Visual Estimating: Extending BIM to Construction

In an earlier "Building the Future" article, The Executive Forum and Other Sessions at Technology for Construction 2006, published in January, I commented on the lack of representation from BIM software vendors such as Autodesk, Bentley, and Graphisoft in the Technology for Construction show in general, and specifically in the Exhibit Hall. I found their absence surprising, considering that these vendors were otherwise actively promoting BIM as a revolutionary technology that goes well beyond the design phase to impact construction and lifecycle management as well. While BIM was the topic of some of the sessions at the Technology for Construction conference, there was no sign of it in the Exhibit Hall (see AECbytes Newsletter #26), indicating that while it may be gaining momentum among architects and engineers, it seems to have made scarcely a dent in the construction industry. Most of the technology products at the show for construction tasks such as financial management, project management, document management, bidding, project scheduling, and cost estimation were all built around the paper-based processes of design, communication, collaboration, and construction. Any construction professional attending the show who wanted to find out more about BIM's supposed ability to revolutionize the construction industry would have found little to get excited about.

There is hope, however, that things may be different at the next Technology for Construction conference. Autodesk recently announced its planned acquisition of Constructware, one of the leading Web-based project management and collaboration solutions used by contractors, subcontractors, owners, and program managers. Constructware had attended the previous Technology for Construction show in 2005 (see AECbytes Newsletter #19), where it had reported strong adoption in growth, with $40 billion in projects being managed through its project management solution. While there is some overlap of Constructware's functionality with that of Autodesk's own collaboration solution, Buzzsaw, they have established themselves for the most part in different segments of the industry and can be complementary rather than competitive. Constructware is well established in the construction industry with general contractors and sub-contractors and has demonstrated significant traction in the public sector among government and education organizations, while Buzzsaw's main customer base is in home building, and the retail and hospitality segments of the commercial real estate market. Autodesk's acquisition of Constructware suggests that it is seriously looking to expand into the construction market, and given that it is also one of the leading developers of BIM solutions for architecture and engineering, there is hope that it can make the much-needed push of BIM into construction.

In the meantime, there are also others who are working on extending BIM into construction, and this issue of the "Building the Future" series looks at one such solution, Visual Estimating, developed by a start-up company, Innovaya. It is one of the first BIM-based estimating solutions, which allows a BIM model created in Autodesk Revit (both Revit Building and Revit Structure), Autodesk Architectural Desktop (ADT), or Autodesk Building Systems (ABS) to be cost estimated more accurately and quickly using the leading estimating application in the industry, Sage Timberline Office Estimating. Let's see how it works.

Traditional Estimating Versus BIM-based Estimating

Traditional estimating solutions such as those from Quest Solutions and Vertigraph—just to name two from among those who exhibited at Technology for Construction 2006—use quantity takeoff that relies on manual input of the design into spreadsheets or the digitization of paper drawings using a digitizing tablet. Some of the newer products, such as Takeoff from Quest solutions, allow contractors to generate takeoffs directly from electronic files (i.e., CAD drawings) without the use of a digitizer or physical blueprints. The process involves selecting individual elements in the CAD drawing, and using the software to automatically determine the dimensions for the take-off. It is certainly an improvement over digitizing, but still involves a substantial amount of time to generate the take-off for an entire drawing.

With BIM, the quantity take-off can be greatly speeded up, since the model has the information about all the objects in the building as well as their dimensions. However, it is important to note that it will, by itself, not enable automatic take-off. This is because the estimating process is a lot more complicated than simply getting a list of objects and their sizes. It also involves analyzing the building design, grouping objects into appropriate assemblies for construction, setting assembly and item variables, and then pricing the objects by taking off these assemblies or items. Thus, unless the BIM model was developed such that the objects are derived directly from construction assemblies, the assembly takeoff is still a substantial process in cost estimating. Currently, however, BIM applications do not model construction assembly details, for example, the nails, studs, drywalls, etc. for a wall object. This is why the approach of Graphisoft's Construction solutions, described in AECbytes Newsletter #15, is to allow contractors to create their own construction-specific BIM models rather than re-work the BIM models created by architects and engineers. Innovaya adopts a middle ground here—it works with the BIM models created in Revit, ADT, or ABS by designers, but it also acts as the quantity takeoff and estimating tool which synthesizes the BIM model and enables it to be used directly with construction assemblies and items for estimating.

Innovaya was founded by Dr. Kevin Yu, who was formerly the project lead for Timberline's CAD Integrator estimating solution, which uses the IFC file format to transfer information from an IFC-compliant CAD application into a Timberline estimate. (I actually tested this solution as part of a larger IFC-based interoperability exercise involving multiple applications in one of my Cadence AEC Tech newsletters, which are, unfortunately, no longer available online.) He was also an IAI technical representative, involved in IFC modeling work up to IFC 2.0, and has a Ph.D. from the University of British Columbia in computer integrated construction. He is thus in a good position to develop one of the industry's first BIM-based estimating solutions.

Let's move on to look at how Visual Estimating performs automatic quantify takeoff and estimating for a Revit, ADT, or ABS model using the Sage Timberline Estimating software engine.

How Visual Estimating Works

Visual Estimating works with the API's of the Autodesk BIM applications, and when installed, it adds to them an export option. So in Revit, for instance, it would appear as a command to export the Revit model to "INV," which is the Innovaya file format. Once the Revit model is exported in this format, it can be passed along to the estimator who can open it up in Visual Estimating and carry out the three main steps involved in cost estimating: visualizing and analyzing the design, object quantification, and pricing.

Let's start by looking at its visualization functions. Visual Estimating's user interface includes all the basic navigation capabilities needed for 3D visualization of the imported BIM model. In addition, it allows selective viewing of objects by three basic methods—building sections, component types and individual objects. With each method, the objects' visibility and transparency can be adjusted and they can also be highlighted in the context of the building model. The views can be dynamically determined and selected at any point by the user. For example, in Figure 1, only the structural elements in the model are turned on, allowing the estimator to visualize the structural aspects of the model more easily. Selecting an object provides detailed information about it, such as type, material, dimensions, and so on, all of which comes directly from its description in the BIM model. This interactive 3D user interface allows the estimator to understand and analyze the details of the design model more easily, and is a strategic approach used by the application to move construction users to a true 3D working environment.

The next step in the estimating process is quantification. Since the model encapsulates dimensional information, it has the potential for object quantities to be generated automatically. However, default dimensional data from the BIM model may not always provide the most needed values for the estimator to calculate detailed cost items, depending on how the cost assemblies are configured. In addition to Visual Estimating's selective views which allow the estimator to easily choose the appropriate objects to quantify at a time, it also provides tools to define conditions that specify what quantifies should be calculated and how the objects should be grouped for the calculation of total quantity values. For example, all walls of a specific type that are of the same height can be grouped together automatically and their total length and surface area can be calculated. These conditions can be saved for re-use on the same project or any other projects, allowing automatic generation of quantities for all the objects in the entire building model within a few seconds. Because object quantities are grouped according to appropriate conditions, they can also be organized by classification systems such as CSI or Uniformat codes.

What is also critical is for estimators to be able to see where the quantities are coming from, instead of simply presenting them as a list of numbers without references to their sources. This reduces the chances for missing or excessive quantities, and it provides the estimators with confidence about the accuracy of quantity reports. Visual Estimating's ability to link generated quantities with actual 3D objects and color coding provides this visual confirmation for quantity take-off. An example is shown in Figure 2, where all the different wall types are shown in different colors and are being quantified. Because of the links between the BIM objects and quantities, Visual estimating also incorporates intelligent change management, so that when the design changes and is re-imported, the quantities can be automatically updated. The changes can be color-coded so that they are clear to the estimator. Furthermore, the quantities are also associated with cost items for the subsequent pricing step. The quantity tables that are generated, such as the one shown in Figure 2, can be saved in the form of Microsoft Excel spreadsheets if required.

The final step in the process is pricing/estimating. This is where Visual Estimating's interface with Timberline comes in. The estimator can open up a Timberline database, and drag and drop the quantified objects generated in the previous step into Timberline assemblies or items (see Figure 3), resulting in detailed cost items taken-off into a Timberline estimate file. There is no need for any special configurations and object mappings in order to takeoff the assemblies or items using the BIM quantities. Quantities that have already been placed in the estimate are indicated by a $ sign, and all the cost items in the estimate can be visually confirmed in colors in the 3D view at any point, avoiding over- or under-estimating. As with quantification, since all the objects and quantities are linked with cost items, if the design is changed, the cost items and the estimate can be updated easily.

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The system can also recognize assemblies and items that have been used in the past and record all their variable settings for the particular BIM object types. It allows the entire project to be priced automatically with a single mouse click (see Figure 4), an extremely powerful ability. This automatic estimating feature is based on the knowledge that the system has "learnt" about object types and cost database details from the work done with each project in Visual Estimating, and this knowledge is saved along with the Timberline database. Therefore, it is possible that many projects can be automatically estimated within a very short time without having to compromise the level of cost item details that estimators like to have, such as those provided by Timberline technologies. It is also worth noting that cost databases may contain tremendous valuable information that estimators have defined over years. The power of Visual Estimating is that, without any extra work such as object mappings, these cost databases can be used directly with objects created by BIM applications such as Revit or ADT.

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Analysis and Conclusions

Visual estimating is, as far as I know, the first tool that extends the use of a BIM model created during the design phase into construction. It puts a different perspective on the ongoing debate of "design models versus construction models," and "one model versus multiple models." When the concept of BIM was first introduced, it was with the premise of a "single building model' supporting all aspects of design, construction, and operation. That premise was brought into question as BIM technology was further developed. Graphisoft, for instance, has made a strong case for a separate construction model by arguing that the building model required for construction is substantially different from the model generated during design, and that in most cases, even if a BIM model has been generated by the architect and engineer, it is not very suitable for construction and will have to be substantially reworked—to the extent that it would be easier to simply start from scratch (see AECbytes Newsletter #15). Thus, it has two separate products for creating the design model and the construction model: ArchiCAD to be used by architects; and Constructor, which is built on top of ArchiCAD but which allows contractors to create BIM models incorporating construction information.

In contrast, Visual Estimating does not require a different BIM model to be created by the contractor; it can use the design BIM model created by the architect. And it does this by organizing the information contained in the model such that it can be used for generating accurate cost estimates for construction. Innovaya plans to extent the technology further by developing other construction applications such as scheduling and constructability analysis, doing away with the need to create a separate construction model. As I pointed out in my discussion of Graphisoft's Construction solutions, having separate design and construction models will result in a bigger quagmire further down the road—which of these two models should be used for facilities management, maintenance, and operations? There should ideally be a smart way of deriving a construction model easily from a design model without too much rework, and Innovaya's approach may be one possible solution to this problem.

In terms of adoption by the construction industry, Visual Estimating is promising since it works with the estimators' current workflow and doesn't require them to learn to use a CAD or BIM application. Estimators can visualize the model and create the assemblies they need. They can also work with existing cost databases incorporating the formulas they have used for many years. And in contrast to the traditional drawing-based estimating systems requiring digitization or manual data entry, Visual Estimating is much more efficient and accurate as it totally eliminates the need for measuring, since all the dimensional information is already captured within the model.

Visual Estimating's only limitation at this point is that it works solely with Revit, ADT, and ABS. However, Innovaya does plan to extend this technology to work with the IFC file format, in which case Visual Estimating could work with models created in any IFC-compliant BIM application. It's good to see the rapid evolution of technologies that work with BIM, each of which will play a significant role in delivering on its ultimate vision of "faster, cheaper, and better" buildings. In the case of Visual Estimating, it shows great potential for substantial time savings in the field of cost estimating through the effective application of BIM.

About the Author

Lachmi Khemlani is founder and editor of AECbytes. She has a Ph.D. in Architecture from UC Berkeley, specializing in intelligent building modeling, and consults and writes on AEC technology. She can be reached at lachmi@aecbytes.com.