clash detection

Revit Technology Conference Singapore – September 10 – 12

Come and see me speak at the Revit Technology Conference in Singapore from September 10-12 at the Equarius Hotel on Sentosa Island!

I will be presenting two talks, one on Navisworks clash detection and another on documenting MEP models in Revit, as the Singapore BIM mandate keeps marching forward toward the next goal of an FM mandate it’s important to get a handle on tools of the trade and how to make them work for you.

You can register to attend the event on the RTC website here.

Navisworks Quick Tips

I’ve been focusing a lot on documenting Navisworks procedures at work of late, for whatever reason Navisworks seems to be seen as some black magic witchcraft software package that no one wants to admit that they don’t entirely understand how to drive.

I sat in on a Navisworks session at the Revit Technology Conference last week just to see what others were up to and there was a surprisingly large turn out. The content presented was very much in line with my previous Navisworks articles and quite a few attendees seemed to be new to how

Helpful Tips

So based on that, I have two quick tips for Navisworks users, the first is selecting elements with a mouse click. When selecting elements in Navisworks, you might be selecting faces of elements or even the entire file rather than the whole element.

You can change what you select when clicking by heading to the Home tab on the ribbon and then heading to the Select & Search panel. Click on Select & Search and you will now see a drop down box.


You can then choose what you want to select with your mouse clicks. If you want to select individual elements, you will want to choose First Object.



The second tip is about the data that you export to Navisworks from Revit. You may remember in my Navisworks 101 series that I spoke about improving your clash detection with selection sets. To create really powerful selection sets, you need the data to drive them but you need to make sure that you’re exporting that data in the first place.

To correctly export Revit parameters to Navisworks you need to make sure you have the option Convert element properties checked – by default this setting is turned off.

You can find this option in two places. The first is Navisworks itself. Head to the application menu and select options.


In the options dialogue box, in the left hand sidebar find File Reader and then select  Revit from the list, then from the options in the right hand window, check Convert element properties.


You can also find this setting in the Navisworks exporter addin within Revit itself. Simply head to the Addins tab on the ribbon, then from the External Tools list choose Navisworks 201xright_circular-32Navisworks Settings and then check Convert element properties

The difference between the information you get in Navisworks when you change this setting is chalk and cheese.

With the setting unchecked


With the setting checked


As you can see, checking this setting will export additional parameters and properties related to the element including material information, associated level, shared parameters and much more.

Having this information available within Navisworks will allow for more accurate selection sets to allow for better clash detection results as well as time lining and quantities.

Navisworks Clash Detection 101 – Part #3

Part #3 – Understanding Clash Types and Tolerances

One of the most misunderstood parts of Navisworks clash detection is the settings for the clash type and the tolerances. Using the model from my hydraulic pipe sizing article I have put together an example of the different clash detection types at varying tolerances. I’ve added some columns to the model which are progressively offset at 25mm intervals. You can clearly see that there are columns that clash, and columns that do not clash with the drainage pipework.



I’ve then created two selection sets as explained in the 2nd part of my clash detection series, one for columns and one for the drainage pipework. I have then created a series of clash detection rules that clash the columns selection set against the sanitary drainage selection set, the clash reports repeat at different intervals.


For the hard and hard conservative clash reports, I have selected tolerances of 10, 20 and 50mm and for the clearance clash report, I have selected tolerances of 20, 50 and 100mm. When running the clash reports, I get the following results:


As you can see, as you increase the hard clash tolerance, the clashes reduce and as you increase the clearance tolerance, the clashes increase.

Hard clashes are as the name implies – a hard clash but as you adjust the tolerance, the clash is ignored within that tolerance range. Allowing for a 50mm hard tolerance means that two items need to intersect or clash by 51mm or more before they are reported on. The clash shown below has been reported in our 10 and 20mm tolerance reports, but completely ignored in our 50mm report.

There is no denying that this is a clash, yet it’s not reported in the 50mm tolerance test at all.


Clearance clashes are the exact opposite of a hard clash. Clearance clash reports check elements for minimum clearance requirements. In a clearance clash test with a 50mm tolerance, two elements will need to be 50mm apart or closer to be reported as a clash. This is particularly useful when you want to allow additional clearance for pipe, cabletray or duct hangers and brackets that have not been modelled.

As you can see in the reported clash below, the two elements do not intersect at all, yet they are still reported as a clash due to the minimum clearance not being met.


But What if my Elements are smaller than my tolerance?

That’s actually an interesting question and can prove useful or troublesome in clash detection reports. I’ve added a 20mm gas pipe to my example model which in plan intersects with my 15mm cold water droppers that run to each basin. Again, you can clearly see that the newly added gas pipework clashes with the existing cold water pipework.


I’ve in turn created a series of clash tests, this time I have only created hard clash tests with tolerances of 0, 10, 20 and 50mm.


The reports give interesting results. Only the report with a 0mm tolerance has reported any clashes at all. Results like these have the chance to run you into trouble if the clashes can not be resolved on site – say for example a 65mm vent pipe rising inside a 90mm stud wall and a 32mm chilled water pipe running horizontally in the wall cavity; there is no way the two services will ever fit and yet they’re not reported in Navisworks.

These settings though can also be used to your advantage. For example if you have modelled all the hot and cold water pipework to the individual fixtures, you would never be expected to coordinate pipework of that size and how can you when the architect doesn’t model the studs within the walls? Using the tolerances to your advantage you can avoid having essentially false positive clashes reported.

Navisworks Clash Detection 101 – Part #2

Part #2 – Sets

Sets are a big part of clash detection in Navisworks, they can make the difference between a great clash report and one that is a waste of time. Simply clashing one model against another is not going to give you great results in most instances. Say for example you clash an architectural model against an electrical model, that’s all you need to do right? Wrong. Every electrical item that is recessed into either the wall or ceiling will be reported as a clash which this actually isn’t a clash, you end up with a time consuming administration overhead to manually approve clashes that shouldn’t have been reported on in the first place. This post will help you get your head around sets and how to make them work for you.

Selection sets are a group of objects selected either from the view window or from the selection tree window. You can manage sets from the sets window, if your sets window isn’t visible on screen, head to the View tab, and from the Windows button, select Set from the list.


The Sets window allows you to manage your search and selection sets within Navisworks.

Below is a description of each of the buttons in the Sets window.

1 Save Selection is used to save the current selection.
2 Save Search is used to save the current search.
3 New Folder allows you to create a new folder to group sets under.
4 Duplicate is used to create a copy of the saved items.
The Add Comment is used to add comments to the saved sets.
6 Delete is used to delet the selected set.
The Sort button is used to arrange the saved sets in alphabetical order.
8 The Import/Export button is used to import and export the saved sets.

When you run a search in the find items window, the search results will be highlighted in blue in the view window, as well as in the selection tree window.

When you select an object or a group of objects, they will be displayed in the Selection Inspector window along with their properties.


2015-03-02_13-25-54 The Show Item button is used to view the selected object in the display window. The display will zoom in on the selected items when you click this button.
2015-03-02_13-26-01 The Deselect button is used to remove objects from the selection inspector window.
2015-03-02_13-26-40 The Export button will export the selected item to a *.CSV file.
2015-03-02_13-34-37 Save Selection allows you to save the selected objects as a selection set.
2015-03-02_13-35-18 Quick Properties Definitions allows you to add properties to the selected objects in the view window.

Now that I have explained the functions of each of the window elements, I’ll show you how to put them to use.

Using the Find Items window, you can search for elements based on specific information. In this instance, I have searched for all air terminals located on level 1. The find items window will allow you to search for elements based on the element properties which includes user parameters.

Once I have the correct elements selected based on my search, I can create a selection set in the Selection Inspector.
I now have a selection set named Level 3 – Air Terminals in my Navisworks model.

Following the same method, I have created a selection set of all the lights on level 3. In the next installment, I’ll explain tolerances and how they affect your clash results.

Navisworks Clash Detection 101 – Part #1

Part #1 – The Clash Detective Window

To the average engineer or modeller, Navisworks and clash detection go hand in hand, some people think that they are one and the same. If you’re not familiar with the terminology, clash detection is a process that identifies interference between elements in your model where as Navisworks is an Autodesk product that facilitates automated detection of the interferences between modelled elements. These interferences, or clashes may be between different models or within the same model, they could be between disciplines or within the same discipline.

The concept behind clash detection during the design process is that you can identify and fix problems before construction begins, therefore saving time and money down the track. Provided that it is configured correctly, Navisworks can help to speed up the process and reduce human error during model inspection by running automated clash reports.

The problem with Navisworks however is not everyone knows how to use it effectively. Maybe you’ve been to training with a reseller in the past and you walked out the door still scratching your head. After spending a whole day working on 4D timelining, 3 hours showing you how to animate an automatic door in Simulate and less than an hour spent learning the very basics of clash detection in Manage or maybe you’ve had no training at all? Either way you’re only just barely making your way through your clash detection sessions.

Over my next few articles I will outline a few of the clash detection basics to get you more confident in your adventures into clash detection, I’m not going to claim to solve all your clash detection woes, but whatever your experience, it’s always good to have something to refer back to.

In this first installment, I’ll explain each of the parts of the Clash Detective interface.

The Clash Detective window allows you to specify rules and options for undertaking clash tests. In this window you can view results and generate clash reports.
The Test Panel is where you will find all of your clash tests. The test panel isn’t displayed by default, you need to click on the Add Test button in the clash detective. When you select the Add Test button, a new clash test will be created and added to the test panel.
Under the Rules tab, you can define rules in which Navisworks will use to ignore clashes, by default there are four pre-defined rules shown under the rules tab.
In the lower half of the clash detective window we have a section with a few tabs, the Select tab is the default view in the clash detective window. In this tab you can define the clash test by selecting multiple sets of items at a time. You could clash a whole model against a whole model, however this would be a very inefficient process, instead you can test clashes between different selection sets of elements in the model.

The Selection A and Selection B areas display all the items in a hierarchical list that replicates the selection tree window. You can select objects from these areas that will be tested against each other during a clash test.

Beneath the selection windows are a group of buttons which allow you to change what geometry is clashed in the test.

2014-11-29_7-59-59 When Surfaces is selected, surface geometry is included in the clash test. Surfaces is selected by default when you create a new clash test.
2014-11-29_8-00-15 When Lines is selected, line geometry is included in the clash test.
2014-11-29_8-00-28 When Points is selected, point geometry is included in the clash test
2014-11-29_8-08-55 Self Intersect is used to test the selected object against itself for clashes
2014-11-29_8-09-18 The Use Current Selection button is used to select objects directly in the scene view for clash tests
2014-11-29_8-09-31 The Select in Scene button is used to highlight the elements selected in the clash test. They will appear in blue when selected.


The Results tab is where you view the clash results. This tab is divided into three parts, the Results pane, Display Settings panel and the Items panel. By default the Display Settings and Items panels are hidden. They can be accessed by clicking on the panel title which is highlighted in the image.

The Results area displays a list of clash results in a tabbed format showing the name of the clash, the clash status, the date found and the description of the clash. If the clashes have a saved viewpoint, then the viewpoint icon will be displayed in the viewpoint column as well.

After expanding the Display Settings panel, you are provided with options to change which clash is highlighted, choose not to highlight the clashes at all, dim the other elements within the model so you only see those that are related to the particular clash as well as adjust basic viewpoint and simulation settings. 
Hidden at the bottom of the results tab is the Items panel. Once expanded you can view information on the clashing objects. The clash information displayed will depend on the select clash configuration.
Finally, in the Report tab you can adjust options for generating clash reports. The generated report will contain the details of all the clash results for the selected test. The report tab has three sections; Contents, Include Clashes and Output Settings.

In the Contents section, you can select the contents of the report, such as the date found, item numbers, grid locations, coordinates of the clash among others.

The Include Clashes section allows you to filter by new, active, reviewed, approved or resolved clashes.

The Output Settings section allows you to select the output format of your clash reports. It allows you to select either the reports from the current clash test or from all clash tests either as a combined or separated format. You can also choose from HTML, XML or recorded viewpoints as your clash report format.

In the next installment, I’ll build on what I’ve shown today and explain how to create selection sets to get better results from your clash tests.