BIM geospatial coordinates

Revit files (RVT) from Autodesk Revit software and Industry Foundation Classes (IFC) format files use 3D Cartesian coordinate systems that locate data at fixed coordinates. BIM coordinates are not inherently geographic locations; instead, they are locations relative to a simple geometric origin (0,0,0).

Revit file coordinates

Although you can create BIM data where the x,y coordinates correspond to a defined geospatial coordinate system, the data must include the Esri coordinate system definition in the form of a PRJ file for the data to be positioned correctly in ArcGIS Pro.

In Revit software, there is a parameter called Geospatial Location. Despite its name, this information is insufficient to establish the geospatial position of the BIM model. However, this geospatial location information can be inspected from the BIM File Properties user interface and may be useful in helping you establish a BIM model's general location.

In Revit software, the model coordinates used for geometry in the file can be drawn to a geospatial coordinate system definition. You can use the BIM File Properties user interface from the context menu of the Catalog pane to inspect the display units and other file properties before adding Revit data to ArcGIS Pro to ensure the selection of a proper coordinate system that matches the linear display units of the file. You can use workflows in Revit software to establish coordinate values for models, such as the Specify Coordinate at Point tool, to establish geospatial coordinates. Based on BIM project requirements or other factors, BIM data may be created with coordinates corresponding to a defined geospatial coordinate system. In these cases, you must georeference the BIM data to position it in ArcGIS Pro.

IFC file coordinates

You can create the coordinates of geometry in IFC files with linear units and coordinate values that correspond to a defined geospatial coordinate system. If a PRJ file is included that corresponds to that coordinate system, the data is properly positioned in ArcGIS Pro.

Like other CAD and BIM data, if the coordinates of the file do not correspond to the coordinates of the assigned coordinate system PRJ file, you must create a WLD3 world file containing the required coordinate transformation or include it to properly position the data. Generate a world file using the provided tools for georeferencing BIM data.

BIM data linear units

BIM software allows you to create, store, and display data at various scales including feet, meters, inches, and millimeters. ArcGIS defines coordinate system definitions to ensure proper global positioning with linear units typically in feet or meters. The linear units of the selected PRJ coordinate system definition file must agree with the linear units of the BIM data.

Revit file linear units

Autodesk Revit software stores all of the coordinate data in the Revit RVT file as feet. The Revit model author can set the display units of the model when working with the data. This linear display units setting is read by ArcGIS Pro and is used to determine whether the data needs to be scaled to fit the chosen PRJ file. If the display units are in inches or feet, the model coordinates of feet are scaled to feet. If the display setting is millimeters or meters, the model coordinates of feet are scaled to meters. The linear units of the assigned coordinate system definition (PRJ) file must match the display units setting of the Revit model, either imperial or metric.

IFC file linear units

The linear units of IFC files are specified by the authoring software chosen by the file author. The linear units of the IFC file are stored in the IFCUnitAssignment property, which you can inspect on the General option of the BIM File Properties dialog box. ArcGIS Pro properly scales the IFC file geometry according to the specified units.

Geospatial coordinate system PRJ files

By default, RVT or IFC files do not contain Esri coordinate system information to define a coordinate system, so an ancillary PRJ file must be included. The Esri undefined coordinate system is assumed when no coordinate system definition is detected by ArcGIS Pro for a BIM workspace, RVT, or IFC file. When data is added to a map or scene in ArcGIS Pro with an undefined coordinate system, the coordinates of the data are assumed to be the same coordinate system of the current map or scene's coordinate system, which may or may not be correct. It is recommended that you define a coordinate system for all data added to ArcGIS Pro so that it can be properly positioned.

Universal CAD and BIM coordinate system files

To define the same coordinate system for every CAD or BIM file in a file folder, you can rename the PRJ file containing the desired coordinate system to esri_cad.prj, or to any file name that includes a .uprj file extension. Then every CAD or BIM file that does not have an assigned coordinate system will use the universal projection file as its coordinate system. This is useful when all of the files in the folder must use the same coordinate system.

Spatial transformation WLD3 world file

When the coordinates in a CAD or BIM file do not correspond to the included coordinate system due to error or because the file was drawn to a relative position, you can specify a coordinate transformation using an Esri world file. A world file is an ASCII format file with two sets of coordinates that define a linear affine transformation to move scale and rotate the BIM data from where it was drawn to the proper coordinates of the included coordinate system PRJ file.

You can define a coordinate transformation for a BIM file by including a valid world file in the same file folder as the BIM file. The included world file must have the same name as the BIM file but with the .wld3 file extension.

BIM files must have a valid Esri coordinate system PRJ before a WLD3 file can be created since the offset values of the world file must correspond to the specific coordinate system as defined in the Esri PRJ coordinate system definition file.

A CAD or BIM world file WLD3 contains two sets of from-points and to-points to adequately define an 3D affine transformation for BIM or CAD data.

A WLD3 coordinate transformation file is generated as the result of the BIM georeferencing workflow.

Universal CAD and BIM coordinate transformation world file

To define the same coordinate transformation for every CAD or BIM file in a file folder, rename the WLD3 file containing the desired coordinate transformation to esri_cad.wld3, or to any file name with a .uwld3 file extension. ArcGIS Pro applies that coordinate transformation to every CAD or BIM file in that file folder that doesn't have its own specifically named world file. This is useful when all the drawings are accurate to one another and all need to be adjusted in the same way.

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