When working with multiple IFC models from different sources, it can be tricky to ensure they’re properly aligned, especially when they use different coordinate systems.
What is IfcMapConversion?
Starting from IFC4, IfcMapConversion is supported. It was introduced to provide the ability to convert geographic coordinates to those used within the IFC model, which is useful when integrating BIM models with Geographic Information Systems (GIS).
In IFC4.3, the support for IfcMapConversion has been further refined, with more specific definitions and applications, allowing it to better handle geographic and project-specific coordinate systems.
BIMcollab Zoom version 9.3 and newer introduces the Georeferencing option that supports the interpretation of IfcMapConversion information to coordinate your models.
To enable or disable this setting, go to Extra> Settings in BIMcollab, on the Model tab, check or uncheck the box for 'Use georeferencing'.
📝 Note: By default, this setting is turned off in BIMcollab.
In some projects, IFC files might contain different georeferencing information. Here are are few common situations and how the BIMcollab Zoom will align your models:
Use case example 1: No models use IfcMapConversion
This will be the case when all models are exported to IFC 2x3.
In this situation, BIMcollab interprets the IfcSite LocalPlacement for model coordination.
Automatic alignment of faraway models
If the IfcSite LocalPlacement of a certain model is very far away (>10km), the model is moved automatically to align with the other models.
This option can be disabled by adjusting your settings file
Tip: You can open an IFC file in a text editor to check its placement information.
Example IfcSite LocalPlacement on the IFC project origin.
Example IfcSite LocalPlacement far away from the IFC project origin.
Use case example 2: Mixed models (some with IfcMapConversion, some without)
If you open an IFC4 (.3) file in BIMcollab Zoom, the feature that automatically aligns far-away models is switched off. This means that if you load a second model that does not have the IfcMapConversion coordination reference in it, it will be shown somewhere far away from the already loaded model, and it will probably not be visible at all.
In such a case, you can either request from the model supplier to add the IfcMapConversion to the model, or you can choose to turn off the georeferencing in BIMcollab.
In that case, the IfcMapConversion in the loaded model will be ignored, and aligning models will be done like in the first use case.
To disable georeferencing, go to Extra> Settings in BIMcollab, on the Model tab, delete the checkmark 'Use georeferencing'
Tip: If you want to know if your IFC file has georeferencing in it, you can open your file in a text editor and look for the following lines:
Example of a location defined by IfcMapConversion.
Use case example 3: All loaded models use IfcMapConversion
In this case, you can turn on the georeferencing checkmark in Settings, and the models should all align.
Additional information
In addition to the IfcMapConversion, BIMcollab Zoom also interprets the WorldCoordinateSystem defined in the IfcGeometricRepresentationContext. Both the IfcMapConversion and the IfcSite LocalPlacement reference the WorldCoordinateSystem information.
Example IfcMapConversion and IfcProject that reference the same IfcGeometricRepresentationContext.WorldCoordinateSystem:
Example of IfcProject that references an IfcGeometricRepresentationContext. WorldCoordinateSystem that’s not (0,0,0):
More information on IfcGeometricRepresentationContext parameters can be found at the BuildingSmart website.
More information on IfcMapConversion parameters can be found at the BuildingSmart website.
IFC information not used by BIMcollab Zoom for model coordination:
Geographic referencing information defined in property sets (for IFC 2x3 file)
RefLatitude, RefLongitude and RefElevation parameter of IfcSite