Techdraw Dimensions

[garybarnes59]

As a new user to Techdraw I have to say the issue of dimensions collapsing when the model is change is a monstrous elephant in the room.

I have read about the Topological Naming Problem, which explains why modified parts may lose a dimension or two, and would be acceptable. However it doesn't entirely explain why dimensions dissolve into garbage when a new object is added to the Techdraw view. Is it because, say, when an edge is lost, TechDraw grabs the nearest candidate causing the whole thing to collapse like a pack of cards? Anyone with real life experience of engineering (and not just 3D printing) will understand that refinement and change is an integral part of the design process.

Having used AutoCAD for years I enjoyed learning the different approach offered by FreeCAD and I think FreeCAD is excellent. It's a shame that a fundamental engineering requirement has been allowed, apparently, to fester unresolved for years.

I would say that resolution of this issue is vital to the project.

[chrisb]

I would say that resolution of this issue is vital to the project.

You are right here. The problem is, that there is nobody to blame, and you can point to nobody who should do it. However, you can support the ongoing work by reviewing pull requests to the Toponaming branch and by testing it.

[garybarnes59]

I'm finding that things are much more stable when dimensioning vanilla top-level parts (bodies).

What exacerbates the problem is when part of an array, linked set, or nested linked objects are include in the view selection.
When selecting part of a linked set I notice the parent is also automatically included in the selection.

It's not unreasonable to expect dimensions to become unlinked when a part is modified or deleted (limited to dimensions associated with that part). What is not reasonable is for dimensioning across the piece to fail when saving and re-opening a file, or when parts are moved, or a new part included in the view.

Look, I'm sorry if this seems like harsh criticism of what after all is a fantastic (and free) piece of software. As a new user it just looks like it has been an ongoing issue for years.

[ChemicalCoal]

Look, I'm sorry if this seems like harsh criticism of what after all is a fantastic (and free) piece of software. As a new user it just looks like it has been an ongoing issue for years.

Totally correct, criticism is what drive improvement.

The cause is pronounced in this example, where 2 parts are positioned, and upon moving the forward object behind, the dimension gets messed up. No geometry changes and the points that were originally dimensioned are completely unchanged. It appears the error occurs because the dimensions are not attached to the 3D model, and instead the 2D model. The TNP rears its head, and upon any updates to the view there is a chance the vertex names shift to other points, and all the dimensions change to these new points.



@garybarnes59 I have found the "3D" dimensions, which reference points on the model are substantially more robust than the default "2D" dimension that references the drawing, and in general they are only marginally more difficult to setup. They still have the standard 3D model TNP issues, but completely avoid any TNP issues from the 3D to 2D conversion.

Checkout this pull request: https://github.com/FreeCAD/FreeCAD/pull/8141

I agree, this is annoying, where any small changes to a part risk needing to completely remake the drawing.

I think the ultimate solution is once the TNP is fixed, every dimension by default should be "3D" or rely on the model instead of flattened version.