I've been inspired to have another go at using Mstn Constraints and Parametric modeling.

As mentioned elsewhere, Revit can be a bit too reliant on Work and Reference planes when it comes to modeling. Setting up all those 'constraints' geometry then binding the primary geometry to the reference planes can be a bit much. Using a Revit toilet cubicle example, I thought that I would try to replicate the design in OBD U9.2 (Mstn 16.3).

I have to say, I ran into all kinds of problems trying to use 3d Constraints to position elements parametrically with respect to each other. So, I went back to setting up some 2d construction geometry that I would constrain first. This is similar to the old DDD workflow.

1. Place two Lines so that they intersect each other, the use the 2d Coincident Constraint to constrain a 3d solid to both Lines. The result is not very useful. Moving the any of the Lines is blocked. And you will can not move the Cylinder to follow the lines. Moving the Cylinder does move the constrained lines. So, not the bi-directional constraints solving behaviour you would expect. Doesn't matter if you pick the Lines or the Cylinder first. BTW: the Cylinder is intended to replicate the cubicle partition supports in the Revit vid above.

2. Redo the steps but instead constrain a 2d Circle to the lines. Flexing either the Circle or the Lines work as expect. The geometry moves around to preserve the coincident relationships. Bravo!

Now, you can constrain concentric the 3d Cylinder to the 2d Circle which is constrained to Lines. And move any of the four elements around and the Constraints work as expected.

Why?

It would be good if Bentley could publish some info on how the constraints work with each other and when both 2d and 3d elements are involved. Most users would not expect to have to use a 2d 'go between' to control a 3d element. Is there a priority list involved? Is the solver looking to solve 2d to 2d constraints first? And if it finds a 3d element in the solving set it moves to a 3d first or only behaviour?

It would be good to know. At the moment Revit is winning when it comes to ease of use.