Attributes

Which problem is addressed by attributes?

To parametrize simulation models, different types of parameters are needed. A BIM model and specifically an IFC model offers multiple sources for the requested information. Let’s assume that we need the net_area of a wall. This information can either be obtained from:

  • the official IFC specified QuantitySet Qto_WallBaseQuantities/NetSideArea

  • the unofficial, but typical in ArchiCAD used BaseQuantities'/NetSideArea

  • any other PropertySet where the BIM modeller might have stored the information

  • the calculation of the Space Boundary area of the wall

  • nowhere, because the information simply does not exist in the model (might not be the case for this example)

To resolve this problem of multiple available sources and even parameters which will be not included in the BIM model at all the Attribute system provides a solution.

Concept / How does it work?

Simulation required informations that are potentially available in the BIM model are stored in an Attribute at the corresponding element.

E.g. the already mentioned net_area is implemented by the following lines in the the class OuterWall:


net_area = attribute.Attribute(
    default_ps=("Qto_WallBaseQuantities", "NetSideArea"),
    functions=[BPSProduct.get_net_bound_area],
    unit=ureg.meter ** 2
)

This way bim2sim knows where to look for in the IFC file and which function to use if no information exists in the IFC file. Also the unit in which the value should be stored is provided as m². See _get_value function of attribute documentation for more detailed description which other ways are implemented to obtain a value.

How are the attributes managed?

To manage the different attributes every bim2sim element instance owns an instance of the AttributeManager which is stored under element.attributes. This manager manages the values and current status of the Attributes.

If an information can’t be obtained by the implemented ways in _get_value function of attribute of attribute its status will be changed to NOT_AVAILABLE. As some information are mandatory to parametrize a simulation model, we implemented the concept of Decisions which is basically a structured way to obtain information from the user. To make sure that all relevant information exists, a parameter can be requested. This way a Decisions will be created if the status of the corresponding attribute is NOT_AVAILABLE.

// todo: flow chart with mermaid. To use mermaid: https://github.com/mgaitan/sphinxcontrib-mermaid#markdown-support

The AttributeManager uses the status of each attribute to store if an attribute was already requested. To trigger all decisions for the already requested attributes to finally obtain the corresponding values the final tasks before exporting to a simulation model should always trigger the get_pending_attribute_decisions function of element. This implementation was made to bundle the decisions at the end of the process if possible.