Parametric windows in arch workbench VS external geometry

[invader]

I'm new in FreeCAD and I'm not sure if its a bug or my bad understanding. I want to make Parametric Windows in Arch Workbench.

OS: Ubuntu 18.04.1 LTS
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.15650 (Git) AppImage
Build type: Release
Branch: master
Hash: c9b4f4ba6779c9ccddb69fba57eee1b5acfd4083
Python version: 2.7.6
Qt version: 4.8.6
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

First note that the Window-Sketch007 is linked to external geometry.

1.png (173.87 KiB) Viewed 238 times

Now I want to make a new window based on the Sketch010.

2.png (213.74 KiB) Viewed 238 times

The new Window-Sketch010 appeared, but note all the windows are messed up.

3.png (206.47 KiB) Viewed 238 times

Now note that the Window-Sketch007 is linked to *different* external geometry. The same happened to all other windows sketches.

4.png (172.99 KiB) Viewed 238 times

[Roy_043]

Basically the problem is our arch-enemy number one bug in freecad: TopoNaming.
Each edge in an object has a number: Edge1, Edge2,... When an object is recalculated, that numbering order can change. And any other object that is using an edge from the first one, might suddenly pick another edge because its ordering has changed.
This is a problem in OpenCasCade, the geometry engine of FreeCAD, and therefore it's very hard for us to find a solution. Many have been and are still actively trying. No doubt some day we'll have a solution, but it might take time.

Sketches are particularly vulnerable to that problem, because the solver can take an infinite number of possible paths to solve a sketch. The more geometry and constraints there are in a sketch, the more "hasardous" it becomes. Draft objects, on the other hand, construct their geometry always in the same order, so they are much more predictable and stable.

But when you grow used to sketches, you learn to cope with their volatility, and most long-term freecad users know well how to avoid most of the problems. Basically try to keep them simple and not make very complex sketch-depending-on-another-sketch situations

[invader]

OK, now I get it. So my work around is:
- Create fully constrained sketch with external geometry reference, then delete the external geometry reference.
- Make a window based on the sketch.
- When all the windows are done, redo all the external geometry references if you need them.