AECbytes Tips and Tricks Issue #57 (February 23, 2011)

Finding Discrepancies between BIM Models and Contract Documents using Newforma Project Center

Peter Urban
Vice President, Kristine Fallon Associates, Inc.

At Kristine Fallon Associates, we work with a number of contractors on construction phase coordination. Having the architect’s design model is helpful, but poses some challenges. One common concern is the ability to rely on the accuracy of the model in a project where the 2D drawings are the governing documents. This is because after generating the drawing set from the model, it’s not uncommon for architects to add critical annotations or modify a drawing in CAD.

In order for the contractor to take advantage of the architectural model—often provided “as-is,” without any contractual right to rely upon it—they must first perform a thorough review of the model to verify the 3D geometry against the 2D contract documents.

The following process shows how we leverage technology to reconcile the information in the contract documents with that in the architect’s design model.

Getting Started

Let’s assume that you already know how to generate sheet views from the model that represent views in the contract documents. That leaves us with two sets of 2D PDF drawing files:

  • One is from the contract drawings.
  • The other is generated from the architect’s design model.

We make the two drawing sets as identical as possible in regard to scale and alignment, for reasons you’ll see in a moment.

We then use Newforma’s project information management (PIM) software, which includes a digital light table that compares the documents pixel by pixel.

Comparing Drawings

Open a drawing in the Newforma Project Center viewer. This is the contract drawing.

From the Viewer Tasks panel, click Compare to open the Select Revised Drawing dialog box.

Choose the drawing you want to compare to the currently open drawing, then click Open. This is the 2D drawing we generated from the architect’s design model.

If the drawings are not perfectly scaled or aligned, select Modify Comparison from the Compare Tasks panel and align the drawings. Select Align Drawings. Then, select the Scale Drawing or Move Drawing task to align the drawings.

NOTE: The Scale Drawing command scales and optionally aligns the drawings in one step.

From the Compare Tasks panel, click Digital Light Table. The Digital Light Table opens with the two drawings overlaid.

Use the Before-After slider in the Compare Tasks panel to toggle between the two drawings. The “Before” file is the contract drawing. The “After” file is the 2D drawing we generated from the architect’s design model.

The comparison is shown using color coding as follows:

  • Pixels that were not changed in either drawing are dimmed and represented as gray.
  • Pixels that exist in the “Before” file (contract drawing) but do not exist in the ”After” file (model) are colored red.
  • Pixels that exist in the ”After” file (model) but do not exist in the ”Before” file (contract drawing) are colored blue.

NOTE: Color coding only applies if the drawings are nearly identical in scale. We rely on visual inspection, which is made easy by use of the slider, because it creates a sense of motion between one drawing and the other, and humans are adept at seeing movement. Also, the Digital Light Table comparison operates on the current view of the drawings; you can get a more detailed comparison of an area of interest by zooming into the area and then selecting the Digital Light Table task to generate the comparison results for that area.

As we identify discrepancies between files, we can update the model to match the contract drawings.

If you want to save the comparison as an animated GIF file, click Create Animated Comparison. Then enter a name and location in which to save the file. This step is useful on those occasions when we have questions about conflicting information, a process you’ll see in the animated GIF image below.

Encountering Discrepancies

On occasion, we find discrepancies that require more information from the designer or contractor to be resolved. If we find something that we cannot resolve on our own, we issue what we call a “model information request,” or MIR. It’s a request for information that we’ve renamed so as to not be confused with RFIs issued by contractors.

By whatever name you use, requesting information is made easier by functionality that’s already part of Newforma Project Center. The following section shows you how.

Pursuing Model Information Requests

We can take a picture of the model view in two ways; either by using Revit’s Camera tool, or by using the Snapshot function in Newforma Project Center. Because Newforma’s Snapshot function is integrated with other functions, we rely on it to resolve issues. The procedure to use it is described below.

  • In the BIM application, configure the view the way you want to capture it.
  • Right-click the Newforma icon in the Windows Taskbar at the bottom right of the screen.
  • Select Snapshot.
  • Click and drag the box to cover the area of the screen you want to capture.
  • Once you have the box positioned over the area you want to capture, release the mouse button.
  • The snapshot opens in the Newforma Viewer.

Newforma Viewer offers tools to mark up the image. Click the Markup icon at the top of the Newforma Viewer, and select from standard markup tools to annotate the image.

Newforma Project Center provides a tool to manage action items. At the top of the Newforma Viewer, click the Action Item icon. Select the project to which the item belongs.

Fill out the relevant information in the different fields of the Action Item dialog:

  • Enter a subject for the action item in the Subject field.
  • Select the Status, Priority, Disciplines, Due Date, and Keywords as necessary. The Action Item ID is an automatically incremented number that is editable, as long as it remains unique.
  • Assigning an appropriate keyword, such as “Model Information Requests,” makes it easier to track and report the status of similar types of action items.
  • To assign the action item, click Assigned To. This opens the Choose Project Team Members dialog box. Type a contact's email address in the field.
  • Enter a description for the action item in the Description tab.

The file you had open in the Newforma Viewer is automatically attached to the action item. To attach additional files, click the Supporting Documents tab, then click Add to open the Add Supporting Documents dialog box to locate the files. Click Open to add the files.

Click Create to create the action item and add it to the Action Items activity center, from where you can run reports and manage open action items.

If you marked the Send Change Notification Email checkbox in the action item, an email message opens in Microsoft Outlook. Edit the message as necessary. Then, click Send and File in Action Item to send an email message notifying the contacts in the Assigned To, Assigned By, and CC fields, and to file the message in the action item's Email Log.

By sending the model information request via the Newforma Project Center Action Item functionality, you do not have to leave the application to manage the process, and you can return to the Action Items activity center to track and manage unresolved questions.


A typical drawing set includes hundreds of sheets. The procedure outlined above allows us to compare files efficiently and thoroughly without generating paper. It greatly reduces the risk that we fail to spot discrepancies between the design model and the contract documents. Until BIM-generated models function as contract documents, this procedure is a practical way to make the design model more useful to contractors, subcontractors, and the larger project team.


About the Author

Peter Urban is a vice president at Kristine Fallon Associates and a specialist in computer-based solutions for the design and construction industry. He has extensive background in CAD, BIM, and electronic collaboration technologies, and has been a Newforma user since 2005.

Kristine Fallon Associates, Inc. (KFA), founded in 1993, provides IT consulting and services to the design and construction industry. Clients include public agencies, corporate facility groups, design and construction firms, and technology suppliers. KFA’s mission is to deliver complete and effective IT solutions to clients.

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