Why does autocad drawings require so much mesh fixing ?

Recently i had to do some 3D animations / renders on autocad drawings.
Since i didnt have good converter tools, i just asked them to deliver it in obj, or 3ds format.
I dont know exactly how they all did it, from one customer i know he used sketchup pro to convert it.

Anyway what i notice from all those drawing, that every time, they have problems.
Like 3D objects who are not truly 3D, ea missing faces.
Or like with engraved features have separations at unlikely places.
Poorly meshed rounded corners etc, strange triangulations on cylinders with holes etc.
unconnectedvertexes etc, doubles, …

I don’t know how conversion works, but I’m guessing the tools they used don’t invent mesh layouts.
And i wonder how can it be that such files can be used in CAD/CAM applications if they contain that many errors.
Surely autocad should be able to generate drawings with good mesh layouts

So are such errors a result of poor conversions or poor autocad drawing skills, … or ?.

The point is when i give them a time estimation for such a job i can’t really anticipate on the time that i require to fix their drawings, and in some drawings i lost a lot of time with it.

Perhaps there are some tips i should give those people, so that they can send me better meshes ?

CAD programs usually work with parametric NURBS surfaces, not polygons. You can think of it as vector graphics in 3D with smooth lines etc. Poly mesh is able to approximate smooth curves with lots of small flat faces but it is still an approximation, not exact representation.

Conversion from NURBS to polygon mesh is not a straightforward thing, so errors easily creep in.

did u use the proper import script ?

there is also an SVN for CAD things
the 2.49 is free
but the 2.5 has a fee!

happy bl

I work in both blender and autocad. The problem is that the data is stored in a different type of format. Nurbs or Solid models have completely different ways that the software defines the geometry than polygonal modelers like Blender. The conversion tools all lose some degree of fidelity.

The best workflow I have discovered with this pipeline is to export the model as a series of .stl files. I still have to clean up the topology, but the geometry itself comes in fairly clean.

I know what a pain cleaning up imported models can be. Anytime I am receiving cad files, I make sure to include time in my quote for processing cad files.

Export from Autocad as DXF

and import in Blender as DXF.

I do this with Rhino a lot and thus get all my 2D NURBS curves into Blender nearly 1:1.

You mean that Rhino is the perfect conversion tool for Autocad ?

I can’t speak for cekuhnen, but no, it isn’t the perfect conversion tool. He was talking about a good pipeline for accurate 2d curves and lines. autocad -> rhino -> blender isn’t going to magically fix the problems with importing CAD files, you’re still going to run into the same issues.

Oh while I teach Autocad in interior design I hate that software.
For design work I mainly use Rhino or Alias.

So from Autocad as stated save curve designs as DXF and 3D models export as OBJ.

Sadly Blender has no NURBS importer - somebody worked on a rhino importer and then dropped it …