Spatially Aligning Revit models

Correctly geolocated iModels can provide additional benefits to a model coordination workflow. Not only can the background map provide more context to the model, measuring coordinates and sharing this information can be valuable for model review tasks.
To take advantage of an iModel's capability to work in a multidisciplinary environment and with various other source files and formats, it is important to correctly align Revit models.

However, there are cases where after successfully connecting a Revit file to an iModel the result is not as expected.

• the file is situated near Boston or your nearest capital city
• the file is slightly offset from the expected location leading to inaccuracies
• or in extreme scenarios where multiple files are located very far apart from each other the entire globe is visible and models are scattered around

In all these cases this is usually caused by missing, incomplete or wrong location information within a Revit file. Prior connecting Revit models it is important to check and verify spatial settings, and if required correcting and adding missing information.

Where it is not feasible to modify source files or no other design applications are available an alternative workflow should be considered.

To successfully geolocate Revit models, a combination of latitude and longitude and / or local grid coordinates will be required. Some of the suggested geolocation methods will also require using other design applications such as MicroStation or Civil3D alongside Revit.

Disclaimer

All described scenarios and workflows are entirely hypothetical and might not reflect a company's tried and tested approach to geolocation and setting up Revit models.
Obtaining global location information requires experience, and it is essential to consult a qualified surveyor.
All described scenarios are only intended for training purposes and the user must independently set up their preferred method.

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Starting a new project

It's always best to have the project location set before starting a new project. Correcting geospatial information later, especially for multiple files, can be time-consuming and, in some cases, might not always be possible. Always include the location information in your project template file and project execution plan. Ensure every project participant is following these standards. Although Revit can link files using various methods – this might not always work with an iTwin.

Geolocating Revit models

There are two key methods to geolocate a Revit model in iTwins.

• Using Revit latitude and longitude values
• Using an external geolocation file

In both cases, a user must have precise coordinates and knowledge of the project requirements.

This needs to consist of

• Local X and Y coordinates
• The spatial location of the site, either a global coordinate system or
• knowledge of latitude and longitude
  

As an absolute minimum, the user should know where the project is located. Most of the required information can be obtained externally. Be aware that incomplete information might not lead to a 100% accurate positioning. In ideal circumstances, a professional surveyor should provide geolocation information for the project.

In cases where the use of an iTwin is considered at the onset of a project, it is important to establish correct geolocation information as early as possible.

Setting the location in a Revit template file and sharing the geocoordinates as a project requirement within a project execution plan can further simplify the synchronization process and prevent issues later. All project participants should be encouraged to follow set guidelines. A good model manager will ensure that all project requirements are adhered to.

It is important to adhere to Autodesk's recommendations, and an understanding of Revit's coordinate systems is necessary.

Scenarios

There are a multitude of potential scenarios.
Often an already completed project model is positioned at an incorrect location in iTwins. In these cases, the Revit models will have to be adjusted.

Questions to ask

• How do I best set up my Revit models at the onset of a project?
• Fixing: Is my Revit file correctly positioned when connecting to an iModel?
  • It's out by a large distance?
  • It's only slightly offset?
• Not allowed: Can I modify or change anything on the Revit models?
• Is there certain information missing or incorrect? i.e.:
  • No latitude and longitude set or unknown?
  • Are the project base point and survey point not used correctly?
  • Unknown location or coordinate system?
  • Large distances to internal origin?
• Worst case: What if I don't have access to Revit / or any CAD application?

Prerequisites

What is required to update Revit models to achieve correct geolocation within an iModel?

• Bentley iTwins, Revit knowledge (admin / manage), understanding of global coordinate systems, use of MicroStation and / or Civil3D
• Access to design applications, Revit, MicroStation, Civil3D

Analyzing a Revit model

Unlike MicroStation or Civil3D, Revit does not have the capability to work with a true global coordinate system (GCS). The project location is defined through local coordinates based on northings (Y) and eastings (X). However, a global project location can be specified based on latitude and longitude. This can be set within the Manage – Location – Location and Site menu. Setting these coordinates to a defined location can help to geolocate the Revit file.

How to verify the location information

What makes a 'good' Revit file, which will achieve correct geolocation?

Latitude and Longitude

The first thing to check is the Location and Site setting.

• Open the Manage tab
• Click on Location
• Select the Location tab
• Check that the Define Location by dropdown menu is set to Internet Mapping Service
• Visually check the map location
  • Typically, there are two default locations, west and south of Boston indicated with a marker
  • Depending on the template file used, the marker can also be placed in your nearest capital city
    
  • Sometimes the marker can also be set to a company's HQ
    

Image 1 - Location marker 

• You can use Google Maps to compare the set location with coordinates close to the actual project location

Image 2 - Real world location vs model location

• If the location matches, you are most likely dealing with a Revit file which has been set up correctly and it can be used to connect to an iModel
• If they are vastly out – the location will have to be adjusted

Not only can the correct position be used to spatially align iModels, but the correctly set location is also used when exporting to IFC files, helping to fulfil the project requirements.

Survey Point

The Revit Survey Point

Image 03 - Revit SP

To check the SP please ensure that it is visible. Visibility settings can be changed in the Visibility / Graphic Override menu.

https://help.autodesk.com/view/RVT/2023/ENU/?guid=GUID-81CB0DD4-DF6E-43A3-AADA-DABC5ED30C6F

"The Revit survey point is a coordinate point that is used to position objects in a Revit model. It is important to understand how the survey point works to create accurate and consistent models.
The survey point has three components:

• The X-axis: This axis runs east-west
• The Y-axis: This axis runs north-south
• The Z-axis: This axis runs up and down

The origin of the survey point is the point at which all three axes intersect. This point is usually located at the centre of the building site.
When creating a new Revit model, the survey point is automatically placed at the origin. However, the survey point can be moved to any other location in the model. This can be useful if creating a model that is aligned with a specific real-world location.
The survey point is a powerful tool that can be used to create accurate and consistent Revit models. By understanding how the survey point works, it can be used it to improve the quality of the design model."

Considerations

• Click on the survey point and check that the coordinate values are NOT set to 0,0 AND are positioned a large distance away from the model elements. This will 'pin' the flat working plane at this point and offsets the entire project by the model's location, leading to inaccuracies

Image 4 - Survey Point

• The SP in combination with the latitude and longitude will be used to position the model
• In case they do not share the same or matching coordinates, the model placement will not be exact
• Local grid coordinates can be 'converted' to latitude and longitude using a global coordinate system

Image 5 - Coordinates converted using a GCS

Try it at:

https://www.engineeringtoolbox.com/utm-latitude-longitude-d_1370.html

https://coordinates-converter.com/

https://www.latlong.net/lat-long-utm.html

Project Base Point

The Project Base Point (PBP)

Image 6 - Revit PBP

To check the PBP please ensure that it is visible. Visibility settings can be changed in the Visibility / Graphic Override menu.

https://help.autodesk.com/view/RVT/2023/ENU/?guid=GUID-D4358965-4574-4C5F-9430-9ECD63BA847E

Considerations

• X and Y values are not important for the correct placement but should be near the model elements
• Elevation will be used to determine the placement height, but this also depends on the modelling method used
• The angle to true north will be used to establish the model rotation

The PBP is not critical for positioning a model accurately, but it is recommended to establish meaningful project coordinates to aid with project coordination.

Internal Origin

The internal origin does not directly influence the geolocation process. As generally recommended, all model elements should be nearby the internal origin. Objects positioned too far away from the internal origin can result in inaccuracies and errors.

Geolocation Methods

The following sections describe in detail how to best configure Revit models to achieve perfect geospatial alignment.

Links to Wiki articles:

• Publishing Revit projects on its own Publishing Revit project models
• Using a MicroStation geolocation file  Using a MicroStation geolocation file to publish Revit projects
• Using a Civil3D geolocation file  Using a Civil3D geolocation file to publish Revit projects 

 Share your feedback and vote on which data types or formats we should document next here.