Thousands of Clashes in a Thousand Seconds

Every BIM coordination will inevitably use different file types and have varying degrees of complexity for each trade. Often, clash tests between individual trades will produce thousands of clashes per floor that make a manager’s task of organizing them seem daunting.

Autodesk® Navisworks® 2013 has added a few goodies to make coordinators’ lives easier and allow them to manage thousands of clashes with fewer headaches.

A Little Housekeeping

Wouldn’t it be great if we could reduce the amount of clashes before even opening Navisworks? Well, with some trades, exporting DWG files through Autodesk® Revit® can reduce clashes. Most trades ask for DWG files to Xref while they model. The trades modeling in Revit will export DWG files as a batch export with all their levels cut up, instead of having to export 30 different NWC files one view at a time. I know this article is about Navisworks and we’ll get to that, but if you ever run into this issue you will be grateful you know a little Revit.

The default settings in Revit will export DWG files as polymesh solids, which separates all the solids into surfaces. This may not be terrible for use in AutoCAD®, but it will wreak havoc on a clash test—tripling the amount of clashes, or worse.

In Revit, if you click on the ellipsis in the DWG export screen you will get a window with some tabs. Under the “Solids” tab you will have two options—check the “ACIS solids” box instead of the “Polymesh” box.

Figure 1: Same systems exported with one difference.

Figure 1 shows that a small setting will drastically change the number of clashes between two trades. I realize that anyone exporting NWC files will not have this issue, but those who run into don’t have to worry.

Thousands of Clashes

So what do you do when a project has thousands of clashes between individual trades on individual levels no matter what you try? And what if those thousands of clashes break down to hundreds of real issues? How can you quickly prepare your model for a coordination meeting and still have the confidence that you haven’t missed any or created duplicates? Grouping clashes together is one of Navisworks’ greatest strengths. There have been many articles devoted to grouping clashes, so I will not focus that much on the basics of grouping, but rather the workflow of handling thousands of clashes that has become easier, thanks to Autodesk.

Quick disclaimer: Everyone has their preferred methods of managing clashes. I am not here to tell you this is exactly how you should manage your clashes. Rather, I am simply offering my advice on how it can be done efficiently and accurately.

So after you have created and organized all your search sets and clash tests, and have created custom rules to eliminate as many false positives as possible, you are ready to jump head first into the ocean of clashes. The first thing I recommend doing is turning that ocean into a lake by grouping ALL your clashes into one group. You can do this by highlighting all clashes and selecting the group button located just above your clashes window (see Figure 2).

Figure 2

With a few thousand clashes, this process may take a few minutes per clash test. Be patient with Navisworks and remember that just because it seems to have crashed doesn’t mean it really has. Navisworks enjoys working with thousands of clashes about as much as you do. If I had one wish it would be to have the option of Navisworks automatically grouping all new clashes—this would save a lot of waiting time. Maybe in 2014...

Now that all your clashes have been grouped, your patience will pay off. With your new group selected, the “Hide Other” isolation option will give you a holistic view of the issues. Whether you choose to focus on small clashes or just large constructability issues, this group will be your Main group.

Now I know some of you will say that you can get a holistic view just as easily by using the “Dim Other” and “Transparent dimming” without having to wait five minutes for Navisworks to make your group. This may be true, but try walking around a complex model with transparent dimming versus a hidden one. Your computers will thank you, and through this “Hide Other” workflow you won’t be missing any issues or creating duplicates.

With the “Hide Other” on, you can begin to walk through your model looking for issues. Once you find your first issue you can use the Select Box to highlight all the pieces of geometry related to that issue, (Shift + Select Box will select anything touching your box). The Filter by Selection tool has always been useful, but in Navisworks 2013, Autodesk has made a wonderful change to it. Now you can select filter clashes that are INSIDE a group! In 2012 you would have to explode the group for select filter to work, but not anymore.

After selecting your clashing geometry and turning on “Selection Filter,” you will see all the clashes disappear except for the ones relating to your selection. If you highlight those clashes you can remove them from group or make them into their own group—either way you want to remove them from the “main” group.

Figure 3: The clashes separated from our main group no longer clutter our view.

Once the clashes pertaining to our first issue are out of the main group, you will turn off “Select Filter” and select the Main group again with “Hide Other” on. You will now notice that you can’t see the issue you just focused on because it is no longer in your main group, but that’s great because you don’t want to see the same issue again—you’ve already marked it. With the first issue separate, you can move on to the next issue and never have to worry about duplicate clashes popping up in your coordination meetings.

The process is simple; we are taking our ocean of clashes and localizing it into a lake of clashes that we can view without dimmed objects slowing down our computers. Then we are taking individual pools of clashes and separating them out until we are left with the sludge of false positives that we can then discard.


Now we have all our clashes organized and we are ready for our coordination meeting. Because we have each issue separated, we can quickly move from issue to issue during the meeting, redlining and tagging along the way.
Because we have grouped our issues separately, when we write a report we can select “Group Headers Only.” This is telling Navisworks that we only want to see the grouped folders as viewpoints and not the thousands of clashes we have inside those folders. With the service packs installed, Navisworks will bring over redlines and tags into those new viewpoints.

Figure 4: Writing a report as viewpoints.

Navisworks 2013 has given us a new feature with reporting, but you have to be careful when using it. You have always been able to create a report using viewpoints, but those viewpoints would be saved without any “Hide/Required” attributes. Not anymore. Autodesk has made us a little more dangerous—now when you write a report you need to be very careful about your “Isolation” settings. Any isolation you have selected as well as any section cuts you have turned on will be applied to all the new viewpoints you write using reports.

After the viewpoints have been made, you get a folder with the clash test name and inside it a “Reset Appearance” view and then a folder with the grouped clashes. When you select the folder it will go to whatever view you had saved for your group in the clash detective and it will have any isolation settings you had.

Figure 5: Viewpoints written as a report save their visibility attributes.

We write reports as viewpoints because they can be viewed in Navisworks Freedom. Being free, we expect all our trades to use it so they can go over everything that was covered in our coordination meetings and hopefully have those issues resolved in time for the next meeting.

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