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If you use either of the aggregate tools, you will get a popup asking you to specify the name of the aggregate. By default this is globalVolumeAggregate. When you accept, the tool will add ri_volume_aggregate and ri_volume_dsominmax to your obj with the given aggregate name.
You may instead want to specify volume aggregates on the Geometry level. To do this, you will need to add a primitive attribute called ri_volume_aggregate.
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