REVIT and math/logic

[pablo_etsl]

I´m wondering whether there is something fundamentally flawed in the software or whether I am confused about how it works.

One thing I noticed is that sometimes REVIT doesn´t like small dimensions. It gives errors when creating thin features in families, or defining distances between curtain walls by less than 40mm. Coming from a background in Mechanical design CAD, I find these errors unnecessary and un-forgivable.

The other area where I often run into difficulties is constraints, in the family editor. It is as if REVIT has an internal hierarchy of what it constrains things to, that will take precedence over constraints placed by the user.

Consider for example the following family:



The rectangle is fully defined and constrained to the reference planes. If we try to modify the angle, then it gives the following error:




In the generic family template, this can be solved by labeling the angular parameter, in this particular case. But it is just an example where the constraints that revit uses to calculate the position of geometry are definitely not those that the user has defined and sees.

Does anyone have any insights into how the program works, and how to circumnavigate these issues?

[Dimitri Harvalias]

Welcome to the forums Pablo.
When dealing with angular geometry you will have bette results if you use reference LINES not reference PLANES in the family editor. In the example you've shown the figure is not as fully defined as you might think. If you change that 30 degree angle where is Revit to consider the 'pivot point' for the geometry so the rectangle stays constrained?
Once you get used to the way Revit operates it will become easier.
As for the small dimension issue, what do you consider 'small'? What kind of parts are you modeling?

[pablo_etsl]

Thank you for the answer Dimitri.

I´m aware it isn´t fully defined, and I would think this is all the more reason to keep the constraints that have been placed - i.e. there is "more than one solution" instead of "no solution" which is what the error message seems to indicate. In any case, there are family templates where the option for a ref line seems not to be there (example is a mullion profile). On the other hand, the fact that points are not available in the family editor as references makes it difficult to define pivot points: work arounds involving placing more references combined with sketch geometry often give me errors similar to the above.

Maybe you could point me in the direction of some "best practices" when constraining sketches, or what the hierarchy is that Revit uses when deciding what dimensions to break and which to keep. In the above example, I have the suspicion it is really using the orthogonal "coordinates" of the dimensions placed in the rectangle, and not the dimensions itself. Could this be the case?

Thanks!

[Dimitri Harvalias]

There is no point object on its own butpPoints are available as part of the reference line objects if you tab select them. there is a hierarchy and Revit will establish 'automatic' sketch dimensions that may help you understand how things are governed.
See the attached example that uses ref lines and, as a result, does not require the angular constraints to keep the interior angles at 90 degrees.

Constrained Rectangle.rfa

Edit: Steve Stafford has a few posts covering the topic of automatic sketch dimensions on his blog revitoped
http://revitoped.blogspot.ca/search?...tch+dimensions