Saturday, 29 April 2017

Weird Stuff with Global Parameters in Revit

Following on from my earlier posts about transferring global parameters between Revit projects, and deleting global parameters, here is some quirky stuff that happens when you are working with Global parameters:

Weird Behaviour & Bugs

1.   Duplicate Labelled Dimensions

If you add a dimension to elements that already have a ‘global parameterised’ dimension, the new dimension automatically takes on the same parameter, without you realising.   If you subsequently delete that dimension, you get a message saying ‘A Dimension that is labeled . . .’  Unconstrain to remove constraint

  • If you expand the warning, it tells you what the Parameter label is
  •  It does not tell you that you are deleting a secondary (redundant) dimension with the same label as another dimension, which still remains in the model

 2.  GP Equals Constraint Conflict – Fixed in v2018 (?)

If a dimension between two elements (say gridlines) has a GP associated to it, then you place a dimension between the grids and an element midway between them, you would expect to be able to change that dimension to ‘Equals’. Illogically, Revit does not allow this – it warns you that it needs to remove the constraint. Unfortunately if you go ahead, it removes the GP constraint but keeps the Equals constraint – which is not very helpful as you now need to guess which other constraint it removed. It does not highlight the other constraint

  • I recommend that you cancel, then figure out where the conflict is - do not click on 'Remove Label'
  • One solution to this is to create another GP that is a fraction of the original one (half, in this example), and apply that to the secondary dimension, instead of an equals constraint

  • Another solution is to put the equality constraints between other elements that are in the same location but not GP dimensioned – eg between two walls that are aligned to the gridlines.
  • NB. This problem does not occur if the GP associated dimension is a reporting parameter.
  • This bug is reportedly fixed in v2018, but I have not had time to test it yet

3.  Edit Witness Line Bug

If you associate a GP to a dimension, and then subsequently delete the dimension, Revit will ask you if you want to unconstrain (remove the constraint) – this is good behaviour. However, if you edit a witness line instead of deleting the dimension, Revit removes the GP association (as you would expect), but does not ask if you want to remove the constraint – effectively hiding the constraint. This is really bad behaviour by Revit, because it means you can end up with lots of hidden constraints, which catch you out later on. Autodesk refuse to accept that this is an inconsistency in the software that should be changed. I recommend that you never edit a witness line on a GP associated dimension.

4.  Shape-Handles vs Calculation

If you have a family that has grip handles when placed in the model, those handles can be ‘hidden’ when GPs are associated with certain properties in the family. This happens if the property is used in a formula that drives the geometry related to the shape-handle:
  • No GPs associated – shape-handles available
  • GP associated to a property used in width formula

  • In this situation, it is better not to associate the GP directly to the property. Instead you need to use a dimension with a reporting GP associated to it. Then the association is far enough removed so the shape-handles are unaffected.

5.  Circular Chain of References

  • At some point you are likely to encounter this warning dialog:

  • I strongly recommend that you do not click on ‘Resolve’ because it will remove a formula, but not necessarily the one you are expecting, nor the one you just added that caused the problem. Instead you should cancel and figure out what is causing the problem – first click on ‘Expand’ to see if you can figure out the conflict; although using the ‘Delete Checked’ option does not seem to resolve anything (the same dialog just as likely pops up again), so you will then have to cancel anyway.

6.  Change Instance to Type

If parameters are changed from instance to type in a family, then reloaded into a project, you may get this message if the parameters had been associated to GPs

  • You then have to reassociate the property to the GP – but it is easier to do as it is likely to be only one type property to relink

7. Duplicate Type Loses Associations

If you duplicate a family type that has GP associations to any type properties they lose the associations.

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