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TransientBRep

September 3, 2026•

7 min read

Cap faces for a transient beam

A beam's start and end caps are planar faces shaped like the cross-section. The boundary is a closed list of profile curves — lines, arcs, full circles, ellipses — each becoming one edge in an edge loop. Hollow sections add inner loops on the same face, walked the other way round. This post defines the profile representation used by the rest of the series, extends the bridge with arcs, circles and ellipses, and builds the cap face for a rounded RHS with a rectangular inner contour. Part of the transient-beam series.

Getting a transient body on screen in Inventor

A transient SurfaceBody is invisible until it is added to client graphics. This post sets up the object every later sample draws through — a base class that owns a ClientGraphics and GraphicsDataSets pair under a client id, hands out uniquely numbered GraphicsNodes and cleans up in one call — and a console application that attaches to the running Inventor from outside its process and draws into the active document. With what Inventor does about the undo list, the dirty flag and ActiveView. Part of the transient-beam series.

The TransientBRep construction tree in Inventor

TransientBRep.CreateSurfaceBodyDefinition() returns the root of a tree that describes the topology of a SurfaceBody — vertices, edges, edge loops, faces, shells, lumps. Once the tree is populated, one call to CreateTransientSurfaceBody produces the body. This post walks the tree, sets up the small managed-geometry bridge the rest of the series uses, builds the smallest valid body — a rectangular planar sheet — and records what Inventor does with the errors map, loop winding and mismatched curves. Part of the transient-beam series.

Constructing a transient beam in Inventor

Inventor's TransientBRep API can produce a SurfaceBody that lives outside the document — no undo, no sketch, no extrude. The pieces are well-named (SurfaceBodyDefinition, LumpDefinition, FaceShellDefinition, FaceDefinition, EdgeLoopDefinition, EdgeDefinition, VertexDefinition) and the surfaces and curves come from TransientGeometry, but there's almost nothing public about how to glue them together for anything beyond the built-in primitives. This series walks the full construction path, end to end, using a beam as the running example, with every sample compiled and run. First post in a series.

Inside Frame Generator, Part 3: Surviving Replacement

When a Frame Generator user changes a beam from HEA200 to HEA240, every reference key, assembly constraint and proxy that pointed at the old beam is invalidated. Here's how to survive: tag every dependent with a GUID-keyed attribute, then on the next edit search by attribute and recreate the broken pieces against the new component definition's work-planes.

Inside Frame Generator, Part 2: Tracking Edits

Frame Generator has no 'frame edited' event. You stitch one together from OnActivateCommand, OnTerminateCommand, OnDelete, OnNewOccurrence, OnOccurrenceChange and OnCommit — plus two magic command names and the literal string 'Change Frame' as a transaction-name match. Here's the actual sequence and the kBefore/kAfter ordering you have to respect.

Inside Frame Generator, Part 1: The Data Model

How Autodesk Inventor's Frame Generator stores frame members: the com.autodesk.FG attribute set, the Frame.Skeletons XML payload, three different IDs and which one survives a profile change, and why attribute lookups need GetNativeOccurrence() rather than the proxy you receive from events.

Inventor 2027 Entitlement & .NET 10 Migration for Paid App Store Add-ins

Autodesk's compatibility note for Inventor 2027 says existing .NET 8 add-ins should keep working without recompilation, and for most add-ins that's accurate. The exception is paid App Store add-ins that call AdWebServicesWrapper to verify entitlement — free add-ins typically skip that check, so they're unaffected. The wrapper was renamed and retargeted to .NET 10 in 2027, so paid App Store add-ins do need a migration. Here's the conditional TFM / per-version reference / manifest-gate pattern I rolled out across 7 add-ins.

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