS format and avoid all this hustle. If you need to import a 3DS file back to ARCHICAD,
you can use the 3D Studio-In Add-in (part of the Goodies Pack) to do it.
Regards,
Daniel Alexander Kovacs
Professional Services Consultant
GRAPHISOFT
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