The information in this guide is derived in part from Revit's documentation and applies to Revit 2020.1 and higher.
Georeferencing allows you to establish the relative positions of the different types of models included in a project. This process is one of the most important steps in setting up a project - if not the most important. Indeed, teams and stakeholders are required to work in several software programs, on models or files that may need to be linked to ensure consistency and accuracy.
Revit models can be linked using two systems: internal coordinates and shared coordinates.
BIM Track also requires the use of shared coordinates in order to position models in the correct position when they are published to the viewer.
This guide explains how the different coordinates points must be used to set up a shared coordinates system in Revit so that project models align correctly in the BIM Track viewer. It contains the following sections:
Coordinate points overview
Here's an overview of the various coordinate points and how they should be used to ensure a smooth display in the BIM Track viewer.
If you are new to Revit’s positioning features, click on the links provided to learn more about the points introduced below. If you are ready to proceed to the shared coordinates setup step, see Set Up Revit Shared Coordinates.
Centre of the Earth
The centre of the Earth corresponds to the 0,0,0 system position for the shared coordinates system and is the point that BIM Track uses as a reference for positioning models in the BIM Track viewer.
When you create the site (host) model or any other model in Revit, the centre of the Earth, the project base point and the survey point are placed at the internal origin by default.
The project base point and the survey point display only in the site plan view and are initially located at the same position. The internal origin is off by default in all views. To make them visible in another view, open the desired view, click View tab > Graphics panel > Visibility/Graphics.
Unlike the other points, the centre of the earth (0,0,0) is not represented by any icon.
The survey point is a real-world relation to the Revit model. It represents a specific point on the Earth, such as a geodetic survey marker or a point of reference based on project property lines.
The survey point is normally the geodetic marker on a surveyor's coordinate system, which is provided to the engineer to determine the coordinates of the site in relation to the centre of the Earth. The survey point serves as a reference point on the coordinate system within a radius closer to the site than the origin of the Earth. It will be useful, among other things, to position the building in relation to this reference.
If you are the person in charge of georeferencing the site model, follow the steps in Workflow: Positioning. For the first step, we recommend that you acquire the coordinates of a DWG (georeferenced) file from a surveyor into the site model, or that you manually integrate the values in order to geolocate the project using the geodetic information transmitted.
When defining the survey point of the site model (step 2 in Workflow: positioning), make sure the survey point is unclipped and then drag it to the desired location in relation to the centre of the Earth, near the project.
In the model, the coordinates of the survey point change to reflect its new location in relation to the centre of the Earth and its new proximity to the project base point.
Moving the survey point in relation to the centre of the Earth will have no impact on the position of the centre of the Earth, which will remain at the right location (0,0,0) so that the project is correctly located on the Earth. The shared coordinates thus correspond to the location of the site in relation to the 0,0,0 point.
Once the survey point is defined, it should be kept unclipped to avoid moving the centre of the Earth if the survey point is moved inadvertently. Then, it must be pinned by clicking the Modify tab > Modify panel > Pin.
Project base point
The project base point is used to create a reference for positioning elements in relation to the model itself. It can be used as a reference point for measurements and references across the site. The location of this point does not affect the shared site coordinates. However, the model must be created close to the project base point and it must be located at a point that makes sense in the model (usually at the intersection of two grid lines or at the corner of a building).
To ensure that the project base point is not moved, pin it (Modify tab > Modify panel > Pin).
The internal origin is the starting point for the internal coordinate system, which provides the basis for positioning all elements in the model. Its location can not be move, it is the earth that moves below the position of the internal coordinates.
In order to avoid undesirable graphical behavior in the viewer, the internal origin must be at a maximum distance of 32 kilometers (20 miles) from the model geometry.
If the site position is moved or changed, the issues created with the first position of the shared site will remain at this location. The spheres are positioned relative to the centre of the earth, so if the site moves relative to the centre of the earth, the spheres will remain at the initial location. It is therefore essential to do the georeferencing right from the start and to avoid moving or modifying the site during the project.
- The survey point and the project base point can be moved freely during the georeferencing process. However, it is recommended to place them close to each other, close to the project.
- When moving the survey point, make sure it is unclipped to keep the position of the centre of the Earth at the 0,0,0 position.
- When moving the project base point, attach it to keep the default overlay of the internal origin point (Revit 2019 and prior versions).
- To ensure that the topography point and the project base point are not inadvertently moved, pin them (Modify tab > Modify panel > Pin).
If you are working in the site model, follow the steps in Workflow: Positioning to establish its position. You can then publish the coordinates to linked building models by following the steps in Set Up Revit Shared Coordinates.
If you are working in a building model file, you can acquire coordinates from the site model. To do so, follow the steps in Set Up Revit Shared Coordinates.