Import BIM/gbXML Data

DesignBuilder provides interoperability with BIM models through its gbXML import capability. This allows you to import 3-D architectural models created in Revit, ArchiCAD, Microstation and other BIM systems supporting gbXML data exchange.

You can import gbXML from the site or building level using the Import BIM model toolbar icon or use the File > Import > Import BIM/gbXML model. This opens the Import BIM Model dialog. If you are at site level DesignBuilder will require you to create a building first to import the BIM model into.

Unlike the 2-D drawing import which provides only a set of lines for tracing over, importing 3-D BIM data imports the full geometry as blocks with zones, windows, doors and shading surfaces.

Example model imported from Revit into DesignBuilder

Example model imported from ArchiCAD into DesignBuilder

The Import BIM Model dialog has two pages. On the first page you can select the xml file to import. The file must use the gbXML standard data format. Once you have selected the model, press the Next button to move to the second page. For large models there will be a delay at this point while the model is loaded to the dialog. The second page shows a preview of the model along with some controls to control the way the import is to be carried out.

Import Options

View

You can display the preview of the model from various viewpoints. Select from:

• 1-Plan,
• 2-Left,
• 3-Right,
• 4-Back,
• 5-Front,
• 6-Axonometric (3-D view).

gbXML Space and Surface options

The options used to control the import of the geometry depends on the version.

Import priority

This option allows you to define whether the system should prioritise reduction of gaps between blocks or whether to aim to minimise likelihood of open manifold blocks being generated.

• 1-Minimise gaps between blocks where the gbXML surfaces are used to define block geometry. This is the default option as it typically gives the best results for the majority of BIM models imported from Revit and most other BIM applications.
• 2-Minimise open manifold blocks where DesignBuilder works out whether it would be better to use the space or surface data sets based on the criterion that the number of open manifold blocks should be minimised. Open manifold blocks are blocks that are not fully enclosed.

Adjacency tolerance

This is the maximum gap between neighbouring parallel gbXML surfaces that will be interpreted as being an adjacency between 2 spaces. You might enter a value higher than the default 0.01m if the gbXML spaces are separated by large gaps due to thick partitions or ceiling /floor voids being excluded from the gbXML. For example if the largest gap in the between spaces that are to be modelled as adjacent is 0.3m then enter 0.3m here.

The Adjacency tolerance can also be updated after the import from the Advanced tab of the Model options dialog.

Create storey blocks

This option is used to automatically identify stories by grouping adjacent spaces created by extruding from the floor plan with the same upper and lower Z coordinates into single blocks. This has the advantage of making it much easier to later modify internal layouts and it also helps to navigate around large models.

Note: For imported spaces to be grouped into storey blocks, they must all have the same height. Any zones with different ceiling heights will be imported as independent blocks.

Tip: It can sometimes help, especially in lower quality gbXML data sets, to import raw surface geometry exactly as defined in the BIM model. In this case the Create storey blocks setting should be switched off and the Allow open manifold building blocks setting should be switched on.

Import as building blocks

By default this option is selected and the geometric space data will be imported as building blocks ready for use in DesignBuilder modelling. However, you can instead import BIM space geometry as outline blocks by unchecking this option. The outline blocks give an exact representation of the gbXML spaces in the gbXML and this can be useful for diagnosing problems with poor gbXML. For example if any part of a space intersects with another space then it would not be created as a building block, but it could still be created as an outline block to help you identify and fix any possible issues with intersection in the BIM model.

Import thermal properties

If this option is selected then DesignBuilder will any load materials, constructions and glazing system thermal properties present in the BIM model and assign them to surfaces and windows in the model.

Allow open manifold building blocks

Open manifold (non-enclosed) blocks are a special type of block which are only created when models are imported from BIM. They have one or more surfaces missing which means that they are not fully enclosed and this has significant consequences on what can be done with the block in the DesignBuilder modeller and in calculations:

• Radiance and CFD calculations cannot be carried out.
• The boolean operations used behind the scenes to manipulate block geometry are not possible and so only limited edit operations may be performed on open manifold blocks. In particular these operations cannot be performed:
  
  
  • Add surface
  • Drag block face
  • Mirror
  • Divide block using cutting tool
  • Boolean geometry operations.

Tip: Open manifold blocks are shown in a lighter grey than normal closed manifold blocks to differentiate them and their icons in the Navigator have a red outline. See screenshot below.

Because Open manifold blocks cannot use all geometry operations, the orientation of their surfaces cannot be reliably determined from the model and DesignBuilder must rely on the orientation data stored with the surface from the BIM model. This data is not always reliable and so in some cases surfaces are facing in the wrong orientation. The Flip block surface orientation command can and should be used to check and, if necessary fix, the orientation of surfaces in all open manifold blocks.

Import shading plane surfaces

Shading plane surfaces are specially marked in gbXML data and so can be treated separately if required. You can choose to import shading surfaces as planes as part of the import or not using this control. Shading surfaces imported through gbXML will be modelled as 2-D flat shading plane surfaces.

Note: Shading plane surfaces do not have any impact on external CFD analyses.

Tip: You can choose whether or not shading planes will be applied to the model using the BIM Surfaces model option.

Merge co-planar surfaces

If the above Import shading surfaces option is selected then you can choose to either merge any such co-planar surfaces or not.

How does DesignBuilder gbXML Import Work?

The geometric information contained in gbXML includes a collection of surface and space objects which represent the outer and inner volumes of rooms in the parent BIM model respectively. The surface objects are derived from corresponding wall, ceiling, floor etc elements in the BIM and also contain openings for windows and doors. The space objects aren’t native to the BIM system but are identified by users through a manual or semi-automatic process. The result of the spatial identification process is a collection of spaces that are separated by gaps that would be filled in the parent BIM model by the BIM primitives such as partitions, slabs, etc.

Internally DesignBuilder includes 2 different ways to import gbXML data:

• Surfaces where the gbXML surfaces are used to define the block geometry. In well constructed gbXML data sources this data is used to define the outer block geometry. It avoids the need to see gaps between the blocks caused by partition and internal floor thickness. However if surfaces are missing you may end up with surfaces also missing in the DesignBuilder model leading to open manifold blocks which can't be simulated in daylighting and CFD.
• Spaces where surface data is not available the spaces are used as the source of the block geometry.

The DesignBuilder gbXML import works by simply mapping the gbXML space surface geometry to building blocks, one block per zone.

The way to think about the relationship between gbXML spaces and surfaces is that surfaces are those surfaces that define the interlocking contiguous zones that make up the whole building model and the spaces are the inner volume spaces representing the contained air volumes within each zone. So, each internal surface between adjacent zones would generally represent the centre-line between the zones, and the associated record in the gbXML file would reference both zones in the adjacent space field.

Depending on the method used to identify the block geometry they represent:

• In the normal case where DB was able to use surfaces to define the block the External measurements"Geometry convention template is applied to give realistic thickness for block surfaces based on the overall thickness of the surface constructions defined in the gbXML if this option was selected.
• Alternatively if DB wasn't able to find enough surface data to define the block but full space data is available then it uses the space inner geometry and applies the Simple Geometry convention template to give zero thickness for all block surfaces. In this case the building will be made up of a set of blocks defined based on the gbXML inner spaces, possibly with gaps between them due to the partitions and internal floors.

Note: It is important to understand that in both cases the success of the BIM to DesignBuilder data transfer process depends on how well the spatial identification process has been conducted in the BIM system. If there are intersecting or missing spaces in the BIM model then the model imported into DesignBuilder will also have problems.

The adjacency between neighbouring surfaces is calculated within DesignBuilder based on the Adjacency tolerance setting.

Constructions and glazing systems are assigned to surfaces in the gbXML and when the Import thermal properties option is selected in the import dialog the constructions assigned in the BIM program will be assigned at surface level within the imported model.

Shading surfaces in the gbXML are retained and displayed in the imported model. Other surface objects aren't normally required and are hidden after the import has been completed but can be activated as shading surfaces from the Model options dialog, Drawing tools tab.

Note: For models imported through the gbXML mechanism, the windows will always be custom. This is true even when importing a model that had previously been exported from a DesignBuilder model that used the default façade mechanism.

The Revit DesignBuilder Workflow

There is a DesignBuilder add-in for all recent versions of Revit, which can help to ease the workflow when transferring BIM models from Revit to DesignBuilder. The appropriate Revit add-in is installed when you install DesignBuilder.

Note: Ideally the version of Revit you wish to use should be installed at the time you install DesignBuilder. However if this is not the case, you can install the DesignBuilder Revit add-in individually after you have installed the version of Revit you wish to use without reinstalling the whole DesignBuilder application. The DesignBuilder Revit add-in can be installed from the Downloads section of the website. Note that a different add-in is available for each version of Revit. You should ensure that you install the right version. For example if you are using Revit 2019 you should install the DesignBuilder Add-in For Revit 2019.

You can read how to get the most from the Revit to DesignBuilder link in the DesignBuilder Revit – gbXML Tutorial.