The Group Clashes between element pairs within +/- field and associated mm/inch dimension radio group are for specifying the proximity of primitive clashes to be reported as a group. Because the specified values are 'plus or minus', the coordinate dimensions of the volume in which the clashes are considered to be a group are each twice the stated value. The default setting for the group distance between element pairs is 100mm, but it is common practice to have this value changed to 2000mm to make the clash grouping more effective. The decision to change the distance should be done only in consultation with the project discipline lead designers. The distance setting can be changed at any time during the project life cycle, but the clash groups must then be recomputed. Making fundamental changes to the group settings mid-project is not a recommended practice.

The Default Group Level drop-down lists are used to specify the level in the hierarchy at which the clashes are grouped within the appropriate discipline. For example, clashes within a pipe, may be reported at primitive level, at the branch level or at the pipe level. The defaults are PIPE-PIPE, EQUI-EQUI, STRU-SCTN, HVAC-HVAC, REST-REST and normally these are used. Clashes in other disciplines such as Hull and Room Design do not default to single levels and are handled by Group Rules described below.

The pane at the bottom of the tab is for specifying exceptions to the default group levels. The exceptions are defined under headings of GTYPE, Attribute, Value and Group Level. A Popup Menu is available (mouse right-click) with options of Add, Edit and Delete, used to add a new GTYPE and details, edit an existing GTYPE details, or remove an existing record. Up and Down buttons at the right-hand side of the pane are used to position the highlighted record in the list and hence determine its priority.

A recommended exception to the default group levels concerns modelling of service supports. In this case, although clashes are grouped by default at SCTN level for steelwork, for support steelwork the group should be at STRU level, as this is typically the owning level in the hierarchy for a support. To achieve this, the entry is: a GTYPE of ZONE, with Attribute PURP, Value SUPP and Group Level STRU.

A Group Rule with GTYPE * will allow clashes to be grouped at the level of any type entered under Group Level. For example, to group clashes with Hull objects at any of HPANEL, CPANEL, BLEVEL or BBLOCK, create four rules with entries as: GTYPE *, Attribute and Value left blank, Group Level HPANEL in the first rule, Group Level CPANEL in the second rule, and so on.

Other examples for Cableway and Room Design objects are shown in the picture above. The entry with GTYPE * and Group Level CWAY will group all clashes below cableways to the owning cableway. The entry with GTYPE * and Group Level ROOM will group all clashes below rooms to the owning room. The entry with GTYPE CTWALL and Group Level CTWALL will group clashes with constant thickness walls at that level, but note that clashes with CTWALL objects below ROOM objects will be grouped at ROOM level due to the earlier rule.