Data exchange using the IFC standard and BIMserver Laura...

Data exchange using the IFC standard and BIMserver

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Laura Swaine

DT168 MSc in Construction Informatics

5th

December 2012


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Abstract

Building Information Modelling (BIM) has developed for use in the Architectural,

Engineering, Construction and Facility Management (AEC-FM) industry for use by multiple

disciplines throughout the lifecycle of buildings. A range of heterogeneous applications and

versions of applications are used across the disciplines to generate building information models

from feasibility stage through to demolition stage. Several standards have been developed to

support data exchange and integration, however, currently there is not a single building product

data model that successfully represents all of the processes involved in a buildings lifecycle;

Open BIM. This report investigates Industry Foundation Classes (IFC) as a means of data

exchange and integration within Revit and the value proposition BIMserver can provide as an

open source building information model server. The case study presented for investigating data

exchange and integration considers benefits, limitations, quality, productivity and software

technology issues.

Keywords: BIM, interoperability, building data product model, open BIM, standards, IFC, data

exchange and integration, model server.


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1. Introduction

A case study is presented utilising a building information model generated in Revit 2013 to

investigate IFC files as a solution to Revit’s inability to save to previous versions of Revit. It is

common within the AEC-FM industry for numerous stakeholders in a project to have access to

and preferences for different model generation and analysis software applications. Interaction

between the different stakeholder’s model view definitions is required for coordination and

review so interoperability is vital; Open BIM. Currently there is not a single building product

data model that successfully transports a digital representation all of the different activities the

different designers follow from feasibility stage through to demolition (Eastman, C.M., 1999;

Sun M. & Howard R., 2002; http://buildingsmart.com/standards/ifc/model-industry-foundation-

classes-ifc, 2012).

Revit’s SQLite database prevents Revit from saving projects to previous versions of Revit.

However, Revit does support IFC files. The case study model is exported from Revit 2013 as an

IFC file and the IFC file is opened in Revit Architecture 2012. Revit does not import Revit’s own

exported IFC files without loss of data; Revit in combination with IFC results in the loss of data.

This case study investigates the extent of the data lost and modifying the IFC mapping file to

prevent the loss of data on exporting the entities.

BIMserver is utilised as an open source building information model server to manage the

case study IFC files. This report explores BIMserver as a way of generating IFC files and the

value it adds to the management and distribution of the IFC files to multiple stakeholders.

2. Case study

2.1 Introduction to the case study model

The building information model utilised in this case study is an architectural model view

definition of an extension to an existing industrial support building. The model was generated in

Revit 2013. The extension totals 293m2, a ground floor of 187m

2 and a mezzanine level of

106m2. Structurally independent of the existing building, the construction of the extension

consists of Kingspan Insulated Panels fixed to a steel frame. The extension is separated from the


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existing building by a 1hour fire rated Shaftwall partition returned along the adjacent walls for

3m.

Figure 2.1.1 Revit 2013 case study model

2.2 Objective of case study

• Investigate data exchange and integration via IFC, considering benefits, limitations,

quality and software technology issues

• Explore modifying the IFC mapping file to prevent the loss of data on exporting the

entities

• Prove IFC files can provide a solution to Revit’s inability to save to previous versions of

Revit

2.3 Case Study Procedure

1. Export IFC files from the case study Revit 2013 model

3no. IFC file types supported by Revit and based on the IFC 2x3 schema were exported

from Revit 2013; IFC 2x3, IFC Coordination View 2.0 and IFC GSA 2010.

2. Import IFC files

Open the exported IFC file in Revit Architecture 2012 and save as Revit files

3. Review loss of data

4. Modify the IFC mapping file


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2.4 Case study results

1. Export IFC files from model

IFC File Type IFC File Size Revit Architecture 2012

File Size

IFC 2x3 1964 KB 3096 KB

IFC Coordination View 1851 KB 3076 KB

IFC GSA 2010 2022 KB 3104 KB

Table 2.4.1 IFC file sizes

2. Import IFC files

The most commonly used IFC file type, IFC 2x3, encountered the least amount of errors

and warnings.

Figure 2.4.1 IFC 2x3 file, errors and warnings

Figure 2.4.2 IFC coordination view 2.0, errors and warnings


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Figure 2.4.3 IFC GSA 2010, errors and warnings

3. Loss of data

On visual comparison the IFC models appear identical. The level of data lost appears to

be identical in all 3no. IFC files.

Data lost:

• Structural plans and ceiling plans which exist in the default Revit templates (see

figure 2.4.4)

• Site view, section views and schedules created within the Revit model (see figure

2.4.4)

• Topography sub-regions and custom surface patterns assigned to materials within

the Revit model (see figure 2.4.5)

• Gridlines and section markers placed within the Revit model (see figure 2.4.6)


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Figure 2.4.4 Loss of views and schedules


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Revit 2013 Model IFC 2x3 Model

IFC Coordination View 2.0 Model IFC GSA 2010 Model

Figure 2.4.5 Loss of topography sub-regions and surface patterns


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Revit 2013 Model IFC 2x3 Model

IFC Coordination View 2.0 IFC GSA 2010 Model

Figure 2.4.6 Loss of grids and section markers

4. Modify the IFC mapping file


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Figure 2.4.7 Structural columns originally set to IfcColumn in exportlayers-ifc-IAI.txt

file

Figure 2.4.8 Site originally set to IfcSite in exportlayers-ifc-IAI.txt file


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Figure 2.4.9 Ceilings originally set to IfcCovering in exportlayers-ifc-IAI.txt file

Figure 2.4.10 Sections originally set to not export in exportlayers-ifc-IAI.txt file

Figure 2.4.11 Topography originally set to IfcBuildingElementProxy in exportlayers-ifc-

IAI.txt file


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Figure 2.4.12 Wall surface pattern originally set to IfcWall in exportlayers-ifc-IAI.txt file

Figure 2.4.13 Grids originally set to not export in exportlayers-ifc-IAI.txt file

Modifications to the IFC mapping file:

• The structural, site and ceiling categories were originally mapped to the appropriate IFC

classes and yet the structural, site and ceiling plan views are lost on exporting. No

modifications required

• The section category was originally mapped not to export, the IFC mapping file was

modified to IfcBuildingElementProxy

• The topography category was originally mapped to IfcBuildingElementProxy, the IFC

mapping file was modified to IfcSite


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• The wall category including surface pattern was mapped to IfcWall and yet the surface

pattern of the external wall was lost on exporting. No modifications required

• The grids category was originally mapped not to export, the IFC mapping file was

modified to IfcAnnotation

Results of modifications:

On exporting the Revit 2013 case study model as an IFC 2x3 file and opening the IFC

file in Revit Architecture 2012, the section views, topography sub-regions and grids were

lost despite having modified the IFC classes in the IFC mapping file. The loss of data was

identical to the IFC file exported prior to the IFC mapping file modifications.

Figure 2.4.14 IFC 2x3 model (post modifications to IFC mapping file) in Revit

Architecture 2012

2.5 Case study conclusions

Revit 2013 cannot open its own exported IFC files. IFC files exported from Revit 2013 can be

opened in previous versions of Revit; however, data is lost in translation. Productivity and the

quality of the model being exported are affected when data is lost. While all of the geometry is

exported as parametric shapes some of the semantics are lost. In particular semantics associated

with customisations to the standard Revit elements in the default Revit templates are lost. This

suggests that the IFC geometry resource schema facilitates reuse more successfully than the IFC

property resource schema. The International Alliance for Interoperability (IAI) Technical

Committee developed guidelines for developing models, addressing base problems and


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promoting consistency. The guidelines specify that geometry and materials are to be treated as

separate functions:

Recognizing that most objects in buildings have multiple functions, the functions of an

object and its form and material are to be treated separately. An object instance may have

specialised performance properties added to it for uses within an application, but these

properties are not intrinsic (Eastman, C. M., 1999, p.289).

A number of factors preventing the IFC standard from being completed have been documented:

1. The extent of fragmented AEC-FM branch is much more comprehensive than the

extent of fragmented AEC-FM branch is much more comprehensive than the extent

of related industries

2. Unique products

3. Arranged BIM level of detail is not always suitable for all participants

4. Attachment to traditional working methods

5. Growing branch requirements (Pazlar T. & Turk Z., 2008, p363)

Benefits:

• Element categories and sub-categories can be set to not export, the stakeholders in a

project can decide exactly how much of their model view definition to share, as

colleagues on their current project may be competitors for future projects

Limitations:

• Revit cannot import its own exported files without the loss of data

• Elements categories do not have an appropriate IFC class name in all cases, the elements

geometry is exported as a proxy object in the absence of an appropriate IFC class name,

e.g. topography (see figure 2.4.5 and 2.5.1). The sub-regions are lost as a result of the

topography being exported as a proxy object.

Figure 2.5.1


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3. Interoperability

Revit interacts directly with BIMserver via the Revit plugin resulting in an identical level of

data loss as the case study (see section 2.4) as it is essentially exporting the model as an IFC file

and importing the IFC file using Revit’s export and import functions. Until a Revit model can be

exported as an IFC file and the same IFC file can be opened again in Revit without a loss of data

the Revit plugin does not offer BIMserver any additional benefits (http://bimserver.org/2009/05

/25/revit-plugin-to-connect-to-bimserver/, 2012). Building model repositories such as BIMserver

are the future for managing project data but currently some software issues remain (Eastman, C.,

Teicholz, P., Sacks, R., & Liston, K. (2008).

Amor (as cited in Pazlar T. & Turk Z., 2008) wrote about the IFC standard accommodating

the transformation of semantic information between different software applications and each

software application has its own internal semantic representations, therefore perfect semantic

interoperability cannot be achieved. It is possible that we will never achieve perfect semantic

interoperability and we need to achieve an acceptable low level of data loss that will not prevent

smooth collaboration. Other industries have overcome this issue successfully but as Pazlar &

Turk (2008) wrote other industries are not as comprehensive as the AEC-FM industry. In this

industry the range of possible information to be exchanged is vast.

While most other fields whose products are three-dimensional have converted to 3D

modelling and work conventionally using 3D CAD, that transition is just beginning in

architecture. Of all the design fields dealing with 3D products, only the building industry

remains largely 2D and drawing based. The reliance on 2D representations is not because

paper-based representations are better. It is because there are no mechanisms to initiate

changes of such wide impact. In other industries, organisations develop long term

working relations that allow special forms of communication, specifically for exchanging

CAD data. Because the building industry is composed of many small organizations, many

call the construction industry fragmented. This suggests that the organisations best able to

take advantage of CAD may be those vertically integrated, such as design-build

organisations. (Eastman, C. M., 1999, p.29)


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4. BIMserver

BIMserver has many value innovative intelligent functions for the management and

distribution of models that enable higher efficiency and differentiate the users from their

competitors. Managing models and revisions associated with an increasing number of

heterogeneous software applications is becoming increasingly complex and some issues that

arise can be solved by a repository such as BIMserver:

• Supporting exchanges between multiple concurrent applications that both read and write

project data; that is, the workflows are not linear

• Propagating and managing changes that impact multiple application datasets

• When there are multiple authoring applications that must be merged for later use

• Supporting very frequent or realtime coordination between multiple application users

(Eastman C. et al., 2008, p. 88)

IFC 2x3 TCI is currently the only upload option BIMserver provides. Uploaded files are stored

in an object based database for downloading. The system administrator can set a range of other

formats for downloading on an individual project requirement bases.

BIMserver maintains a log of who worked on the model server, what they did and when the

work was carried out. This value innovation affords the stakeholders higher efficiency. Time and

identity stamps are a legal issue (see table 4.1), BIMserver offers a technological benefit

(Somerville J. & Craig N., 2006).

BIMserver utilises a Berkeley database, all of the model entities properties in the database

can be queried. The model browser feature lists a record of all revisions to all of the IFC data.

Improved quality control enables any revision of any model entity to be efficiently located by

any stakeholder. Improved quality control offers the client higher efficiency and differentiation.

BIMserver’s RSS feature, also known as revisions feed automatically updates the main

project virtual revision when a sub-project is revised. Revision feeds are BIMserver’s

notification system for updates and can be checked out. The revision feeds feature saves the

stakeholders time in deciphering if changes have occurred since they last accessed the model

sever. The RSS feature is value innovative and improves the efficiency of the project.

Globally unique ID’s (GUID’s) are utilised by BIMserver’s compare feature. The GUID’s

are compared to produce a list of changes between two IFC file revisions. The differences are

listed by IFC name and GUID and can be downloaded saving the stakeholders time in visually


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comparing two revisions of a model. GUID’s are also utilised by the intelligent merging

function. The compare feature is value innovative, enables the stakeholders to work more

efficiently and offers the client differentiation.

The early warning system monitors workflow collaboration. When a stakeholders checks out

a file as opposed to downloading the model server keeps a log, if a second stakeholder logs into

the model server to upload a new revision they are notified of the active check out. If the

stakeholder proceeds to upload the new revision the first stakeholder is notified the next time

they log into the model server that a new revision was uploaded since their last check out. These

notifications are an innovative quality control measure.


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Benefits of BIMserver Technological

Benefits

Process Benefits Perceived Benefits

Management Issues

Consistency of revisions

Structured data

Reduced handling of documents

Improved administration

Data output

Data import into database

Storage device

Cost savings (note)

Distribution Issues

Speed and transfer of information

Faster response times

Delivery of data

Enhanced processing of

documentation

Distribution costs lower (note) (note)

Legal Issues

Time and identity stamps

Validations of data

Security of process

Safety and reliability

People Issues

Ease of use

Enhanced communication

Interpretation of data

User friendly

Table 4.1 The benefits of BIMserver from technological, process and perceived viewpoint


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Note: A perceived benefit to be measured and calculated for each individual case. Also depends

on current working process (Somerville & Craig, 2006).

5. Current Standards Efforts

A number of standards and efforts have assisted the development of IFC since 1994. The

Technical Research Centre of Finland (VTT), RATAS national building model project, since

1987, and Part 106, the Building Core Construction Model (BCCM), since 1994, in particular

made a significant contribution. The Industry Alliance for Interoperability was started in 1994

and later in 1997 was renamed the International Alliance for Interoperability as Autodesk users

wanted the open neutral IFC standard to be non-proprietary. The IAI drew from the parallel work

of ISO-STEP but in contrast to ISO-STEP the IAI wanted to progress quickly in order to keep

the industry’s interest (Eastman, C.M., 1999). In 2005 the IAI was renamed buildingSMART and

now has regional chapters worldwide. Open BIM is an initiative of buildingSMART and several

software vendors using the IFC standard (http://buildingsmart.com/openbim, 2012).

It has been written that most of the good practices identified in earlier efforts have been

incorporated into the IFC open standard and IFC seems to be a solid response to the need for a

building product data model and the specifications put forward for such a model (Eastman, C.M.,

1999). However, to date IFC requires further development to support a suite of applications

without loss of data. The current IFC version has only partially filled some gaps in the much

needed functionality IFC is lacking. It is yet to be seen if IFC will solve the building industries

data exchange and integration issues.

A step in a positive direction for the industry came in 2011 when the UK Government

announced their intention to require: collaborative 3D BIM (with all project and asset

information, documentation and data being electronic) on its projects by 2016. The BIM Task

Group was put in place bringing together expertise from industry, government, public sector,

institutes and academia. A four year plan was developed to modernise the industry. The groups

aim is to develop more efficient ways for all of the stakeholders in a project to work through all

of the stages in a projects lifecycle collaboratively. Their ambition is to realise this more efficient

way of working through information rich collaborative 3D BIM technologies and processes

(http://www.bim taskgroup.org/, 2012). The AEC-FM industry will be strongly impacted as


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Governments adopt collaborative 3D BIM for use on their projects. The UK Government is not

alone in the attempt to modernise the industry; the General Services Administration and

Singapore have adopted the IFC data model for code checking and design review (Eastman C. et

al., 2008).

Construction Operations Building Information Exchange (COBie) is a working party of the

BIM Task Group and one of the three technical working groups established by Building

SMARTUK. COBie 2.4 is documented for use in the UK (http://www.bimtaskgroup.org/

working-parties/, 2012). COBie is currently being used in the UK as a solution to the

unpredictability and unreliability of IFC. Mapping from COBie to IFC and from IFC is possible

(http://www.bimtaskgroup.org/working-parties/). COBIE is formatted as a subset of IFC, it is a

data schema and can be in the form of a spread sheet or relational database. COBie structures

unstructured data and BIM data as structured single-entry formatted data; this is one of the

advantages COBie has over IFC (http://www.bimtaskgroup.org/building-smart-uk/, 2012). IFC is

considered the long term open source standard solution internationally.

A collection of SQLite databases maintain Revit’s elements, 2013 SQLite databases cannot

transport to previous databases. Revit’s back up files contain databases in tabulated database

format. Revit’s central model is a database, enabling the central model to be opened and adjusted

in Microsoft Access. Local Revit files need to be recreated when a central file is restored from a

backup file as the database has changed. COBIE accesses databases and Revit is a database,

therefore, COBIE is considered more reliable and contractually demanded by the UK

Government.

Tekla Corporation and Solibri Inc. have developed the BIM Collaboration Format (BCF)

schema as another interim solution. This schema is currently pre-release but the intention is for

the schema to inform a software application of issues another software has found in a building

information model. Only the issues will be communicated as opposed to the entire model in the

hopes of improving communication between BIM software applications

(http://www.buildingsmart-tech.org/specifications/bcf-releases/bcf-intro, 2012)


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6. Conclusions and future work

Until the software technology issues within Revit and the IFC data model are resolved and

Revit can be used in combination with IFC without the loss of data, the exchange of data and

data integration will be limited. Depending on the model view definition requirements of the

projects numerous stakeholders, IFC can provide a solution to Revit’s inability to save to

previous versions of Revit. Each stakeholder’s model view definitions geometry is required by

the other stakeholders for review and coordination purposes, IFC can transport geometry. The

general spatial layout of the building is the common thread used in each phase of a buildings

lifecycle (Eastman, C.M. 1999). A BIM integration tool and or automated 3D clash detection

tool may be utilised for coordination purposes but in the event of a previous version of Revit

being utilised by another stakeholder for coordination purposes the data IFC exchanges is

adequate for coordination. The semantics associated with the geometry may not be required by

the other stakeholders in their entirety. The amount of information required by each stakeholder

will need to be accessed on an individual project bases as each application only uses a portion or

subset of the IFC model (Sun M. & Howard R., 2002).

As the construction industry is considered fragmented, the development and automation of

the individual organisations within the industry will benefit the industry as a whole throughout

the lifecycle of buildings. The industry is still largely unprepared for BIM; a portion of the

industry is still designing individually in two dimensions and the portion of the industry working

in teams to design in three dimensions cannot smoothly collaborate. The industry is challenged is

to develop an open source neutral building product data model that can successfully transport a

digital representation of a building project for use by multiple stakeholders in their different

activities throughout a buildings lifecycle. Changes that affect an entire industry inevitably take

time and despite numerous efforts having been made to date there is still not one standard or

model in the AEC-FM industry that can successfully exchange construction data without a loss

of information. The IFC standard may change the current circumstance in the future (Pazlar T. &

Turk Z., 2008). The UK Government believe COBie comes closest to meeting this requirement

at this time. COBie is an area I have highlighted for future study.

BIMserver has many value innovative intelligent functions as a model management and

distribution tool that enables higher efficiency and differentiates the users from their competitors.


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BIMserver adds an extra layer of intelligence to the use of IFC in BIM. Value innovation, higher

efficiency and differentiation have a clear impact on the revenues and profits of a company

(Grilo A., & Jardim-Goncalves R., 2010).

7. References

Eastman, C.M. (1999) Building product models: computer environments supporting design and

construction. United States of America: CRC Press LLC

Eastman, C., Teicholz, P., Sacks, R., & Liston, K. (2008). BIM Handbook. Hoboken, New

Jersey: John Wiley & Sons, Inc.

Grilo A., & Jardim-Goncalves R. (2010) Value proposition on interoperability of BIM and

collaborative working environment. Automation in Construction, 19. 522-530

http://bimserver.org/2009/05/25/revit-plugin-to-connect-to-bimserver/, retrieved November 3

2012

http://www.bimtaskgroup.org/, retrieved December 2 2012

http://www.bimtaskgroup.org/building-smart-uk/, retrieved December 2 2012

http://www.bimtaskgroup.org/working-parties/, retrieved December 2 2012

http://buildingsmart.com/openbim, retrieved December 1 2012

http://buildingsmart.com/standards/ifc/model-industry-foundation-classes-ifc, retrieved

December 1 2012

(http://www.buildingsmart-tech.org/specifications/bcf-releases/bcf-intro, retrieved December 2

2012)


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Pazlar T. & Turk Z. (2008) Interoperability in practice: geometric data exchange using the IFC

standard. ITcon, 13. 362-380

Sommervile J. & Craig, N. (2006) Implementing IT in construction. Oxon, England: Taylor &

Francis

Sun M. & Howard R. (2002). Understanding IT in construction. London, England: Spon Press

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