The purpose of this module is to facilitate automated detection and retrieval of construction site spatial data from existing Building Information Models (BIM) of the project. Building Information Modeling is an object-oriented approach that enables storing multi-disciplinary information within one virtual representation in order to enhance collaboration between project parties and reduce redundancy of planning and engineering efforts (Schlueter and Thesseling 2009). This module is designed to retrieve from the project’s BIM files the geometric attributes of the construction site, buildings under construction, and buildings rooms. First, the project’s building information model is exported from commercially available design software packages (such as Autodesk Revit) in an IFC 2x3 (Industry Foundation Classes) file format, which is a non-proprietary and interoperable data model of buildings that was developed by the International Alliance for Interoperability (IAI 2010).
Second, an open source dynamic-link library, named IFCEngine.dll (TNO 2009) is integrated in the system to enable parsing the exported IFC file and identifying the geometric attributes of the construction site and buildings under construction, as explained in following subsections.
6.2.1 Identification of Site Boundaries
The construction site boundary is represented by a 2D rectangle that is identified by the coordinates of its four corners. In IFC 2x3 Schema, the construction site is represented using IfcSite entity that may support different geometric representations such as survey points, meshes, solid bodies, and lines. As such, the site boundary coordinates are identified by locating the IfcSite entity and performing the following three main steps, as shown in Figure
6.2: (1) retrieving IfcProductRepresentation entity using the connecting attribute (i.e.
Representation)), which contains all IfcSite geometric representations IfcRepresentation;
(2) looping over these representations of the IfcProductRepresentation using its
“Representations” attribute and selecting the 2D curve representation that has
“RepresentationType” attribute equals Curve2D; and (3) identifying the coordinates of the construction site boundary corners (SiteXmin, SiteYmin, SiteXmax, and SiteYmax) by obtaining the
“Coordinates” attribute of each IfcCartesianPoint entity of Curve2D IfcRepresentation, which is retrieved in the previous step. These coordinates are stored in AMCLOS database to be considered in the generation of site locations grid and the formulation of site boundary constraints that are imposed on all temporary facilities and material storage areas.
IfcSite
Optimal planning of construction logistics in the present AMCLOS system requires the identification of three main spatial attributes of each building under construction: building floors, coordinates of building footprint, and building rooms. First, building floors are represented using IfcBuildingStorey entity that has a decomposition relationship with its building entity IfcBuilding. Building floors are retrieved from the IFC-based model in two
main steps: (1) getting the decomposition entity (IfcRelDecomposes) using the
“IsDecomposedBy” attribute of IfcBuilding entity; and (2) recalling all building floors (IfcBuildingStorey entities) that are linked to the decomposition relationship entity IfcRelDecomposes through its attribute “RelatedObjects”. Three attributes are stored in the AMCLOS database for each floor: “Elevation” (in meters), “GlobalID” (global unique identification string to be differentiated from other entities in the IFC model) and “Name”
(e.g., first floor) that are inherited from its parent entities “IfcProduct” and IfcSpatialStructureElement. Building floors identification is needed to efficiently define spatio-temporal links between each floor construction activities and rooms such as floor partitioning and creation times.
Second, coordinates of building footprint are calculated as the bounding 2D box of all of its building elements as these coordinates are not explicitly modeled in the IfcBuilding entity.
Accordingly, building footprint coordinates are calculated in three main steps: (1) recalling all building components that are represented in the IFC model using subtypes if IfcBuildingElement entity such as IfcSlab, IfcColumn, and IfcWall; (2) obtaining the vertices of each of these building components by using IFCEngine and specialized data structures of Microsoft DirectX 9.0; and (3) calculating the coordinates of building footprint (BXmin, BYmin, BXmax, and BYmax) as the bounding box of all building components using the obtained vertices of each element. Building footprint coordinates are used in the formulation of exterior space overlap constraints between buildings under construction and other site facilities, such as temporary facilities and material storage areas.
Third, the centroid and area of each building room are calculated in order to be utilized in positioning interior material storage areas. Building rooms are represented in the IFC model using IfcSpace entity (subtype of IfcSpatialStructureElement entity), which is used to provide geometric and functional information of interior building spaces that are bounded by building components. First, the centroids of building rooms are calculated using their vertices data using Microsoft DirectX 9.0 data structures, similar to the earlier described building components (i.e., IfcSlab, IfcColumn, etc.). These centroids are utilized in the calculation of interior handling distances between activities workspaces and material storage areas. Second, the area of each building room is obtained by tracking the IFC schema relationships between each IfcSpace entity and its corresponding IfcQuantityArea entity, which contains data on the room area. The area of each building room is obtained in three main steps: (1) IfcRelDefinesByProperties entity is identified for each IfcSpace entity using its
“IsDefinedBy” attribute; (2) “RelatingPropertyDefinition” attribute of IfcRelDefinesByProperties entity is used to retrieve IfcElementQuantity entity that contains a set of physical quantities, such as length, volume, mass, and area; and (3) obtain the set of all physical quantities using “Quantities” attribute of IfcElementQuantity entity and search for IfcQuantityArea entity, which defines the room’s area through its
“AreaValue” attribute. The area of each building room is stored in AMCLOS database in order to be considered during the allocation of interior spaces to material storage areas.
IfcBuilding
Vertices (X,Y, Z) of Building Elements and Rooms