Reference Planes are Directional! Emily explains this property and how it effects extrusions.
A while back, when I first started teaching family creation I kept noticing that a few people in the class would end up with extrusions extending in the opposite direction than they intended. I chalked this up to inexperience and lack of practice with family creation. What I soon realized, was that it was I who still had something to learn!
Reference planes are directional! There is a front and a back to a reference plane and how you draw that plane, left to right or right to left, affects to which side the extrusion will extend.
With a little research and testing I learned a few things about reference planes that made everything involving their use less confusing.
The image below shows a standard generic model family template with the two original reference planes, Centre Left/Right and Centre Front/Back. I have drawn 4 extra reference planes and labelled them according to how I drew them. I then created an extrusion on each plane with a 1’-0” height and observed which direction they extended.
In the general project environment, extrusions function the same way.
In elevation, whether in a family or project, all extrusions placed on a plane will extend upwards unless a negative number is specified.
For every day family creation and extrusion of most elements in a model, whether the extrusion has a negative or positive height value doesn’t really matter. It won’t affect the function of the family. What is important is that we understand why we had to give it that negative value in the first place.
Another place where I found the drawing direction of the reference plane matters is when it comes to Model Text.
Here, I have made a Left to Right and Right to Left reference plane with matching Model Text. I then drew two walls, one from left to right and the other from right to left (just to see if it mattered).
I created some Model Text on the reference planes, both of which appeared correctly. I copied this original model text and used the Pick New to assign it to a new work plane. The text placed on the Left to Right reference plane appears inside the wall whereas the Right to Left text is placed correctly on the face of the wall.
I tested this with the other side of the same walls and again, the Right to Left text is properly placed on the face of the wall whereas the Left to Right is inside the wall.
No amount of negative depth can solve backwards lettering!
If your text will be remaining on a reference plane forever, the draw direction of the plan won’t matter. But if at any point you move it from that reference plane to an object face, you’ll see the effects of a backwards plane.
These parameter properties also apply to elements like lighting and other objects that might rely on a reference plane for placement. If you are linking an architectural model in to your MEP model and using a reference plane to host your lighting or plumbing fixtures, the direction of your reference plane will matter.
The way a family is created will change the way it sits on a reference plane. If you have ever looked at a lighting family, they are created upside down compared to an object like a sink and thus will sit differently on a reference plane.
The lighting family will sit on a reference plan in the opposite direction that a sink would, so when placing a reference plane for your lighting, you must know which direction to draw your plane to force your lights to sit properly.
Ultimately, each use for reference planes has some different rules to pay attention to. So long as you remember the rules for the style you create most often, your work should go smoothly.
Hope this cleared things up for some of you!
I hope this tutorial proves helpful to you as you use Revit to save you time and not duplicate processes. Check out my tutorial on How to Display Geodetic Information Alongside Your Project Elevation.
Pop your questions in the comments below and I’ll get back to you there, or give us a call.