In a surprise announcement from Prague, the Open Design Alliance said it has been working for three years documenting the two primary file formats used by Autodesk Revit: RVT for native model files, and RFA for family files used by symbols. ODA president Neil Peterson says the alliance will release an initial API [application programming interface] on January 1, 2107 to its members, named Teigha BIM. (See figure 1.)
Figure 1 ODA president Neil Peterson presenting at the annual Open Design Alliance Conference 2016 in Prague (Image credits Ralph Grabowski)
Before then, however, the ODA is already shipping a set of libraries that read everything in RVT and RFA files. Members who want to import Revit data are already doing this now, such as Vectorworks and Bricsys. To do so, they ponied up $30,000 to cover the development expense; other members are waiting for January's release to pay lower fees of $5,000 - $10,000 (per year, royalty-free), depending on the level of access they need to the API.
To understand the complexity of the task the ODA undertook in documenting the entire file format, it turns out that Revit has 3,800 classes, of which 2,700 have data. (The other 1,100 contain no data.) All data for all entities are accessible through the ODA's TfObject interface, but this is a low-level interface. Being low-level, it is, however, inconvenient to use, and so the ODA is working on high-level custom classes. So far, they have written access to 1,600 of the 2,700 data-containing classes. These 1,600, the ODA says, contain the most commonly used classes found in real-world drawing files. (See figure 2.)
Figure 2 Teigha BIM viewer displaying 2D drawings and 3D models from Revit
The API provides the following benefits, the ODA says:
Access data in Revit files without needing a license of Revit. Three years of an annual Revit subscription is $6,000. (Autodesk currently costs its annual subscriptions at 1/3 of the software's former permanent license price.)
Read 2011 through 2017 formats, and write back to 2017 format. (For saving, older files must first be converted to 2017 format.)
Full and partial loads of RFA and RVT files. (The Teigha Kernel is used to parse the database.)
Display ("render") 3D Revit geometry. (For 2D data ODA uses its own format)
Currently handles Revit's 2D and 3D primitives: line, arc, ellipse, hermite spine, NURB spine, and cylindrical helix; polycurve and polymesh; plane, cone surface, cylinder surface, revolved surface, ruled surface, hermite surface, and shared surface; b-reps. Also displays connectors (see figure 3), dimensions, rectangular clipping, and so on.
The official release in January includes production rendering support, a more complete set of high-level entity classes, and the ability to create a small set of Revit entities and then save them to file.
Figure 3 Teigha BIM viewer displaying a connector from Revit
To write all Revit entity types fully to file will take an estimated five years. "Entity creation is the most complex part of the work," says ODA president Neil Peterson. No IFCs are used; IFCs [industry foundation classes] are a vendor-neutral way to exchange data between BIM programs, kind of like IGES and STEP are used by mechanical CAD.
Architosh editor Anthony Frausto-Robledo describes what Teigha BIM encompasses: "Teigha BIM provides direct access to database objects (managers, tables, curves, brep, et cetera) as well as families [symbols] and BIM objects like doors, windows, slabs, roof, HVAC elements and more all in .rfa and .rvt files."
CAD journalist Randall Newton explains the need for an API like Teigha BIM: "Independent support of the Revit file formats is not just about independence from Autodesk. A Web site that wants to display Revit models, but does not run a Windows-based site (most of the Web), has until now no way to render and display the models. The Teigha BIM Kernel solves this problem"
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The WorldCAD Access blog was the first to announce this new development, perhaps the most significant since the ODA made direct DWG access respectable. Here are links to some of the initial coverage of the new Revit-independent API:
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Industry Reacts to ODA's Teigha BIM API
To determine the impact that Teigha BIM will have on the industry, I asked a dozen CAD companies for their reaction to the technology, some of whom responded in time for my deadline. I list them below in the order in which they replied.
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Vectorworks: Already Implemented
Vectorworks has integrated Teigha BIM 1.0 libraries into Vectorworks 2017. The import API is behind the implementation of our new Revit Import command in Vectorworks 2017. The command can import both .rvt and .rf files. - Dr. Biplab Sarkar, CEO Vectorworks, USA http://www.vectorworks.net/2017
IMSI/Design: Thinking About It
We are interested in adding this functionality to TurboCAD. We think that it fits with our "simple BIM" additions we've made the last few years, such as IFC support. It is our position to provide robust file interoperability in the Pro and Pro Platinum versions of TurboCAD.
That said, we need to look at the dollars and cents of the additional licensing cost. The standard cost for this Teigha library looks like it is going to be $10,000 per year. But due to the wider interest in BIM as compared to other ODA SIG projects -- like Civil and Mechanical -- there will be two other licensing levels introduced in January. I don’t believe the ODA has finalized these yet, however I think it is more likely we would go with one of these. - Bob Mayer, President IMSI/Design, USA http://www.turbocad.com
Bricsys: Working On It
Within the ODA, we are an active member of the Teiga BIM SIG [special interest group]. Bricsys has been developing new BIM software that is 100% .dwg-compatible using the latest 3D direct modeling techniques for maximum intuitiveness.
A first requirement is to be IFC-compliant. We are days -- maybe a few weeks -- away from being certified. We are convinced that the IFC format becomes an important collaboration enabler. It's a kind of like insurance that ensures you can exchange geometry and data to a certain degree. But ideally you want to retain the dynamic behavior of objects when importing and exporting them.
We have no plan -- nor any other company, I guess -- to build software similar to Revit. Teiga BIM is delivering for us and others an opportunity to communicate more directly with Revit object families (RFA files) and Revit models (RVT files). Compare this approach with our Communicator module, which is based on ACIS translators: it is a tool to translate objects from other file formats in the most meaningful way and with much intelligence retained while importing and exporting back and forth.
In a world of global collaboration it should be unthinkable that any given file format lacks intelligent exchange capabilities. It is common practice in the 3D mechanical engineering software industry, and there is no reason I can think of why the AEC space should be different.
Bricsys is already working with Teigha BIM. The challenging goal we aim for is to import Revit's parametric objects (windows, doors, furniture, and so on) stored as .rfa Revit Families files, and converting them to BricsCAD BIM parametric components. (These are our 3D versions of "dynamic blocks" containing DWG solids controlled by parameters and 3D constraints.) Our goal is to make this translation possible without the need for manual interaction.
This is work-in-progress, as today we can import .rfa geometry composed of extrusions, and can translate some meaningful parameters and constraints. Over time we intend to import data along with geometry, and to cover more geometric primitives, such as revolutions and sweeps. Teigha BIM provides the necessary read-access to both geometry and data.
Revit itself exports parametric objects to DWG and IFC files, but only as static geometry. Such a workflow does not allow translation of constraints and parameters, and prevents us from creating living BricsCAD BIM parametric components. Therefore, we need to implement our own RFA import based on Teigha BIM.
A recent Building Smart meeting described -- among other things -- making parametric data exchangeable using IFCs. Assuming that Revit will want to be certified for IFC 4.0, it seems like this will be a second route to the same intelligent exchange as what we want to use Teiga BIM for. - Erik de Keyser, CEO Bricsys, Belgium http://www.bricsys.com
The editor replies: The ODA reports that is not currently working with BuildingSmart, does not feel that IFC 4 is a competitor to Teigha BIM, might consider IFC support in the future, and right now is concentrating on core Revit drawing access.
Mr de Keyser responds: There is a difference in approaches between IFC and Teigha BIM:
Building Smart defines the rules -- such as IFC 4 -- for software to communicate. This means that Autodesk has to extend Revit so that it is compliant with IFC rules; other BIM software vendors, such as us, will do the same. Once both BIM packages implement IFC 4, then they can talk more intelligently to each other than under IFC 2.x, say.
ODA delivers source code and binaries so that its members can modify their code to also talk to Revit. As of today, Revit is not IFC 4-compliant. This level of communication differs, depending on a lot of elements. I expect that we can go much further with Teiga BIM, because we can decide for ourselves how far (and when) we go [to access Revit data independently of Autodesk and BuildingSmart].
Without Teiga BIM, we all depend on the willingness of Autodesk to do the job. IFC 4 becomes the limit to exchange.
To properly evaluate the software offering (and available libraries) will take longer than one week for sure. Teigha BIM would be convenient, although our users are fairly accustomed to exporting information via IFC anyway. But should it work well, Teigha BIM would save us writing a Revit plug-in ourselves. From a business perspective, it would reduce the cost, assuming it works as advertised. On the other hand, it might be difficult for the ODA to keep up with Autodesk releasing incompatible versions every year. For instance, we came across a case where one of our architectural clients is using Revit 2013 only to be told by Autodesk to upgrade to 2016, as 2013 was no longer supported. After the usual file upgrades, all balustrades disappeared! -Dr Jozef Dobos, CEO 3D Repo, United Kingdom http://3drepo.org
The editor replies: The ODA has found that Autodesk updates Revit as often as twice a year. They plan to support Revit back to version 2011.
Stabiplan: No Need
Interoperability is at the heart of BIM. Stabiplan, being active in the Autodesk ecosystem, primarily focuses on delivering high end software for MEP [mechanical, engineering, plumbing] design on Revit and AutoCAD.
However, collaboration requires support for other formats as well. That's why Autodesk and their partners support interoperability based on IFC. I can imagine Teigha BIM can have an effect on the MEP industry in the future. But as the MEP industry is highly dominated by the Autodesk products, today we see no urgent need from our customers to access Revit files without having a Revit license. - Edwin Schalk, Business Development Director Stabiplan, The Netherlands http://www.stabiplan.com
Graebert Gmbh: Thinking About It
The role of the ODA has been paramount in establishing a robust alternative for DWG and DGN compatibility. We believe that the new Teigha BIM libraries will just as significantly impact the market and contribute to strengthen innovation in our industry.
Graebert's primary interest will be for its SiteMaster range, which is specialized for building surveys. Our solution SiteMaster BIM is used to acquire the 3D geometry of buildings in a more efficient and cost-effective way than 3D scanners. As SiteMaster BIM currently exports to IFC and models are frequently (but not only) used after with Revit, it will make sense to develop an exporter to the Revit file format.
Autodesk is a long-time supporter of openness demonstrated by our interoperability agreements with Trimble and Bentley Systems, and alliance with buildingSMART International. We understand that our customers use a mix of products in their workflow and providing them with the flexibility they need to get their jobs done is our top priority.
Autodesk is making Revit data more available and accessible to our customer ecosystem. We’re committed to maintaining our best-in-class IFC support, and providing more open access to Revit data through Forge services like the Model Derivative API. However, we believe it is in the best interest of our users to provide access to Revit model data through ways that preserve the integrity and accuracy of that data -- and accordingly encourage the use of applications developed with Revit’s API.
NX 11 from Siemens mixes facets, surfaces, and solids with its new Convergent Modeling. (See figure 4.) In most other CAD systems, you have to convert one format to another before working with two or three of the modes, but not in NX 11. Facets come typically from 3D scans, and tend to be incompatible with solids modeling.
Figure 4 Solid modeling mixed with facets from a 3D scan
Siemens describes it like this: "[3D scans for] reverse engineering of existing designs has traditionally been an expensive and tedious process, because the scanned data requires a time-consuming manual conversion of the faceted geometry into surface and solid form before it can be used for further modeling. Convergent Modeling greatly reduces the need for this rework by bringing the scanned data in as facets that can be worked directly in NX 11, so there is no need to map surfaces, create solids, or do any other manual shape creation."
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