Modifying Families - Autodesk Revit Architecture 2015 Essentials - page 155

4. Activate the Exterior elevation view from the Project Browser window
by double-clicking the Exterior elevation view (Figure 6.21).

Figure 6.21 Reference planes and dimension parameters

Reference planes (displayed as green dashed lines) serve as guides
that allow the geometry to flex. As you can see, the window geometry
has not been directly assigned to dimension parameters. Instead, the
parameters are associated to the reference planes. The window geom-
etry is then associated to the planes. This is the preferred method for
constructing family geometry.

5. Go to the Create tab's Datum panel, and click the Reference Plane
tool. Draw a horizontal plane around the midpoint of the window.

6. Go to the Modify | Place Reference Plane tab's Measure panel, and
click the Aligned Dimension tool. Create a continuous dimension
between the two outermost horizontal reference planes and the new
plane you created in step 4. Click the temporary EQ icon that is active
when you select the dimension just created to establish an equality
constraint (Figure 6.22).

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No matter how the
window height
changes, the new
reference plane will
remain centered.