Frequently Asked Questions (FAQs) to the International User Group

I don't see anything in 3D in my IFC exported from a DWG file

DWG is an Autodesk proprietary format from Autocad, and we will normally not answer questions directly related to export and import to specific formats. However, dwg has almost been a standard exchange format before we started to use IFC so it might be helpful to clarify some of its characteristics.

Traditional DWG-files were in 2D only and they didn’t have objects like in a model, they were just lines, blocks and other drawings symbols. They will not have much relevant information for a model, and it does not seem very relevant to have them as IFC-files. However, they might of course be a good 2D background for modelling work in the authoring tools that read-DWG files, and if you model in Revit or Archicad on an imported DWG background, you may of course export your new model to IFC.

In Autocad Architecture or MEP, you might make building models like in the other modelling tools, and a DWG-file from those Autocad add-ons is in 3D and has object information and you may export to IFC from those tools and it works fine.

However, you cannot expect that other software will read this 3D DWG file with the 3D information. When different software claim that they read and write DWG files, that is normally traditionally 2D DWG-files, not 3D DWG-files. In best case they read the 3D-file as 2D, in worst case you don’t get anything at all. Thus, if you have a 3D DWG-file, you have to do the IFC-export from Autocad Architecture or MEP.

Same GUID (Global Unique Identifier) for more objects

If you have a large project which is split in different models, objects like Site, Building and Storey should actually have the same GUIDs across the different models and the BIM Manager should secure that this is the case. This might lead to problems in software that do not expect this to happen and report error messages.

However, sometimes we have seen GUID duplicates where we don’t want to see that happen. This might be because the model author copy objects instead of establishing new ones and the software doesn’t “understand” that this is a new object. But we have also seen examples where the software establish new objects with already used GUIDS. This, you should bring up to the support of or user groups for your specific software.

Different GUIDS for the same object in different exports

Some software had the bad habit of generating new GUIDs every time a model was exported to IFC. This is of course against the intention of using GUIDs, and is now hopefully not done by any software anymore.

This problem might also occur if the people using the authoring tool delete and make new objects when they should have edited the existing object.

Data loss – some properties disappear when exported

Basically your IFC-export should export all properties, also those which is not standard IFC properties. However, different authoring tools have different mechanisms for choosing which properties that will be included in an export and how the internal properties of your authoring tool are mapped to IFC-properties. Thus, you should bring this up to the support of or user groups for your specific software.

Problems with georeferencing

Sadly, the earth is round and not flat. This leads to lots of problems when you have to make a representation of this round thing on a flat paper like maps or drawings.

There are a number of different coordinate systems in different countries and for different purposes.

IFC4 have the capability to relate to different coordinate system. However, the use is not very well developed, implemented or standardized, and the users need guidance. Thus, there is a work going on in buildingSMART in order to establish an IDM (Information Delivery Manual) for how to do georeferencing the right way and how to implement this in software, so it will be understood correctly both in other BIM tools and in more map-related tools. If you want to learn more about, or take part in this important work, contact the Building room or attend the next buildingSMART Summit.

The objects lose their parametric abilities

Some objects have a complex geometry, so it will never be easy to stretch them in different directions. In IFC2x3, the parametric abilities were very limited and random. In IFC4 they are a little more systematic as a number of object types have a StandardCase-type for the simple types that may be stretched. This applies for the object types beam, column, door, member, opening, plate, slab, wall and window. Those may be stretched, however, the functionality depends upon how this is implemented in the authoring software.

My IFC files are huge

Yes, that might be true. If you have a large BIM model, the IFC files will also be large. Our experience is that the IFC files may be 2-5 times larger than the native format and 5-10 times larger than more compact formats like for example Solibri. The reason is probably that in order to be an open and transparent format, the IFC file is good old ASCII file format. You can actually open the IFC file in your word processor and read it (well, you don’t understand anything, but you have the possibility). Native file-formats are much more efficient, but not open for sharing.

There is also a problem that some software export IFC data by duplicating repetitive information – which in some cases may be faster, but comes at the expense of size. Other applications export IFC data by defining unique data once and referencing it later. This is of course how it should be, and with IFC4 we expect that more software will do it this way.

But does file size  matter? Not really. File size should not be a problem anymore. Networks are fast and disk capacity is cheap. Import and export takes time, but that is in order to convert the model, not reading the file.

What we experience as a real problem, is the software and hardware’s capacity to handle the model. Large models need lots of RAM in your computer and the computer may use long time to generate the geometry. That is not related to the file-size, it is related to the size and complexity of the model and the way the software generates the geometry.  Models with lots of pipes and bends (HVAC and piping) will be much slower than Architect models or models for structure.

In order to avoid problems with your software you should limit the models to cover 10.000 -20.000 m2 of building area if you intend to develop the model all the way to a detailed construction model.

The export is slow

Yes, that has been true. If you have a large BIM model, to export to IFC (and import from IFC) will take time. We have experienced that export of large models may take hours. That will of course depend on the complexity of the model and how different your software’s internal structure is from IFC. We see that some software which have an internal structure more similar to IFC is much more efficient when it comes to IFC export and import than software which have a more different structure.

However, when we see that one software might use 50 times longer time than another to export the same model, there is probably inefficiencies for which software companies have ability to improve.

And we have seen that the latest versions of some of the major authoring software tools has become much more efficient than older versions, so something is happening, and hopefully this is becoming less true.

The good thing is that you don’t need to sit and look upon your computer when it does the export. Start a batch routine in the background or before you leave office in the evening.

What is a roundtrip? Can we do round-tripping with Ifc?

The IFC format is normally used as one-way communication for model authors to export from a native / proprietary format to IFC, either in order to put together coordinated models from different actors or in order to use it as background for design in another discipline or in order to do simulations in a specific tool using IFC. Normally it is not used for further editing.

This is the main use of IFC today, and we see that this works quite well.
IFC also makes it easier to start a new phase with new consultants or to hand over the model to the contractor in a design/build contract. The model may lose some functionality, especially concerning parametrics, but it is a huge step forward from the old situation where the model had to be established once again.

This is the main use of IFC today, and we see that this works quite well.

IFC also makes it easier to start a new phase with new consultants or to hand over the model to the contractor in a design/build contract. The model may lose some functionality, especially concerning parametrics, but it is a huge step forward from the old situation where the model had to be established once again.

A building owner may use IFC as an archive format and then it might be used for editing when the building is going to be renovated or modernized. It will not be as rich as the original authoring format, but it will always be better to have a good model than having nothing in case the authoring software has disappeared in the meantime.

It becomes more difficult if the next party is going to edit the same objects in the model as the originator, and it is even more difficult if that edited model shall be converted back to the originator’s native format for further work.

This is what we call a roundtrip and this is probably the most complex roundtrip. In order to secure that all data is maintained, all the formats have to have the same richness and similar internal structures. If the authoring software have one feature in it’s internal schema that is not covered by the IFC format it will be lost. And similarly, if the editing software have a feature in it’s schema which is not covered by IFC that will also be lost. It is also a problem for software to reconstruct a “foreign” IFC object (at IFC import) with the parametric logic of a native objects. This problem will apply in both directions. Such challenges will probably always be the case as the software developers always will try to add new functionality, that is what they compete about in order to make the software better for us users, and we, the users should appreciate that. It is not in our interest that the development of software ends, as it would if we require full round-tripping of everything from the authoring model.

A less complicated, but also less relevant roundtrip, is to export from one software to IFC and import it back again. However, this will also be a problem if the authoring software is richer than the IFC schema.

A roundtrip the other way, from IFC to an editing software and back to IFC again should be easier to accomplish, as we would expect that IFC always will be the less rich schema. If the editing software are richer than IFC, have all parts of the IFC schema and more, this roundtrip should be possible. This is highly relevant for building owners that want to use IFC as an archive format and will send IFC models to the consultants that is going to design for renovations or modifications of the building.

What do design teams really use IFC for? Does it work? What is just talk and what is reality?

Sharing models within design teams:

Reality. This is becoming quite normal in markets where different disciplines use different software and the BIM-awareness is high. The IFC-model is normally imported in order to be a background from one discipline for the other disciplines design. It is less normal to import the IFC-model in order to edit it with a different software. However, some manufacturers of prefabricated elements, typically steel and concrete, are quite advanced when it comes to use the models from Structure.

Establish aggregated models of all disciplines for design coordination, clash detection, visualization etc.:

Reality. There is a number of third party software for those tasks and they are improving all the time, they are impressive and they are really being used.

Using Ifc for quantity take off, cost estimates, bills of quantities and specifications:

Talk and reality. Using the BIM model for quantity take off is quite normal, both from the native authoring tool and from third party software based on IFC. However, traditions are very different in different countries when it comes to contract formats, who is responsible for cost estimating and who is responsible for bill of quantities for tendering or contracts.

Thus it is difficult to find good and widespread software that is really doing those tasks directly from the IFC model.

Many of the countries where the building owner or his project team traditionally has been responsible for the bills of quantities, also have had national standards for how to present them. In some of those countries you will find quite advanced software that uses the IFC-model to establish cost estimates, bills of quantities and specifications directly from the model.

If you have a 1:1 relation between all building elements that is modelled and the bills of quantities, that will give you a very good control of costs in all phases of a project.

Using Ifc for environmental assessment, energy calculation, carbon footprint:

Mostly talk, but that is not due to IFC. In order to do those tasks we need good informative databases with information about the products environmental data, so-called environmental product declarations (EPD). When we get access to those data this might be more or less the same as doing cost estimates, ie. based on quantity take offs.

Design transfer to contractor or manufacturer.

Many contractors doing digging and excavations for the building pit, use models directly in their machine’s computers in combination with GPS base stations, steering the machines more or less automatically.

Manufacturers of prefabricated elements like structural steel and concrete, are often asking for IFC-models as they often use different software from the design teams, and they are developing very detailed models in order to use them directly in their production lines.

Contractors working on site seems to be slower to adopt the use of models, but this is very different from one contractor to another. You will find all levels of maturity and adoption.

Handover to clients / buildings owners.

For the time being software vendors in the FM market seems to be slow to adopt both BIM and IFC. In the US and UK, a separate standard called COBie has been defined and made national BIM standard. This is more or less a subset of IFC (basically properties without the geometry model) and may be a good start when it comes to delivering model data to FM software. However, there is a need for clear requirements for how to handover the model including both geometry and properties from a project to the operation phase.

Why get involved with a bSI International Users Group Room?

buildingSMART International primary membership structure is the country chapters since they coordinate a countries participation in open standards for BIM, in addition corporations, especially multinational corporations have an interest in advancing open standards for BIM and implementing proven and successful approaches based on those standards. We recognize that there are large sectors of the associated industries that deal with common issues that go beyond country and corporate boundaries. Some of those currently include infrastructure, airports and health care facilities, but more will come as the need dictates.

The benefit to you and your organization in participating a room include:

  • Networking with participants with similar interests about common issues.
  • Identifying international issues common to the subject area so that more members can collaborate on solving the major issues of users, just like you. It simply makes no sense to “go it alone”.
  • Minimizing duplicative work to solve common problems and ensuring your resources are best spent on moving you and the related industry forward.
  • Reducing risk to all members by understanding the full scope of issues and ensuring all aspects of the issue are coordinated and resolved.
  • The primary reason for standards is to gain consensus. When a large group of people agree then software vendors are more willing to invest in developing the tools necessary to implement the strategies identified in the standards, because they are assured a return on their investment.
  • We encourage you to become a member of bSI and of the rooms which will provide the most value to you and your organization.

Contact the buildingSMART management team or the International User Group  chair.

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