Building information modeling

Building Information Modeling (BIM) is a process for generation and management of physical and functionnal features of places. The main exchange format for BIM is IFC. Other formats, such as Revit allow creation and manipulation of BIM data.

HOOPS Exchange allows you to read BIM data from any IFC file. The BIM API is available from the A3DSDKBim.h header.

Please note that BIM Data are not part of PRC specifications. As such, the only way to serialize them is by using A3DAsmModelFileExportToIfcXMLFile().

Accessing the BIM Data

Once a model file is loaded, the entry point for BIM data is located within the instance of A3DAsmModelFileData:

typedef struct {
// ...
A3DBIMData* m_pBIMData;
// ...
} A3DAsmModelFileData;
Note
BIM data reading is only available with IFC files and must be toggled on by setting A3DRWParamsIFCData::m_bReadRelationships to A3D_TRUE.

A3DBIMData is a standard entity type (A3DBIMDataData/A3DBIMDataGet()). Within the A3DBIMDataData structure, all BIM-related types are abstracted away using the A3DBIMRoot entity. This means any A3DBIM* entity can be used as an A3DBIMRoot entity (A3DBIMRootData/A3DBIMRootGet()). Specialized data and getters are available according to the type.

Getting BIM relationships

BIM relationships handle the various relationships of objects within a model. The list of all relationships are contained within A3DBIMDataData::m_ppRelationships, a standard array of A3DBIMRelationship entities.

To query the actual type of the relationship, use A3DEntityGetType on the array element. Then, call the specialized data function according to its type. The following example focuses on the Rel Aggregates relationship:

void traverse_aggregates_rel(const A3DBIMDataData* bim_data)
{
A3DEEntityType entity_type = kA3DTypeUnknown;
for(A3DUns32 rel_i = 0 ; rel_i < bim_data->m_uiRelationshipSize ; ++rel_i) {
A3DEntityGetType(bim_data->m_ppRelationships[rel_i], &entity_type);
if (entity_type == kA3DTypeBIMRelAggregates) {
A3DBIMRelAggregatesData aggregates_data;
A3D_INITIALIZE_DATA(A3DBIMRelAggregatesData, &aggregates_data);
A3DBIMRelAggregatesGet(bim_data->m_ppRelationships[rel_i], &aggregates_data);
// Use rel aggregates data
A3DBIMRelAggregatesGet(0, &aggregates_data);
}
}
}

All relationship are represented as pairs of relating and related elements. They either describe one-to-one or one-to-many relationships where the relating element is m_pRelating and the related elements is an array where size is m_uiRelatedElementSize and the pointer is m_ppRelatedElements. Both relating and related entity types depend on the relationship. In the case of a one-to-one relationship, m_uiRelatedElementsSize is always 1 and m_ppRelatedElements can be used as a single pointer.

All relationship entities strictly follow the API convention where the data EData of an entity E can be retrieved with a call to EGet(const E*, EData*).

Rel Aggregates

Entity Entity enumeration type Relating type Related type
A3DBIMRelAggregates kA3DTypeBIMRelAggregates A3DBIMObjectDefinition A3DBIMObjectDefinition

The aggregation is a one-to-many relationship representing a whole/part composition. In this relationship, the related elements is a list of A3DBIMObjectDefinition entities that makes a whole: the relating element A3DBIMObjectDefinition.

Rel Connects Path Elements

Entity Entity enumeration type Relating type Related type
A3DBIMRelConnectsPathElements kA3DTypeBIMRelConnectsPathElements A3DBIMElement A3DBIMElement

This one-to-one relationship provides connectivity information between two path-based elements.

Rel Contained in Spatial Structure

Entity Entity enumeration type Relating type Related type
A3DBIMRelContainedInSpatialStructure kA3DTypeBIMRelContainedInSpatialStructure A3DBIMSpatialStructureElement A3DBIMProduct

This relationship description assign elements to specific levels of a segmented spatial project structure. It is a one-to-many relationship.

Specializations of the relating elements are available:

Rel Fills Element

Entity Entity enumeration type Relating type Related type
A3DBIMRelFillsElement kA3DTypeBIMRelFillsElement A3DBIMOpeningElement A3DBIMBuildingElement

This one-to-one relationship describes an opening element (the relating type) and another element that completly or partially fills it.

Note
To read opening elements, A3DRWParamsIFCData::m_bReadOpeningElements must be set to A3D_TRUE.

Rel Space Boundary

Entity Entity enumeration type Relating type Related type
A3DBIMRelSpaceBoudary kA3DTypeBIMRelSpaceBoudary A3DBIMElement A3DBIMSpace

This one-to-one relationship describes a space in an element using boundaries. The relating element is the space itself, which is delimited by the related element.

Rel Voids Element

Entity Entity enumeration type Relating type Related type
A3DBIMRelVoidsElement kA3DTypeBIMRelVoidsElement A3DBIMOpeningElement A3DBIMElement
Note
To read opening elements, A3DRWParamsIFCData::m_bReadOpeningElements must be set to A3D_TRUE.

The rel voids element describes an opening element that created a void in a building element. It is a one-to-one relationship.

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