Why do I sometime get inaccurate Clash Test distances

Issue

Solution

In Navisworks to optimize performance, all geometry is drawn using triangles. If you set the Render Mode to Hidden Line or Wireframe you will see how we draw your model.

Clash Detective will report the minimum distance one of the objects will need to move so the Clash no longer exist. With a Hard Clash this distance sees the intersecting triangles as separate objects, not as part of the whole face. 

This is a screenshot of a line intersecting a 6 sided object with the render style set to hidden line. Notice that each side of the object is made up of two triangles. Taking a point to point measure from where the line hits the surface to the nearest edge of the object, it is about .24m.  

 

However, the distance reported in the clash result is .06m. Taking a point to point measurement from the point where the line hits the surface to the nearest edge of the triangle it intersects, it is about .06m, which explains the distance value in the clash result.



You can get round this by using a hidden type of Clash Test called Hard (Conservative). To access this go to the Application Button > Options > Interface > Developer and check “Show internal properties”. 

When you go into Clash detective now you will have an additional test type named "Hard (Conservative)".

This reports all pairs of items, which might clash. This may give false positives in the results, but it is a safer and more thorough clash detection method.