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.

Deleting Global Parameters in Revit

Following on from my earlier post about transferring global parameters between Revit projects, here is some information about what happens when you delete them.

Your list of Global Parameters in a project can get very long and messy - so eventually you'll need to do some tidying up.

Global Parameters Dialog Box

The Global Parameter dialog box has a 'Delete' function, not surprisingly - a red cross icon, next to the modify and create new icons.

A Global Parameter (GP) can be used in formulas for other parameters, and it can be associated to dimensions or elements in the project, so you need to be careful about deleting them - more so than in the family editor (where you have a better chance of knowing where they'd been used).

If a GP is deleted, then any formulas using that GP would also be cleared - it gives a warning, which is invaluable

If a GP is deleted, where it has been associated to elements, it also gives a warning with a number of elements to be affected - if you proceed all those associations would be lost. By comparison, in the family editor deleting a parameter would affect only that family, whereas with Global Parameters it could affect the whole project. So, be very careful

Elements in the Project

Elements in a project could have GPs associated with them, and deleting the element would obviously break/lose that association.  It is important to know when this is happening - or better still, beforehand.  When a dimension is deleted, it will warn you about constraints;  it does the same thing for GP associations to dimensions.

 

If you expand the warning it does not mention global parameters, but gives enough information to figure it out

Warning
If you delete an element that has a GP directly associated to one of its properties, it does not warn you - Revit just goes ahead and deletes it.  For this reason it is important to be able to check which elements have associations

Checking GP Associations

When you select an element that has GP controlled dimensions attached to it, all the related GPs show up on screen, including the label names. You can hover the cursor over any of the highlighted constraint dimensions for more detail in a popup tooltip.

 

It is a mystery why all those extra label names appear in this situation but not when you select an actual dimension. Sometimes it gets very messy and confusing

More on checking GP Associations by scheduling and view filters to follow . . . .