Issues with SurfaceBody.CalculateFacets in Inventor 2025 Add-in (.NET 8 / x64)

[ewoudQDYF4]

Hi everyone,

I’m working on an Inventor 2025 add-in in C# (targeting .NET 8, x64) that fingerprints parts by falling back to a mesh-based hash via the SurfaceBody.CalculateFacets API. Although I can successfully compile against Autodesk.Inventor.Interop.dll, at runtime every call to CalculateFacets fails with a type-mismatch error and returns zero vertices:

less

FOUT in CalculateFacets voor body: Type mismatch. (0x80020005 (DISP_E_TYPEMISMATCH)) [MeshHash] Totaal vertices gevonden: 0 [MeshHash] Geen vertices gevonden, hash blijft leeg.

My environment:

• Inventor: 2025 (fully updated)

• Visual Studio: 17.8+, targeting .NET 8 SDK

• Platform: x64 build

• Interop settings:

  • Embed Interop Types = False

  • Copy Local = True

What I’ve tried so far:

1. Confirmed the add-in DLL is loaded in the x64 Inventor process.

2. Referencing the Inventor 2025 interop DLL from C:\Program Files\Autodesk\Inventor 2025\Bin.

3. Various overloads, including:

   csharp

   body.CalculateFacets( 0.01, out int vertexCount, out int facetCount, out double[] vertexCoords, out double[] normalVectors, out int[] vertexIndices );

4. Using out object parameters then casting.

5. Verifying that each SurfaceBody actually has faces.

Questions:

• Is there a different COM signature or overload for CalculateFacets in Inventor 2025/.NET 8?

• Do I need to pre-allocate arrays or use a special marshalling attribute?

• Has anyone successfully used CalculateFacets under .NET 8/x64 with Inventor 2025? A minimal working example would be hugely appreciated.

Attachment:
I’ve included the full SmartCopyExporter.cs source as a TXT attachment for reference.

Thanks in advance for any pointers!

[julian_sol]

I have encountered the same issue too. It appears to be a bug in the Inventor API.

In the VBA Editor within Inventor itself this method does work:

Dim vertexCount As Long
Dim facetCount As Long
Dim vertexCoords() As Double
Dim normalVectors() As Double
Dim vertexIndices() As Long

Call oBody.CalculateFacets(tolerance, vertexCount, facetCount, vertexCoords, normalVectors, vertexIndices)

But in C# it gives the error: Type mismatch. (0x80020005 (DISP_E_TYPEMISMATCH)) 

int vertexCount = 0;
int facetCount = 0;
double[] vertexCoords = null;
double[] normalVectors = null;
int[] vertexIndices = null;

body.CalculateFacets(tolerance, out vertexCount, out facetCount, out vertexCoords, out normalVectors, out vertexIndices);

Maybe it's because in VBA it requests a Long and in C# an int?