By Dennis Collin
Linking files are a major tool to use when working in a federated model. We need to link files from a range of disciplines for coordination, checking and clash detection purposes. Not just within Revit, but also other packages such as Navisworks and increasingly the BIM360 set of collaborative tools online. By linking files, we can see any changes made just by reloading the latest version.
Within Revit there are an increasing range of formats that can be linked, from CAD files such as DXF, DWG and DGN to Revit files from other disciplines, Navisworks and point cloud data. These, barring a few exceptions, include an option to make use of a shared coordinate system when linking. A shared origin is critical with collaboration to ensure the many disciplines involved are all working in the same place. The shared coordinate system origin within Revit is usually represented by making use of setting the position of the Survey Point marker and true north aspect in a site plan view to reflect the National Grid system.
Fig 1. Option for linking CAD files (in this example a DWG)
Fig 2. Option for linking a coordination model such as a Navisworks NWD
Fig 3. Options for linking a Revit RVT model
For IFC files however, this feature is lacking as there is no option to choose a coordinate system and as a result, when linking or opening an IFC file, the shared coordinate system and origin is not present.
Fig 4. Very simple IFC link dialogue with no option dropdown to choose origin or coordinate system.
To create IFC files from Revit it is a straightforward export process. From the application menu choose EXPORT>IFC and select appropriate options using an appropriate IFC standard.
Fig 5. IFC Export options using OOTB functionality
However, even with the out of the box (OOTB) export function with Revit 2019.2, there is no option to choose or set the coordinate system. The export just sets the coordinates of the IFC file to the project origin which is seldom used and is of no use to anyone trying to assemble a federated model without a lot of unnecessary rework.
However, last year there was a major update to the IFC plug-in which resolves many issues including the option to choose coordinate systems.
The new IFC plug-in, available for Revit 2018 and 2019 will provide additional options to share Revit data in a coordinated IFC format much more easily!
Fig 6. Improved IFC export dialogue options!
Enhanced IFC export options for Revit 2018 and 2019! The coordinate options should be situated under the ‘general’ tab. If it’s not there, install the latest IFC plug-in from the App store.
Linking the IFC file with the new plug-in doesn’t have any import options, but the file is positioned correctly with respect to the specified origin and north point which can be seen in the image below:
Fig 7. Checking a linked IFC file’s coordinates against the original file’s settings.