Encountering volumes is very costly

• for simple physics it can 80% of CPU time
• Must avoid intersection calculations

‘Smart voxels’ optimise intersections

• Much less need to tune geometry
• Can handle ‘flat’ CAD geometries

When geometry limits step

• Tracks are deposited on boundaries
• Reflection at boundaries is checked

Boundaries have thickness (‘tolerance’)

• track can be inside, outside or on surface

Volume entry and exit are determined

• logically, not numerically

Closely related to volume description

• replicated or placement volumes

Responsible for

• Volume Location
• Step Computation
  • currently these are tightly coupled

Physical Volume: positioned

• an instance of a logical volume placed in a mother logical volume

Logical Volume: solid+attributes

• Sensitive detector
• Visualisation properties

Solids: geometrical properties

• shape and size

Placement: it is one positioned volume

Replicated: a volume repeatedly placed

• Replica: simple repetition, like G3 divisions
• Parameterised: user-defined position, rotation, size (for simple solids only)

A mother volume can contain either

• one replicated volume OR
• many placement volumes

Hierarchy of volumes

Much repetition

• Volume & sub-tree

Up to millions of volumes for LHC era

Interchange with CAD systems

Location of point

Computation of step

• Linear intersection

Chord intersection

Types of Volumes

Navigator

Latest & future

Touchables

Joint activities

• Schedule Alpha-03 tag by end-97, addressing:
  • last developments and LCB milestones
  • PIIM directory restructuring (as in category diagram)
  • NT version
• Finalise CVS + tags + libs strategy
• Finalise documentation structure (starting from minutes of Spring mini-workshop)
• Decide strategy for external libs (CLHEP)

Working groups activities

• Review of POW for end-97 alpha-03
• Definition of POW for mid-98 beta-version
• Creation of “Examples working group”