by Dennis Collin
A common question from Revit users is how to make Revit families or is it possible to import geometry from 3rd party modelling products and convert them into Revit components.
Creating a parametric family can be quite an involved process, especially if the component requires bespoke parameters and requires parametric properties containing nested parts and look-up tables. However, in many cases it is enough just to have a ‘static’ part that is of a correct category. This element might be already modelled in another product with its geometry saved in another format like a 3DM (Rhino), SKP (SketchUp), (STP) Step file or (SAT) ACIS file.
Fig 1. When creating Revit content, choosing the right family template is key!
When creating a component family, it is vital to ensure that the element is not just set to a correct category, but also a typical behaviour like snapping to a suitable host reference like a wall, floor or ceiling or a free-standing component. The template will also contain potentially useful parameters such as its offset above a floor.
If opting to import geometry from a 3rd party file format, then the Import CAD geometry can be used, and the file format options can be used as shown in the figure below.
Fig 2. Depending on the Revit version used, other formats may be available.
Once confirmed, the geometry should appear in the family component. This component should be appropriately named and saved in a suitable location.
Fig 3. Imported CAD (3DM) data in Revit shows the resize option as disabled unless it’s a DWG or DXF format.
When importing geometry from other formats, Revit will look at the incoming file units and will scale the geometry accordingly to Revit’s typical working unit (usually millimetres). Unfortunately, experience shows that elements imported from external sources often don’t have their units specified properly and as a result elements may come in at the wrong size in Revit. This can cause a headache as Revit will not permit the scaling of non-DWG formats!
Fig 4. Whether producing 2D drawings or 3D components, the defined units are critical when sharing data.
Whilst Revit does have a resizing tool (or scale), it is limited to only resizing elements from certain file formats. These include DWG, DXF formats, but not Rhino (3DM), SketchUp (SKP) ,Step and SAT files formats. If selecting elements from those files, the resize command is greyed out (See Fig 3). The best approach is to revisit the original program that authored these files and ensure that the units are specified correctly. Unfortunately, conceptual units like ‘Unitless’ do not help when trying to translate geometry into other programs!
Fig 5. AutoCAD can open a wide variety of files including 3DM, SAT, IGES and Stp files.
If the original software is not available, it is possible to use AutoCAD to convert the file to a DWG format. Not only can geometry be re-sized but also correct file units can be assigned to the geometry ensure the part will size correctly within the Revit family. AutoCAD can open a wide range of file formats. Elements can be re-sized in AutoCAD, with the correct units set and then saved as a DWG file for importing into Revit. These drawings can be audited and recovered if necessary to ensure that the model geometry opens in Revit cleanly.
Fig 6. Most Revit component families should be sized less than 1MB!
Care should also be taken with the level of modelling detail. Ultimately a good Revit family should typically be sized under a megabyte (<1MB). If this aspect is not closely monitored Revit project performance can be compromised. If this cannot be achieved consider remodelling the element in Revit, it may also be worth purging any superfluous data in the family and its nested components to ensure that the file size is at a minimum and performance is maximised.
Creating Revit families is just one of the training courses that we offer. Visit our Arkance UK site to get an overview of the courses on offer and talk to one of the team for dates and availability. We are here to help!