To select items for a clash test
 Tools panel
Tools panel  Clash Detective
Clash Detective .
. There are two identical panes in this tab called Selection A and Selection B. These panes contain tree views of two sets of items that will be tested against each other during the clash test, and you need to select items in each. You can select the items by choosing an option from the drop-down list for each selection tree and manually selecting items from the tree hierarchies. Any selection sets in the scene are also available from the drop-down list, which is a quick and useful method of setting up items across sessions (see Interactive Geometry Selection).
You can also transfer the current selection to one of the selection panes by selecting items in the usual way in the Scene View or Selection Tree and clicking the appropriate Use Current Selection button  .
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 to test the corresponding set for self-intersection, as well as intersection against the other set.
 to test the corresponding set for self-intersection, as well as intersection against the other set. So, for example, if you want to run a clash test between some surface geometry and a point cloud, you can set up the geometry in the Selection A pane, and click the Point Cloud  button under the Selection B pane. The Surface
 button under the Selection B pane. The Surface  button under the Selection A pane is toggled on by default. Additionally, you could set the clash Type to Clearance with a Tolerance of 1 meter.
 button under the Selection A pane is toggled on by default. Additionally, you could set the clash Type to Clearance with a Tolerance of 1 meter.