Scan Rig
Scan Rig gives a scanned section a skeleton. You place points down the centre of the tube in the viewport, and the node joins them into a skeleton that Scan to Tube uses to rebuild the section as a clean tube. It's the second step of making a tiling bark texture from a scan, after Scan to Parts. It's on the Natsura toolbar under Scans.
Inputs and outputs
Wire the section from Scan to Parts (its first output) into the first input, Mesh. The second input, Profiles, isn't used. The output, Skeleton, goes into Scan to Tube's second input.
Placing points
With the node selected, press Enter in the viewport. In the default Trace mode, click to drop a point at the centre of the tube under the cursor, drag a point to move it, and middle-click a point to delete it. The right-click menu has Toggle Gizmo Edit Mode, for moving a selected point freely with a handle, plus Reparent to Selection…, Remove Selected Point and Clear All Points.
Each point is an entry under Number of Points, with its Location, Radius and Parent Point.
Status
Scan Rig is experimental and is only useful for making tube sections for now.