Family Creation: Locking Center Points to Reference Lines

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Family Creation: Locking Center Points to Reference Lines

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Note: Everything discussed below is in reference to family creation, but could also apply to working in a project file. This post assumes some level of pre-existing Revit knowledge – post a comment UPDATE: we’ve disabled comments due to spam… send me an email at if you’d like to have anything in this post explained in greater detail.

I was reviewing a family recently where we had a solid cylinder, created from an extruded circle, sitting on top of another surface. The extrusion’s radius and height were locked and/or parameterized, but in a 3D view, you could select the extrusion’s radius grips and move the cylinder around – it was not locked into place. Additionally, we wanted to locate the center of the cylinder relative to the family’s origin by measuring its angle from vertical and distance from origin.

Now, I know there’s a way using trigonometry to do all sorts of fancy things here, but there are days when I really don’t want to remember that part of my life and education, and this was one of those days. Instead, I wanted to create a reference line, apply ‘distance’ and ‘angle’ parameters to it, and then have my cylinder follow it around.
Have you tried locking the center of a circle to the endpoint of a reference line? No? Here’s the fun part… if you dimension the distance from the end of the reference line to the center of the circle used in the extrusion, or use the align command to align the center of the circle to the end of the reference line, it will only align or lock in one dimension – horizontally or vertically… not both. Depending on how you do it, it might not work at all.
Let me introduce you to “Automatic Sketch Dimensions”! These are dimensions that Revit automatically places (and hides from us) to control how different objects move relative to each other. To see these dimensions, go into your view’s Visibility / Graphics controls, Annotation Categories tab and fill in their check box. You will want to leave the visibility of these dimensions off whenever you are not actively using them – they can make your screen somewhat cluttered and confusing otherwise.

By default in the family I was reviewing, the automatic sketch dimensions were positioning the circle in my cylinder extrusion relative to the origin reference planes, not the end of my reference line. To see this, I had to edit the extrusion – those automatic sketch dimensions are “inside” the extrusion and unless you are also “inside” the extrusion, you won’t see them even if they are turned on in Visibility/Graphics.

Once these dimensions are visible, you can select them and move the witness lines to dimension from the center of the circle to the end of the reference line. Once they are correctly positioned, select the circle, and the automatic sketch dimensions become editable. Change their values to zero and lock them down. Finish editing the extrusion, turn off the automatic sketch dimensions, and you now have a cylinder that follows the end of a reference line!


About the author

Based out of Denver, Colorado, Joe is a Professional Services Manager for Avatech Solutions, managing a dedicated team of services professionals to ensure that the people, technology and processes exist to provide the best possible solution - every time. As experts in leading building design and engineering firms through the process of selecting, implementing, and optimizing software solutions, Joe develops new workflow processes that dramatically improve productivity and efficiency. Specializing in the customization, optimization, and integration of Autodesk building design and engineering products, Joe helps AEC firms navigate the road to building information modeling (BIM) using a logical progression from 2D to full BIM. His years of experience in the industry make him an able leader in the management of cultural changes necessary for firms to be successful. You can find Joe on LinkedIn.

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