Export step problem

[happydpc]

Export step fail

After ruling the surface, the export step file failed at Serialize the Edge with cur3d is "Path". Because path not impl IExportStep interface.

Here's the testcase file.
test_ruled.cdb.json.zip

[dsn27]

This error happens because CADability.GeoObject.Path does not implement IExportStep.
Thus the cast (curve3d as IExportStep) will return null.

Either implement the interface or use a safe cast.

https://github.com/SOFAgh/CADability/blob/24181919cb5678058b73b3900441a07a826c7ac9/CADability/Edge.cs#L3567-L3575

System.NullReferenceException
HResult=0x80004003
Message= Object reference not set to an instance of an object
Source=CADability
StackTrace:
at CADability.Edge.CADability.IExportStep.Export(ExportStep export, Boolean topLevel) in C:\Development\Repos\SOFAgh\CADability\CADability\Edge.cs:line 3572

[x68507]

It looks like my file containing only a circular surface might have the same issue.

CADability can import correctly but it cannot export the surface as a STEP file. The export fails and programs like NIST STEP File Analyzer and Viewer cannot even parse the exported STEP file. It looks like the EDGE_LOOP has no reference entity and the B_SPLINE_CURVE_WITH_KNOTS & corresponding CARTESIAN_POINT are never written to the file.

fma_02-good.zip