Various transition ducts

[jfc4120]

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OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.2
Locale: English/United States (en_US)
Installed mods: 
  * Help 1.0.3

I have one program from Designcad 2000 (using basiccad) that handles numerous transition shapes.

You basically

[*]Draw the fitting
[*]Choose how many key points to click for each end
[*]Then the program triangulates and lays out fitting flat.

Note the pre clicking of points, it's the key to the program working.

Main question, is this possible in Freecad python, the usage of some stored clicked points (or line endings / midpoints) to use in equations?

Some images attached: Also the program works on all type of crazy transitions since it depends on the points to handle the analytic geometry and trig.

[edwilliams16]

Main question, is this possible in Freecad python, the usage of some stored clicked points (or line endings / midpoints) to use in equations?

They are all available via the Gui.Selection.getSelectionEx()
function. It returns a list of selected objects, and the locations clicked.

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sels = Gui.Selection.getSelectionEx()

Inspecting the first selection

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sels[0].SubObjects[0].ShapeType

would return 'vertex' or 'edge'
For a vertex

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sels[0].SubObjects[0].Point

would be its location.

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sels[0].PickedPoints

is the list of picked locations.

So there's not much to the required gui interface. It's easy to draw a line between two points, use Part.makeLine()
The challenge is all the book-keeping to create a valid triangulated shell to be unrolled.

FreeCAD's hierarchy here is
Vertex - Edge - Face - Shell

For a triangulated shell, you need a list of two vertices to make a (straight) edge. From three edges, you create a face. From a list of faces you make a shell.
Vertices are shared among edges, edges among faces etc. See https://wiki.freecadweb.org/Topological_data_scripting