Dimensions are by definition a measurement of an object in physical space. In Revit, they are annotation elements that can measure the size of components and elements such as height, width and depth. Dimensions also convey an object’s angle, radius, diameter and arc length. They are system families that contain user editable properties. Users have the option to add new dimension types by duplicating an existing dimension type, renaming it and then applying custom properties to it. The new dimension type is then added to the type selector of the Properties palette (see Figure 1).
Permanent and Temporary Dimensions
Dimensions can be permanent and temporary. Permanent dimensions appear in construction documents, details and illustrations. They display information pertaining to a project or a building component. Temporary dimensions, however, aid in the sketching and modeling process. They appear as guides whose values can be changed as building components are being modeled. They also appear when a building component is selected. Temporary dimensions are useful in functions such as the move, copy and rotate commands (see Figure 2).
For example, when a component is selected in a project, its distance from a wall can be changed. This is done by selecting the temporary dimension (see Figure 3), typing a different value and pressing Enter on the keyboard. The location of the component then updates to its new location (see Figure 4).
In a project file, dimensions are used for annotating building elements that go into sheets used as construction documents. They are view specific and can also be used in design development or for in-house purposes.
Dimensions in the Family Editor
On the other hand, dimensions in the Family Editor are used primarily for creating parametric families controlled by dimensions. These dimensional parameters control the shape of a component such as height, width, depth, angle and length. This is done by selecting the dimension and choosing <Add parameter...> from the drop-down list of the Label option in the Options bar (see Figure 5).
This opens the Parameter Properties dialog box where the label can be named in the Parameter Data panel (see Figure 6).
Note: Parameters will be discussed in part 7 of this series.
Before we go any further, here is an at-a-glance illustration of the different styles of dimensions and their parts (see Figure 7). The texts in red are the styles, and the texts in purple are the parts. Study them carefully, and try them out in the Family Editor.
Listening Dimensions
A listening dimension is a form of temporary dimension that appears as an element is being sketched inside or outside the sketch mode. As soon as it appears (see Figure 8), a specific value can be entered right away (see Figure 9), even without selecting the temporary dimension’s value. Pressing Enter afterwards draws the profile at the specified length (see Figure 10).
Listening dimensions look similar to temporary dimensions except that the font is bold. They appear after the first click of any Draw tool in the sketch mode. The dimension values interactively change as the cursor is moved after the first click.
The Dimension Panel
The Dimension panel is located in the Annotate tab (see Figure 11) and consists of five dimension tools:
- Aligned: The Aligned dimension tool places dimensions between parallel reference planes, reference lines, model lines, symbolic lines, lines drawn in sketch mode, parallel edges of components and vertex points of lines or corners of components (selected by pressing the Tab key). To place a single-segment dimension, click the first element and then click the second element. The tool remains active. Moving the cursor at the desired location and clicking a third time on a blank space establishes the dimension. Alternatively, while the tool remains active after the second click, other elements can be selected, thereby creating a multi-segment dimension. To end the multi-segment dimensions, move the dimension string to the desired location and click on a blank space.
- Angular: The Angular dimension tool measures angles between two elements that meet at a common intersection. These elements can be a part of a form or they can be edges from multiple components. The first two clicks select the edges. Moving the cursor at the desired location and clicking a third time establishes the angle of the selected edges.
- Radial: The Radial dimension tool measures the radius of a curve, a circle or an arc. The first click selects the edge to be dimensioned. Moving the preview of the dimension to the desired location and clicking a second time establishes the radius dimension.
- Diameter: The Diameter dimension tool measures the length of a straight line segment that passes through the center of a circle. Its end points are at the boundary of the circle. The first click at the edge of a circle displays a line across the circle with a preview of the diameter value. This line follows the cursor as it is moved to the desired location. A second click establishes the diameter.
- The Arc Length tool measures the length of an arc. The dimensioning process is accomplished with four clicks. The first click selects the edge of the arc. The cursor then turns into a "no" symbol (a circle with a slash in the middle). The second click is at the edge of an element or start or end point of an arc. The third click is made at the opposite edge of the arc. A preview of the dimension follows the cursor as it is placed at the desired location and clicked a fourth time to establish the arc length.
Equality Constraint
Equality constraint is a dimension feature used to maintain equal distance between multiple components and elements such as reference planes, reference lines and model lines. This is applied by clicking the blue EQ (equal) icon that appears on a selected dimension string (see Figure 12).
The EQ icon appears with a red slash. Clicking it removes the slash, spaces the elements equally and replaces the numerical values with EQ (see Figure 13).
Converting a Temporary Dimension to a Permanent Dimension
When an element is selected, the temporary dimensions display a dimension icon below the values (see Figure 14).
When this is clicked, it turns the temporary dimension into a permanent dimension (see Figure 15).
How to Delete a Specific Segment from a Multi-Segment Dimension
Hover the selection cursor on top of the segment you wish to delete then press the Tab key until the segment highlights in blue (see Figure 16).
Click the mouse and then press the Delete key. The segment is deleted (see Figure 17).
Hot Tip: How to Override a Dimension with a Value Different from the Actual Value
Unlike CAD programs, Revit will not allow you to override a dimension value with another dimension value without changing the geometry. However, there are instances in a project where you want to override an actual value with a different value without it affecting the model. You can do this with a trick in which you use text that looks like a dimension value.
Here is how to do it:
Hover the cursor on top of a dimension value until a light-blue border appears (see Figure 18), and then click the mouse.
This opens the Dimension Text dialog box (see Figure 19).
Click the Replace with Text button, and then right click the blank field next to it. Select the Insert Unicode control character option and then select US Unit Separator (Segment separator) at the bottom of the contextual menu (see Figure 20).
The Dimension Text dialog box appears again (see Figure 21). Type a different value in the Replace with Text field. In this case, 15' – 6" will be replaced with 17' – 0" (see Figure 21).
Click OK and then voila! The actual dimension is overridden—or at least appears to be (see Figure 22).
Caution: Please use this technique only as absolutely needed, since the text will give the appearance of a real dimension but, now, it won't change if the model is changed. Consult with your BIM manager before you apply this procedure to your construction documents.
Placing dimensions properly in Revit demands an understanding of Revit’s terms and conventions. Dimensions accurately display the model’s geometry—except when they don’t and a text override is used. Place reference planes as guides before you draw lines in sketch mode. Do the same for components being modeled in the project environment. Detail and model lines can also be used as reference lines in the Family Editor. However, don’t forget to delete them after you model your components. The Dimension Text dialog box contains useful options that let you:
- Replace a dimension with text
- Add a prefix before a dimension value
- Add a suffix after a dimension value
- Add text below the dimension segment line
Taking advantage of these options allows you to annotate your components clearly and accurately.
This is Part 5 in a 10-part series on Creating Loadable Revit Families. For more information, see:
- Part 1: Classification of Revit Families
- Part 2: The Revit Family Editor User Interface
- Part 3: The Ribbon, Quick Access Toolbar, Keyboard Shortcuts and Snaps
- Part 4: How to Use Work Planes in Revit
- Part 5: How to Dimension with Revit
- Part 6: Using Revit Draw and Modify Tools
- Part 7.1: Modeling Basics: The Family Editor Modeling Tools
- Part 7.2: Modeling Basics: How to Create Simple Parameters in Revit
- Part 8: Applying Materials in Revit
- Part 9: Introduction to Revit Conceptual Massing
- Part 10: How to Practice Revit Family Modeling
About the Author
Michael Anonuevo currently works for YWS Design & Architecture located in Las Vegas, Nevada. He is a technical writer, BIM modeler and musician who owns and runs www.littledetailscount.com. Founded in 2009, his website specializes in unique and highly detailed Revit families created in native Autodesk Revit Architecture geometry. Michael is an Autodesk Revit Architecture Certified Professional. He is also an Autodesk beta tester for Revit Architecture. At ClubRevit.com, he regularly writes articles pertaining to Revit families. He also writes product reviews and is a contributing author at AUGIWorld, AECbytes, CAD Digest, revitcommunity.com, and revitforum.org. He is a member of AUGI, Club Revit, the UK Revit Register, the Los Angeles Revit Users Group and the Southern California Revit Users Group.