Publishing Revit files with known global location

Revit Coordinate Systems

Revit does not have the option to directly specify and define a coordinate system*) and therefore locating projects in real-world conditions for iTwin is relying on the Revit Location settings.

*) Revit can work with imported GIS files defining a surveyed location.

Project set up

Site Location

Establish site location and shared coordinates in Revit.

Prerequisites

  • Latitude and Longitude
  • XY / Easting and Northing to define Revit Project Base Point
  • Revit Survey Point and chosen location

Example:

Lat / Long: 51.481915, -0.136461

Translated to UK**) OS grid: X(E): 529500 / Y(N): 177531 (metres)

**) refer to country specific coordinate systems for locations outside the UK.

Revit 2020

Revit 2020 can now displays the Internal Origin which helps establishing the project location and Autodesk recommends not to be more than 16km away from the Internal Origin.

  • Use Specify Coordinates at Point to define the location of the Project Base Point.

Figure 1 - Revit - Specify Coordinates at Point

  • Do not drag the PBP to a specific point.
  • For reference, the Survey Point can be located at 0,0 – this will allow measurements in iTwins, based on OS coordinates.
  • Set the Angle to True North and set the elevation.

Figure 2 - Revit PBP

Revit Project Base Point with local X and Y values using a local coordinate system.

This set up will also ensure positioning of Revit files in AutoCAD at survey locations (OS or topographical surveys). It will also ensure that the geometry is not too far away from the internal origin, which often can lead to increased inaccuracy and results in persistent Revit warnings.

A quick export with Shared Coordinates to DWG and opened in MicroStation or AutoCAD can verify the location.

Figure 3 - Revit Export

Revit Location

This is the most important aspect in order to successfully connect Revit files to iTwins. This setting isn’t too critical in a Revit only workflow but becomes important when a global positioning is required.

  • X/Y coordinates alone don’t have the capability to globally position a project and that is where the latitude and longitude become useful.
  • The Location settings can be found in Manage -> Location -> Location Weather and Site.
  • The Revit default location, when creating a new project file – as shown in this example is often somewhere outside Boston.

Figure 4 - Default Revit location and corrected location

Location settings can be found and modified in Manage-> Location.

  • Define the location by selecting Default City List and enter the lat / long coordinates.
  • Click OK and open the dialog again to verify the settings.
  • Check that the pin is pointing to the correct location.

Figure 5 - Revit - Manage / Location settings

Please note: Any location / survey information must be verified by a qualified person.

It is also possible to acquire the location through a GIS file created from AutoCAD. This requires the use and knowledge of AutoCAD and its geographic location settings. But in general, a location is selected on a map and then stored within a DWG file. This file can then be referenced into Revit file and coordinates can be acquired.

There are multiple Revit workflows available describing the setup and use of shared coordinate systems and location settings. To discuss all would go beyond the scope of this document and further advice can be found on the Autodesk website.

Figure 6 - PBP matched to Project Location

It is important to note that latitude and longitude will then be aligned to the Revit Project Base Point (PBP). The asset will be positioned with its specified Project Base Point matching the latitude and longitude.

This file has now the correct settings and can be positioned at its true location.

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