Exported solids using EZDXF are not behaving as expected in AutoCAD using Dynamo for intersection of solids

[kvermeulen26]

I am working on a project where we generate 3D solids based on polygons with a height and material, export these to DXF so a CAD modeller can make extrusions with Dynamo and calculate volumes using these intersected solids.
While the export in solids seems to be working (massprop command in AutoCAD works on exported solids), the intersection script in Dynamo does not work properly on the exported solids, while it works properly on solids created within AutoCAD itself.
This suggests the solids created using ezdxf are missing some metadata or the data structure is somehow different. I ran the info and audit commands on the DXF export:

Filename: Path/ DXF_export_model.dxf"
Format: ASCII
Release: R2018
DXF Version: AC1032
Codepage: ANSI_1252
Encoding: utf-8
Layouts:
'Model'
'Layout1'
Created by ezdxf: 1.4.0 @ 2025-03-24T13:53:49.162567+00:00
auditing file: path\DXF_export_model.dxf
No errors found.
This is my code creating the 3D solids using ezdxf. I do not have much experience with ezdxf so I hope somebody can perhaps point out some possible errors in how these solids are created:
def save_to_dxf_3dsolid(polygon, base_height, top_height, msp, material, surface, color):
if round(base_height, 2) == round(top_height, 2):
return 0

try:
    # Create a mesh that represents the extruded polygon
    mesh = ezdxf.render.MeshBuilder()

    # Get the polygon points
    points = list(polygon.exterior.coords)
    if points[0] == points[-1]:  # Remove duplicate last point if it exists
        points = points[:-1]

    # Create bottom face
    bottom_points = [(x, y, base_height) for x, y in points]

    # Create top face
    if surface is not False:
        top_points = [(x, y, nearest_points(surface, Point(x, y))[0].z) for x, y in points]
    else:
        top_points = [(x, y, top_height) for x, y in points]

    # Add bottom face to mesh (reversed for correct normal direction)
    mesh.add_face(list(reversed(bottom_points)))

    # Add top face to mesh
    mesh.add_face(top_points)

    # Add side faces
    for i in range(len(points)):
        next_i = (i + 1) % len(points)

        # Define the four corner points of this side face
        quad = [
            bottom_points[i],
            bottom_points[next_i],
            top_points[next_i],
            top_points[i]
        ]

        # Add the side face
        mesh.add_face(quad)

    # Try to create an ACIS body from the mesh
    body = acis.body_from_mesh(mesh)

    # Create a 3DSOLID entity
    solid3d = msp.add_3dsolid(dxfattribs={'layer': material, 'color': color})

    # Export the ACIS body to the 3DSOLID
    acis.export_dxf(solid3d, [body])

    # Try to force AutoCAD to recognize this as a true volume-bearing solid
    # Add extended entity data to indicate this is a volume solid
    solid3d.set_xdata('ACAD', [
        (1000, 'ACIS_SOLID'),  # String marker
        (1071, 1)  # Integer flag to indicate true solid
    ])

    return solid3d

except Exception as e:
    print(f"Error creating 3DSOLID: {str(e)}")
    return 0

[mozman]

The ACIS support of ezdxf is very basic, don't expect full feature support. You are lucky if get your 3D data into AutoCAD and that's it and there is no advantage over using MESH entities directly.

If you need better 3D support you have to use an OpenCascade base library or application like

• build123d
• FreeCAD (scriptable in Python)

But now you have different problem, none of the free and open source libraries and applications support ACIS import/export. So you have to use simple mesh based formats like STL or 3MF for import/export. Or you find a way to process BREP or STEP files. None of the solutions is ideal.