Clash FAQ
- What is the clash tolerance setting for automatic clash detection in Model Coordination?
- Why are clash counts different between Model Coordination and Navisworks?
- Why do I need to select content to see clashes, rather than clashes automatically loading?
- Can I use search sets to define what to clash?
- What happens if a search set used in a clash check is deleted?
- Why aren't clashes within the same model showing up?
- What is an unsuccessful clash check?
- How can I fix an unsuccessful clash check?
- Why can I see my latest models in Clash Settings, but not in the rest of Model Coordination?
- What is the yellow warning icon in my coordination space?
- Why can I see clashes between two objects that are at different levels and aren't intersecting?
- Has the camera behavior changed when entering the viewer to review clashes?
What is the clash tolerance setting for automatic clash detection in Model Coordination?
Automatic clash detection in Model Coordination uses a fixed tolerance of 0.5 mm (0.0005 m). This value is not currently configurable.
After clashes are detected, you can still apply a tolerance-based filter while reviewing results in the viewer. This helps you focus on clashes above or below a chosen penetration depth, but it does not change the underlying clash detection results. See View and Filter Clashes.
If you compare results with Navisworks, use the same tolerance value (0.5 mm) to reduce differences in clash counts.
Using a tolerance of 0.0 mm can produce extra clashes that are often not meaningful for coordination (for example, objects that are effectively touching on the same geometry plane).
Why are clash counts different between Model Coordination and Navisworks?
Different clash counts are usually caused by differences in clash settings, especially tolerance.
Model Coordination uses a fixed tolerance of 0.5 mm (0.0005 m). If Navisworks is set to 0.0 mm, it can report additional clashes that Model Coordination does not show.
To make results more comparable:
- Set Navisworks clash tolerance to 0.5 mm.
- Confirm you are comparing the same model versions and the same model set.
- Re-run clash checks after changing settings.
Small differences can still occur based on workflow and model setup, but aligning tolerance typically resolves the largest discrepancies.
Why do I need to select content to see clashes, rather than clashes automatically loading?
Previously in Model Coordination, we preloaded all detailed clash information when opening the product. This could result in long loading times and reduced performance. To improve this, we only download detailed clash information when it is requested in the viewer, improving the performance and scalability of clash-on coordination spaces.
Most the Model Coordination workflows remain the same, with these minor changes:
- We no longer preload clash data when opening more than two models in the viewer. This means when clicking a row in the clash grid that contains more than two models, clash data will not be preloaded.
- We still automatically preload clash data in the viewer when there are only two models. This means that when choosing a cell in the clash grid, we will preload the clashes as usual.
- When entering the Clashes panel in the viewer, either by loading content from the Models tool or the Views tool, you must now select the content you want to clash, before seeing any clash results.
Can I use search sets to define what to clash?
Yes. Selection A and Selection B can each contain either models or search sets. To combine the two, use models in one selection and search sets in the other. When you choose multiple search sets in a selection, they're joined with an or operator.
All search sets you have access to are available. If you later update a search set, clash checks that use it automatically use the new definition. See Select content to clash.
What happens if a search set used in a clash check is deleted?
Deleting a search set doesn't break existing clash checks. The deleted search set stays in any clash check that already uses it, but you can't add it to new clash checks or reuse it elsewhere. Deletion is a soft delete.
Why aren't clashes within the same model showing up?
Model Coordination doesn't detect clashes between objects in the same model. This applies even when you clash two search sets, if the matching objects all belong to one model.
For example, the model MyHouse.rvt - Electrical might contain both lighting fixtures and sound devices. If you clash a Lighting fixtures search set against a Sound Devices search set, you see no clashes, because both sets resolve to objects in the same model.
To detect these clashes, separate the objects into different Revit 3D views or files.
What is an unsuccessful clash check?
A clash check is unsuccessful when it fails or times out. The most common reason is because there is too much clash data, caused by:
- Many models in the coordination space.
- Models of large sizes.
- Models with complex geometry resulting in a high number of clashes.
- Models with similar or duplicate geometry resulting in a high number of clashes.
Even if a clash check is successful, too much clash data can negatively impact performance. Signs that there is a large amount of clash data include:
- The Clashes column in the Models tool takes a while (ten or more seconds) to load.
- The Clashes panel in the viewer takes several seconds to load, or does not load at all.
- There are many models turned on for automatic clash detection. While clash success is also dependent on each models' complexity and size, unsuccessful clash checks become more common when there are 450 or more models included in the clash check.
- The numbers in the Clashes column and clash grid are large (more than 10000 clashes across many models).
- Different models in the clash grid show similar clash counts, suggesting that they may be duplicates.
If the latest clash check is unsuccessful, Model Coordination will show one of two error messages by the coordination space picker:
| Error | Details |
|---|---|
| Can't display latest models | The clash check on the latest models has failed, so Model Coordination shows the models involved in the most recent successful clash check. This means Model Coordination could be showing older model versions, models that have since been deleted from the folder, or be missing newer models which are in the folder.  |
| Clash check unsuccessful | This means that there has never been a successful clash check in the coordination space. Model Coordination shows the latest models in the coordination space, but without any clash results.  |
How can I fix an unsuccessful clash check?
Most unsuccessful clash checks are due to an excessive amount of clash data. One way project administrators can reduce clash data is by removing duplicate or redundant content from the clash check:
- If you have models representing each area or level of a project, and also a federated model containing all of those individual models again, try turning off clash for the federated model. Alternatively, remove the federated model from the coordination space.
- If you've uploaded models containing linked models, try creating object exclusions that exclude the linked model content from clash. Alternatively, recreate the 3D views without any linked models.
- If you have the same components or systems, for example walls, represented in multiple models or views, try turning off clash for the redundant models, or creating object exclusions to exclude specific objects from clash.
If you have subfolders containing duplicate or similar models to other folders in the coordination space (for example, Consumed folders containing models from another Team folder), change the coordination space settings to remove the redundant subfolders.
Other ways to reduce the amount of clash data include:
- Creating object exclusions to remove objects from clash that are not a priority for coordination, such as bolts, flex ducts, and hangers.
- Creating multiple coordination spaces and having fewer models in each. For example, create a coordination space for each building in a project, or for each level of a building, or phase of a project.
- Reducing the size of your models. For example, publish fewer views from your Revit models.
There are also various causes that can't be solved by reducing model numbers or size, or changing your coordination space setup. If these troubleshooting steps don't work, or you experience a spinner on the Clashes tab that doesn't resolve, the support team can investigate and help to resolve the error.
Why can I see my latest models in Clash Settings, but not in the rest of Model Coordination?
The Clashes > Settings page always shows the models involved in the last clash check, whether the clash check was successful or not.
If the last clash check failed, Model Coordination may be showing models from a previous successful clash check, while the Clash Settings page shows the models from the failed clash check. This would mean that the Clash Settings page shows a more up-to-date list of models than the rest of Model Coordination.
Data in the Clashes column will reflect the last successful clash check, even inside Clash Settings.
What is the yellow warning icon in my coordination space?
If you see this icon 
on the coordination space picker, it means that the clash check has processed successfully overall, but certain models couldn't be checked.
The specific models will be marked with the yellow warning icon next to the model's name in the Models and Clashes tools. These models do not show any clash data, because something has gone wrong when processing the models for clash.
This is often due to temporary problems and can be resolved by simply uploading the model again to Forma Data Management. Try this before attempting another solution. If reuploading the model does not solve the problem, then contact support.
Why can I see clashes between two objects that are at different levels and aren't intersecting?
Applies to
This scenario only applies when all the following criteria are fulfilled:
- The affected file is a Revit file.
- It's in a V2 coordination space.
- The Revit file is broken down into Revit views (for example, by level) and an object in the model spans multiple views.
Example
A common example is a column or wall that extends through multiple levels, with a Revit view defined for each level. These kinds of objects can show as clashing against another object that they are not visibly touching due to the objects clashing in a different Revit view.
Reason
Clash in V2 coordination spaces uses the Revit master model view (all the geometry in the Revit file) instead of using the model geometry in each Revit view. We use the master model view to optimize clash performance.
Model Coordination clash is based on object IDs, and when an object spans multiple Revit views it will still retain the same object ID. Clashes in the viewer are then shown by highlighting the two objects (based on the object IDs). This can result in two objects which may not be visibly touching showing as a clash, due to these objects clashing in a different Revit view.
Remove the clashes by
When a clash is noted as an issue or not an issue, all instances of this clash will be removed across multiple Revit views.
Has the camera behavior changed when entering the viewer to review clashes?
Previously, when navigating to the Clashes tab from another tab in the viewer, the camera orientation would reset to a plan view. Similarly, when selecting a clash in the viewer panel, or creating an issue or non-issue, the camera orientation would change to look from the South-East corner.
To reduce potential disorientation and loss of context, the camera now remains in its original, user-specified position by default. If you prefer the previous camera positions, use the ViewCube to change orientations as required.