@Anonymous
You need to have a start point for the Route. You cannot select geometry but you can select any origin or work point in the main assembly. You now need to include this geometry as follows.
Method1: Include Origin Geometry in the Tube and Pipe Route (T&P) route
Start a route and in the ribbon tab select include geometry, now select any origin or work point either in the Main Assembly or T&P Assembly. The geometry should now be referenced in the T&P route folder.
Method2: Create work point Include Origin Geometry in the Tube and Pipe Route (T&P) route
Create a work Axis and Work point at the Top Assembly Level or where ever you need it. Return to T&P Run and repeat
Method3: Insert a fitting and Connect to Top level Assembly Geometry
Insert a fitting and connect to Top level Assembly Geometry, then connect route to this fitting.
Method4: Insert a Pretend fitting and Connect to Top level Assembly Geometry
Insert a Pretend fitting( a pipe with 1mm or less size and connect to Top level Assembly Geometry, then connect route to this fitting.
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Regards
Alan