Shared Coordinates Help Achieve Project Success
Shared Coordinates is not a new feature in Autodesk® Revit®, and yet design professionals may not be fully realizing the potential benefits of leveraging this simple to use and powerful tool. While using Shared Coordinates is not required if working in only a couple of models and if all of the work will remain within the Revit platform, its use is undeniably helpful in situations when combining several Revit models, disciplines, and/or Autodesk platforms.
Simply put, properly using Shared Coordinates ensures alignment of several Revit models. This alignment can be between Revit models only or can be extended for alignment between Revit models and AutoCAD® site/civil content. A previous article written by Jonathan Massaro in the December 2015 issue of AUGIWORLD highlighted the power of using Shared Coordinates and alignment with actual State Plane Coordinates. The question is, can the power of Shared Coordinates still be leveraged if real-world coordinates are unknown at the start of Revit modeling? What if Revit models have already been started, but not yet set up using Shared Coordinates—can Shared Coordinates still be used?
This article will provide answers to both of these questions and provide simple-to-follow workflows for different scenarios depending on the types of content (all Revit versus mixture of CAD/Revit), and whether Shared Coordinates was set up from the beginning or incorporated after models were already started. Before getting into what to do, there is a need to explain some fundamental terminology that will be used for locating the projects in an appropriate coordinate system.
Survey Point, Project Base Point, and the Master Revit File
The Survey Point and Project Base Point are two fundamental points that define the position of geometry in Revit models. A model’s Survey Point marks the origin of its secondary or “shared” coordinate system. Models sharing a coordinate system have the same point of origin, i.e., their Survey Point represents the same point in the physical world. When selected, the Survey Point reads the location of the icon of the Survey Point relative to the physical origin of the secondary coordinate system. In most cases, the Survey Point will have X, Y, and Z coordinates set to zero. This does not mean the shared coordinate system originates at the physical location (0,0,0), but rather that the Survey Point icon is fixated on the coordinate system’s origin.
The Project Base Point, however, can be unique to each model in the same shared coordinate system and is simply an internal point of origin from which spot coordinates can be checked against the site/civil AutoCAD file, if available. When selected, the Project Base Point reads the “true” coordinates of the model in the physical world and is often placed in an intentional location on the model to assist in positioning the project on site. The Project Base Point is used extensively for positioning models at the correct coordinates for proper alignment.
Figure 1 depicts the graphical symbols of the Survey Point and Project Base Point. Note the paperclip symbol located left of each symbol which, once clicked, controls whether the object is “clipped” or “unclipped.”
Figure 1: Survey Point and Project Base Point symbology
Understanding the effects of moving a Project Base Point in a clipped versus an unclipped state is vital to manipulating models of a dynamic project. Moving the Project Base Point in its clipped state should be used when relocating a Revit model on site, as changing the coordinates of the point moves all modeled and annotative content with it. This command has the same effect as the “Relocate Project” command that is built into Revit. Moving an unclipped Project Base Point, however, does not change the physical location of modeled content. This might be used if the Project Base Point needs to be attached to a different physical element of the building or if the reference corner for the building changes.
The term “Master Revit File” is not an official term, but will be used in the article. The purpose of the Master Revit File is to have one file host the coordinates that will be used for sharing across the project. No matter which scenario is followed to set up Shared Coordinates, the initial steps are performed in the Master Revit File and it is the Master Revit File that will be used by the other Revit files for acquiring the Shared Coordinates. The Master Revit File establishes the location of the Survey Point in the physical world and sets the position of the Project Base Point relative to the Survey Point.
Scenario 1: Site/Civil CAD File Available with Actual Site Coordinates
This scenario is ideal for setting up a project’s shared coordinate system. Prior to even starting a Revit model, a CAD file with an established User Coordinate System (CAD’s Shared Coordinate System equivalent) is created and delineates where on the site the future Revit model will be located.
In order to adopt the same coordinate system as the CAD file, the Master Revit File will link the site CAD file into Revit and acquire coordinates from it. When the CAD file is initially linked into the model, likely using the “Auto - Center to Center” option, the coordinate systems are still independent of one another. It is not until the Master Revit File acquires the Shared Coordinates by clicking on the CAD file that the model’s Survey Point will jump to the same point as the CAD file’s User Coordinate System point of origin. Figure 2 depicts a Revit file with a Site-Civil AutoCAD file successfully linked into the project. By using the Acquire Coordinates command in Revit, the Revit project will now set the Survey Point to match the CAD file’s UCS point of origin.
Figure 2: Acquiring coordinates from linked AutoCAD file
Once the Master Revit File successfully acquires the Shared Coordinates from the CAD file, the Project Base Point can be aligned to the point previously delineated on the site file by manually entering the X, Y, and Z coordinates into the clipped Project Base Point’s properties. Doing so secures the model’s position on the site plan and provides a starting point for modeling physical content. It is advantageous in model coordination and site layout for the Project Base Point to be attached to a known, referenceable element of the model. For example, the NW exterior corner of the concrete foundation wall.
Now that the Master Revit File has adopted the CAD file’s shared coordinate system, all subsequent models need only to interact with the Master Revit File to establish the same system in their own models. Each discipline’s Revit model will link in the Master Revit File, acquire its Shared Coordinates, and locate the clipped Project Base Point on the appropriate reference corner of the linked-in model. If these steps are taken for each Revit model in the project, if any given Revit model links in other models using the “Auto - By Shared Coordinates” option, all modeled content will align accordingly without requiring manual manipulation of the linked-in files.
Scenario 2: No CAD File Available for Revit Project Setup
Due to the expedited nature of some projects, the Scenario 1 detailed above is not always possible. Sometimes Revit modeling must begin before a geo-located CAD file is available. If this is the case, a very similar procedure can be followed, although one that eliminates the initial step of communicating with a CAD file.
When the Master Revit File is created, the clipped Project Base Point will be given arbitrary coordinates, e.g., (10, 10, 10) off of which the content can be modeled. All other Revit models can then acquire coordinates from the Master Revit File, establish the same Project Base Point on the designated building element, and begin modeling.
Scenario 3: Enabling Shared Coordinates when Revit Models Already Exist
In both of the scenarios outlined above, the decision to use Shared Coordinates was made before the Revit models were created. As can be imagined, making the decision in favor of Shared Coordinates at the start of the project leads to the most straightforward way of correctly implementing the feature on a project.
Unfortunately, real life gets in the way of ideal project conditions more often than not. Is there any way to implement the benefits of Shared Coordinates if models have already been created that were not set up to use them? Fortunately, not only is the answer to the question a resounding “yes,” but the method for implementing Shared Coordinates post-model creation is actually pretty simple with the following four-step procedure.
- Prior to the start of acquiring coordinates from the Master Revit File, each model needs to have its unclipped Project Base Point moved to the same designated element of the linked Master Revit File.Note that this step assumes that each model has already linked to the Master Revit File by other means (Center to Center or Origin to Origin) and is already properly aligned with it. Also note that the Project Base Point’s coordinate values are irrelevant at this stage because the coordinate system is yet to be shared between models.
- The Master Revit File now establishes the coordinate system by following the instructions of either Scenario 1 or 2, which were described earlier. The previously placed clipped Project Base Point will have its coordinates changed at this stage to match the desired physical coordinates.
- Once the Master Revit File’s position is saved, other Revit models can then reload the link to the Master Revit File and acquire its coordinates as previously described. Note that the Project Base Point must be clipped prior to using the Acquire Coordinate command.
- Without requiring any manual manipulation, the coordinates of the clipped Project Base Point in each model will then be automatically updated to match those of the Master Revit File.
Since the position of the linked models relative to one another has already been established prior to sharing coordinates, acquiring the coordinates does not affect how the models align; rather, it simply changes the value of the Project Base Point to read its position relative to the new location of the Survey Point.
Figure 3 graphically demonstrates the steps described above.
Figure 3: Process to acquire coordinates in an existing Revit model
Taking the Models Beyond Revit
With properly implemented Shared Coordinates, issues with alignment of multiple Revit models should be a problem of the past. Following the instructions outlined above for one of the three scenarios or developing a similar workflow to meet the needs of particular projects should help to eliminate problems with multi-model projects.
Importing Revit models into model coordination platforms such as Navisworks® is a very simple and straightforward procedure if the imported models are already aligned with each other. In fact, most users who have tried using platforms such as Navisworks without properly aligned models have likely found it nearly impossible to use the software without first aligning each of imported models to some set of coordinates.
Exporting Revit models into an AutoCAD file for inclusion in a Site/Civil file is also much simpler if the models are already aligned to each other and to the coordinates used by the CAD file. Note, however, there is one key step that must be done during the export procedure to assure that the shared coordinate system it communicated through the CAD file. For each view to be exported, change the Coordinate System Basis to “Shared” in the DWG/DFX Export Setups window. Figure 4 shows where to change this setting.
Figure 4: How to change CAD export setting from Revit
Shared Coordinates: Easy to Implement and Powerful to Use
Hopefully after reading this article, the concept of using Shared Coordinates should be a little less daunting to those who are unfamiliar with it. In fact, hopefully Revit users will see not only how useful Shared Coordinates can be, but also how relatively easy it is to set up.
In a world where designers and engineers have finite schedules and budgets in order to get projects designed and delivered, spending less time with the semantics of project setup and subsequent adjustments will allow more effort to be exerted on the key design processes of collaboration and coordination, thus leading to better designs and more successful projects.
