Please Note: Our Discussion forums have moved. If you would like to discuss this article or any aspect of Revit, please do so at www.forums.revit.biz We will be more than pleased to help you with ANY Revit query. Welcome to Part 10 of this 17 part series on creating your own custom 3D components within Revit. If you haven’t read any of the other articles, I strongly suggest you check out Part 1 which acts as an index to the series. In this particular article we are going to take a look at Reference Planes and Reference Lines. We will look at what they are, the key difference between them (Planes and Lines) and examples of how, when and why you would use them. In order to talk about Reference Lines and Planes, I’m going to start by mentioning Levels. Hopefully you are familiar with the concept of Levels within Revit? As you know Levels are very useful. They give you a degree of control over your elements. For example if you have two Levels- which between them constrain the base and top of a wall element; then just by changing the height of the Levels, you immediately control the extents of the Wall. Reference Planes and Lines are a little like this. They allow you to form datums, which other elements can relate to. Any changes to the datums result in a corresponding change to the element. The key word in the last sentence is “CHANGES”. Reference Lines and Planes are most useful when you are creating components that need to CHANGE- ie they are controlled by Parameters. Reference Planes Let’s start by taking a look at Reference Planes. These are typically used for creating a “skeleton” to which sketch lines or mass elements can be locked to. Why would we want to create a skeleton first? Can we not just sketch out (say) a profile we want to extrude? Yes, we can- but we have nowhere near as much control over that object than if first create a parametric skeleton from Reference Planes. Let’s take a look at a quick example to help explain the concepts….. Let’s use the Generic Model template to create a very basic extrusion…. 
In the image above you will see that I have just arbitrarily sketched out the base for my extrusion. If I go ahead and give it a height, complete the Sketch; I get….. 
A very basic cubic mass element. But let’s go back to the beginning and create something that’s infinitely more useful. This time before I create the Extrusion, I’m going to form (from Reference Planes) a “template” for it’s base. Using the Reference Plane tool…. 
I draw 4 Reference Planes. I name each one of these by selecting them, selecting their Properties Control Panel and typing in a unique name for each one…. 
I’ve named my 4 like so “Top”, “Bottom”, “Left” and “Right”. It is crucial that you get into the habit of naming each Reference Plane that you create. Now I have a basic skeleton for the base of my Extrusion, I’m going to add some Parameters to it BEFORE I create the Extrusion itself. It is important to note the order- I’ll say it again for clarity: Form the skeleton from Reference Planes, Add you dimension parameters to this skeleton- so that changes to the parameters cause the skeleton (ie the Reference Planes) to move and THEN add your sketch lines (for the base of the Extrusion) to the skeleton. Failure to work methodically in the correct sequence will result in unpredictable results that are VERY difficult to unravel later! 
So here is my parametric skeleton formed from Reference Planes. It is ALWAYS a good idea to test (or “Flex”) your creation at this point. Just bring up the Family Types Control Panel…. 
And type some different values into your “Length” and “Width” parameters. Hit “Apply” and see if your Reference Planes move accordingly (they should be constrained by the Parametric Dimensions)…. 
Notice how the Reference Planes do NOT remain equidistant from the Origin Planes. If we require them to do so (which often we do) we would need to add further constraining dimensions (and set them to “Equal”). If we are happy with how the Reference Planes work (with respect to varying parameter values), we can go ahead and add our solid mass to this skeleton. Let’s sketch out a base for an Extrusion…. 
Here is the base of my Extrusion, sketched out using “Sketch Lines”. NOW for the IMPORTANT step. Select each sketch line in turn and make sure it is locked to it’s corresponding Reference Plane by clicking on it’s padlock….. 
NOTE: If you can’t see the padlock symbol, don’t panic! Just do the following: Pick each line, drag it AWAY from it’s Reference Plane and then drag it BACK onto it’s Reference Plane- it will snap back in place AND the Padlock symbol will appear for you to click!
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