Towards open AEC systems

In light of the major API deal recently signed between Nemetschek and Autodesk, Martyn Day explores this new approach to openness at Autodesk and notes that, this time around, things seem a little different

As far as interoperability is concerned, from the get-go, the BIM software sector did not cover itself in glory. If you think about it, that’s bizarre, for an industry which, by its very nature, requires data to flow between fragmented, multidisciplinary project teams.

The problems created by a lack of interoperability were hardly unforeseen. In 1994, the International Alliance for Interoperability (IAI) was set up by Autodesk to define Industry Foundation Classes (IFC) to aid data exchange. But when it came to conforming to IFC standards, even Autodesk itself didn’t do a great job of achieving that goal for decades.

The 2D world eventually coalesced around Autodesk’s DWG, after Autodesk’s competitors all had to reverse-engineer the CAD format. But the move from drawings to new model-centric, proprietary formats like Revit’s RVT set data exchange back ten years – unless, of course, you were all using the same software.

The net result is an industry where applications support various incarnations of IFC, to various degrees of quality, and customers don’t know what they are doing with it. Customers in some countries, such as the US, have just opted for everyone to use one solution from one vendor, and put RVT as a deliverable in their contracts. This, of course, has been great for Autodesk and its shareholders.

As we shift from BIM 1.0 desktop filebased systems to BIM 2.0 cloud-based apps and databases, the whole competitive landscape is set to change once more. The propensity for the industry to keep breaking compatibility is always there, but this time around, something odd is happening. The main vendors are talking about data openness in a way they have never done before, as if it’s central to the next generation of tools.

Given the industry’s history of using proprietary lock-in as a business advantage, this sets off my spider senses. But facts are facts. Bentley Systems has open sourced its next-generation database format iTwin and is available on Github. Market leader Autodesk is also preaching open standards and signing deals with competitors to allow API and APS (Autodesk Platform Services – formerly known as Forge) access. The company has already done technology swaps with PTC, Bentley Systems, Ansys, Cadence and Trimble and is championing and looking to BIM-ify Pixar’s Universal Scene Description (USD) in collaboration with other industry players.

A proprietary world

The truth is the world of CAD goes through cycles of interoperability. Typically, when a software company creates a new desktop design tool, it would develop a file format, or schema, in which to save the customer’s data for loading, archiving or sharing.

Every software company has its own proprietary file formats and each one is unique to the application. Autodesk has .DWG and .RVT; McNeel Rhino has .3dm; Graphisoft has .PLN; and Bentley Systems has .DGN – to name but a few. There is nothing wrong with proprietary or native files, as all applications need to store the data in some structured document type.

With incoherence being built in, the early phases of these new generations of software are the Wild West, as developers duke it out to see who will become the market leader by volume in any market segment; the benefit being that, if you have the most users, then your format becomes a de facto standard. More people will feel the need to buy your software over competing products and that will further drive your format’s dominance, as it’s the most basic, reliable form of interoperability.

The big software battle may move from owning the highest volume ‘branded’ monolithic app or suite to having the most resource-rich, connected design cloud. It will be about where you choose to hold your project information – because customers will bring their connected ecosystems

As total market domination is usually not possible, this leaves competitors with customers demanding the ability to read and write in the de facto format. With some reverse engineering, or by licensing a third-party toolkit, they begin to add support for the market-leading platform. The best historic case in point is Autodesk’s AutoCAD DWG, which dominated the market and still does. DWG is an essential export of any competitive CAD tool.

The problem with convergence on one company’s proprietary format is that all software programmes work differently, have different capabilities and are built according to different concepts. A firm may well have enabled its competitive application to export or import a DWG, but there is a fair degree of internal mapping and conversion of entity types (layers, polylines, linestyles, dim variables and so on) and this is never 100% operable between software with different origins.

After several attempts at including DWG export/import in Bentley Systems MicroStation, but still getting complaints from users wanting enhanced conversion, Bentley took the decision to include all the entity types in AutoCAD in MicroStation, so that data would no longer need to be mapped or translated between the applications. That’s an extreme solution by any measure. The proprietary win in an industry is a very powerful commercial bonus; it means a developer can call the shots and look forward to selling software to supply chains and everywhere its customers touch.

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Reverse engineering

Did Autodesk like the reverse engineering and adoption of others of its file format? Not really. In a story that is too long to tell here, a threat arose with the first AutoCAD clone. A CAD application called Intellicad came along, which used DWG as its core format and mimicked AutoCAD’s capabilities.

Autodesk’s reaction was to mimic Coca-Cola’s response to Pepsi, highlighting that only its own products were 100% DWG. Copycats, it argued, simply could not offer ‘the real thing’.

This led to the creation of the Open Design Alliance (ODA), which pooled Autodesk’s competitors’ reverse engineering knowledge of DWG and provided updated libraries (the ODA went on to develop libraries for DGN, IFC and RVT). It was now increasingly hard to work out where DWGs originated from. Autodesk devised a way to throw a spanner in the works by including a copyrighted phrase in the file. This meant that AutoCAD could be programmed to give a warning when it encountered a non-AutoCADoriginated DWG. Somewhat foolishly, the ODA went ahead and copied this copyrighted phrase and was taken to court, made to pay dearly and had to remove the alert-triggering phrase.

Autodesk’s intention was to warn users that a non-Autodesk DWG could be corrupted, planting a seed of doubt and also helping Autodesk support staff to work out if a problem file was ‘not one of theirs’.

Other CAD firms have gone so far as to encrypt proprietary files, making reverse engineering harder. We encountered this with mechanical CAD (MCAD) software developer PTC when, as an incumbent, it came under extreme pressure from a new upstart called Solidworks. Proprietary formats are a form of leverage, but they contain the full fidelity of the authored data. Pretty much all interoperability standards are lowest common denominator solutions and ‘lossy’.

Over time, DWG became the standard file format in 2D CAD-land, and with every competitor providing support for it, data was able to flow. But then along came BIM and the industry went back to square one, with IFC in its infancy and on a slow trajectory. It wasn’t until 2016, after three years of work, that the ODA released its first RVT libraries. However, Revit changes format with nearly every release, thus always needs reworking.

Developer networks

With customer BIM data held inside proprietary files, developers who want to provide additional solutions to customers and work on that data have needed to become members of the main software firm’s developer networks. For Autodesk, this would be the ADN (Autodesk Developer Network), which allows early access for coming releases, access to APIs and support for desktop products.

With a long-term vision in the cloud, Autodesk introduced Forge in 2015, now called APS (Autodesk Platform Services). APS offers a broad range of services that developers and customers can utilise to create new programmes or incorporate services into their products.

For instance, many developers utilise Autodesk’s Model Derivative API for converting file formats (it supports 70-plus of these). While an application may be 95% written by the developer, they can rely on Autodesk’s cloud capabilities to integrate them with Autodesk BIM 360, Autodesk Construction Cloud (ACC) or to access, open and view a Revit file. Other APS services include the Design Automation API and Reality Capture API, which are paid for by Flex tokens based on use. Pricing can be seen here.

In the past, if one of its developers sold to a competitor, that would result in almost immediate ejection from the ADN, which is understandable, since members get early access to the next release. In fact, Autodesk has historically uninvited longstanding, trusted developers from the Autodesk University (AU) event, for offering a new feature that is deemed competitive with one of its own products.

But again, something different is happening now. Firms such as TestFit (which competes with Autodesk Spacemaker) were uninvited in the past, but are now not only being welcomed back to AU, but also being invited to contribute features to Autodesk Forma, the newish cloud version of Spacemaker.

Snaptrude, which is developing an actual head-on Revit competitor, is allowed to use the Model Derivative service to access RVT and was even permitted to take a booth at AU and run a presentation. One of the conditions of use with APS (5.3 in the terms and conditions), states, “No use by competitors — except with Autodesk’s prior written consent. You may not access or use the Services if you are a competitor of Autodesk”. So they could pull your access to the cloud services unless there is prior negotiation.

Open formats

Despite starting IFC and the IAI, Autodesk’s interest in supporting it went kind of missing in the process. With an American-biased view, I can probably understand this, as in the US, Revit is dominant and IFC is hardly required as RVT is the contractual format.

Prior to the release of the open letter to Autodesk, Autodesk had already been negotiating with the ODA about joining to get access to the IFC libraries, which were now the industry standard. Here, conjecture could be that it was cheaper to license the IFC libraries than develop, or perhaps fidelity was on its mind before the open letter hit.

For the ODA, Autodesk joining was a problem amongst its members. It seems that a special membership status was created to allow Autodesk access to IFC alone, but not the other libraries – for which membership states that firms have to give up all they know about DWG and RVT, which would have been a big ask.

The ODA DWG libraries were also updated by members to support multiple processors and other advances that even Autodesk’s technology didn’t have at the time.

USD is the new format in town and owned and managed by Pixar. Nvidia has based its Omniverse common data environment for AEC users on the format.

Essentially, USD is an accurate mesh, with textures and lighting, and lightweight enough to act as a format to bring in large data models and utilise all the cloud GPU power that Nvidia can provide. Autodesk seems to have fallen a bit in love with the format and has been experimenting with it in manufacturing and AEC.

While Nvidia was scraping data from Revit and hiding it inside its USD, Autodesk wanted to force standardisation, so every developer had the same access. The AOUSD (Alliance for Open USD) was born and joined by firms including Apple, Siemens, Ikea, Sony, Trimble and Hexagon. Extensions are being submitted for inclusion to expand USD applicability to hold metadata for various industries and open for all.

Autodesk and Nemetschek

At the end of April, Autodesk and Nemetschek signed a deal, one that was previously announced rather prematurely by Autodesk at AU in November 2023. Nemetschek and Autodesk have agreed to allow data to flow more easily from each other’s cloud platforms and desktop applications. The interoperability is made possible by connecting Nemetschek’s dTwin, Bluebeam Cloud, BIMcloud and BIMplus industry clouds to Autodesk’s industry clouds—Forma, Fusion, and Flow—as well as design solutions through Autodesk Platform Services (APS). This will enable customers and partners of both firms to connect their data and capabilities across the mixed solutions.

Under the terms of the agreement, the Nemetschek Group and Autodesk will provide mutual access to their APIs and industry clouds, thereby giving developer access to Nemetschek solutions including Allplan, Archicad, Bluebeam, Maxon One and Vectorworks, as well as Nemetschek’s relevant cloud platforms, and similarly to Autodesk solutions including AutoCAD, Revit, 3ds Max and Maya, as well as Autodesk Forma and Autodesk Construction Cloud (ACC). This will enable the two companies to improve upon existing data exchanges and open new data-centric multi-disciplinary workflows.

The deal seems very broad, but is also very specific to a range of tools on both sides. The fact that it took so long to negotiate suggests there was a lot of quid pro quo to ensure both parties felt they were getting enough in return for opening access. These are, after all, the number one and two vendors in AEC. Nemetschek has three BIM modellers (Archicad, Vectorworks and Allplan), to Autodesk’s one (Revit). It leads me to wonder whether, if Nemetschek acquired a developer, would it have to add that to this list by negotiation, or is the APS access open to all Nemetschek brands?

So what does this all mean? Autodesk is undoubtedly evolving an open strategy in its AEC market play. I am sure that Autodesk will allocate this to listening to its users, but US firms are just not asking for open systems, as they are in the RVT ecosystem. It’s Europe and the rest of the world at stake here, perhaps, but I feel that the fundamental driver to this open view lies in the destination for the next design platforms: the cloud.

It might not seem like it right now, but the file-based world will eventually give way to interconnected design clouds from vendors, loaded with customer databases of projects. These will need to be granular, portable or accessible, since customers will demand it. The big software battle may move from owning the highest volume ‘branded’ monolithic app or suite to having the most resourcerich, connected design cloud. It will be about where you choose to hold your project information – because customers will bring their connected ecosystems.

The ‘trap’ may be that, by hosting all project data in Autodesk’s new unified database (which is proprietary), there will be big benefits through AI and automation, with layers and layers of geo-referenced information available for analysis. The only way to ‘get your data out’ of this database would be to slice up the database, reverting content back into its constituent native files, which by then, will feel like a move as regressive as going back to DXF.


If you are interested in openness and its future in the AEC industry, please join us at our NXT BLD and NXT DEV conferences at London’s Queen Elizabeth II Centre on 25 / 26 June 2024.

You will have the opportunity to learn about new initiatives and take part in discussions on what the industry wants moving forward.

Industry Foundation Classes (IFC)Industry Foundation Classes

Industry Foundation Classes (IFC), originally created by Autodesk but now managed by BuildingSmart, is closely aligned with the STEP exchange format and now has extensive support for architectural and construction entities (walls, doors, windows and so on).

There are three commonly supported variants; IFC: IFC2X3 (ISO standard since 2006); IFC4; and IFC4x3; with 4×4 in development. Since 2020, major work has been put into the restructuring of the core of IFC for IFC 5, in order to expand to accommodate smart buildings, smart cities, digital twins, granular level access, cloud streaming and many other capabilities.

Universal Scene Description (USD)Universal Scene Description

Universal Scene Description (USD) was originally developed and open-sourced by Pixar Animation Studios to help its multidisciplinary teams share complete 3D ‘scene descriptions’ between a mixture of different software applications. It supports a variety of elements such as mesh geometry, materials and animations.

While it currently doesn’t officially support any embedded BIM data, the Alliance for Open USD (AOUSD), headed up by Nvidia and Autodesk seeks to expand the format to better accommodate the data needs of the industry ( USD is owned by Pixar but the plan is to make it an ISO standard.

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