library: libGeom #include "TGeoVolume.h"

# TGeoVolumeAssembly

class description - source file - inheritance tree (.pdf)

## class TGeoVolumeAssembly : public TGeoVolume

| Inheritance Chart:
`TObject`
| <- | `TNamed`
`TGeoAtt`
`TAttLine`
`TAttFill`
`TAtt3D`
| <- | `TGeoVolume`
| <- | `TGeoVolumeAssembly` |

        public:

                              TGeoVolumeAssembly()
                              TGeoVolumeAssembly(const char* name)
                              TGeoVolumeAssembly(const TGeoVolumeAssembly&)
                      virtual ~TGeoVolumeAssembly()
                 virtual void AddNode(const TGeoVolume* vol, Int_t copy_no, TGeoMatrix* mat = 0, Option_t* option = "")
                 virtual void AddNodeOverlap(const TGeoVolume* vol, Int_t copy_no, TGeoMatrix* mat, Option_t* option)
               static TClass* Class()
          virtual TGeoVolume* Divide(const char* divname, Int_t iaxis, Int_t ndiv, Double_t start, Double_t step, Int_t numed = 0, Option_t* option = "")
                 virtual void DrawOnly(Option_t*)
                virtual Int_t GetCurrentNodeIndex() const
                virtual Int_t GetNextNodeIndex() const
              virtual TClass* IsA() const
               virtual Bool_t IsAssembly() const
               virtual Bool_t IsVisible() const
          TGeoVolumeAssembly& operator=(const TGeoVolumeAssembly&)
                         void SetCurrentNodeIndex(Int_t index)
                         void SetNextNodeIndex(Int_t index)
                 virtual void ShowMembers(TMemberInspector& insp, char* parent)
                 virtual void Streamer(TBuffer& b)
                         void StreamerNVirtual(TBuffer& b)

### Data Members

        private:

          Int_t fCurrent  ! index of current selected node
          Int_t fNext     ! index of next node to be entered

## Class Description

       TGeoVolume - the base class representing solids.

       Volumes are the basic objects used in building the geometrical hierarchy.
     They represent unpositioned objects but store all information about the
     placement of the other volumes they may contain. Therefore a volume can
     be replicated several times in the geometry. In order to create a volume, one
     has to put togeather a shape and a medium which are already defined. Volumes
     have to be named by users at creation time. Every different name may represent a
     an unique volume object, but may also represent more general a family (class)
     of volume objects having the same shape type and medium, but possibly
     different shape parameters. It is the user's task to provide different names
     for different volume families in order to avoid ambiguities at tracking time.
     A generic family rather than a single volume is created only in two cases :
     when a generic shape is provided to the volume constructor or when a division
     operation is applied. Each volume in the geometry stores an unique
     ID corresponding to its family. In order to ease-up their creation, the manager
     class is providing an API that allows making a shape and a volume in a single step.

       Volumes are objects that can be visualized, therefore having visibility,
     colour, line and fill attributes that can be defined or modified any time after
     the volume creation. It is advisable however to define these properties just
     after the first creation of a volume namespace, since in case of volume families
     any new member created by the modeler inherits these properties.

        In order to provide navigation features, volumes have to be able to find
     the proper container of any point defined in the local reference frame. This
     can be the volume itself, one of its positioned daughter volumes or none if
     the point is actually outside. On the other hand, volumes have to provide also
     other navigation methods such as finding the distances to its shape boundaries
     or which daughter will be crossed first. The implementation of these features
     is done at shape level, but the local mother-daughters management is handled
     by volumes that builds additional optimisation structures upon geometry closure.
     In order to have navigation features properly working one has to follow the
     general rules for building a valid geometry (see TGeoManager class).

       Now let's make a simple volume representing a copper wire. We suppose that
     a medium is already created (see TGeoMedium class on how to create media).
     We will create a TUBE shape for our wire, having Rmin=0cm, Rmax=0.01cm
     and a half-length dZ=1cm :

       TGeoTube *tube = new TGeoTube("wire_tube", 0, 0.01, 1);

     One may ommit the name for the shape if no retreiving by name is further needed
     during geometry building. The same shape can be shared by different volumes
     having different names and materials. Now let's make the volume for our wire.
     The prototype for volumes constructor looks like :

       TGeoVolume::TGeoVolume(const char *name, TGeoShape *shape, TGeoMedium *med)

     Since TGeoTube derives brom the base shape class, we can provide it to the volume
     constructor :

       TGeoVolume *wire_co = new TGeoVolume("WIRE_CO", tube, ptrCOPPER);

     Do not bother to delete neither the media, shapes or volumes that you have
     created since all will be automatically cleaned on exit by the manager class.
     If we would have taken a look inside TGeoManager::MakeTube() method, we would
     have been able to create our wire with a single line :

       TGeoVolume *wire_co = gGeoManager->MakeTube("WIRE_CO", ptrCOPPER, 0, 0.01, 1);

     The same applies for all primitive shapes, for which there can be found
     corresponding MakeSHAPE() methods. Their usage is much more convenient unless
     a shape has to be shared between more volumes. Let's make now an aluminium wire
     having the same shape, supposing that we have created the copper wire with the
     line above :

       TGeoVolume *wire_al = new TGeoVolume("WIRE_AL", wire_co->GetShape(), ptrAL);

     Now that we have learned how to create elementary volumes, let's see how we
     can create a geometrical hierarchy.

       Positioning volumes
     -----------------------

       When creating a volume one does not specify if this will contain or not other
     volumes. Adding daughters to a volume implies creating those and adding them
     one by one to the list of daughters. Since the volume has to know the position
     of all its daughters, we will have to supply at the same time a geometrical
     transformation with respect to its local reference frame for each of them.
     The objects referencing a volume and a transformation are called NODES and
     their creation is fully handled by the modeler. They represent the link
     elements in the hierarchy of volumes. Nodes are unique and distinct geometrical
     objects ONLY from their container point of view. Since volumes can be replicated
     in the geometry, the same node may be found on different branches.

/* */

       An important observation is that volume objects are owned by the TGeoManager
     class. This stores a list of all volumes in the geometry, that is cleaned
     upon destruction.

       Let's consider positioning now our wire in the middle of a gas chamber. We
     need first to define the gas chamber :

       TGeoVolume *chamber = gGeoManager->MakeTube("CHAMBER", ptrGAS, 0, 1, 1);

     Now we can put the wire inside :

       chamber->AddNode(wire_co, 1);

     If we inspect now the chamber volume in a browser, we will notice that it has
     one daughter. Of course the gas has some container also, but let's keep it like
     that for the sake of simplicity. The full prototype of AddNode() is :

       TGeoVolume::AddNode(TGeoVolume *daughter, Int_t usernumber,
                           TGeoMatrix *matrix=gGeoIdentity)

     Since we did not supplied the third argument, the wire will be positioned with
     an identity transformation inside the chamber. One will notice that the inner
     radii of the wire and chamber are both zero - therefore, aren't the two volumes
     overlapping ? The answer is no, the modeler is even relaying on the fact that
     any daughter is fully contained by its mother. On the other hand, neither of
     the nodes positioned inside a volume should overlap with each other. We will
     see that there are allowed some exceptions to those rules.

     Overlapping volumes
     --------------------

       Positioning volumes that does not overlap their neighbours nor extrude
     their container is sometimes quite strong contrain. Some parts of the geometry
     might overlap naturally, e.g. two crossing tubes. The modeller supports such
     cases only if the overlapping nodes are declared by the user. In order to do
     that, one should use TGeoVolume::AddNodeOverlap() instead of TGeoVolume::AddNode().
       When 2 or more positioned volumes are overlapping, not all of them have to
     be declared so, but at least one. A point inside an overlapping region equally
     belongs to all overlapping nodes, but the way these are defined can enforce
     the modeler to give priorities.
       The general rule is that the deepest node in the hierarchy containing a point
     have the highest priority. For the same geometry level, non-overlapping is
     prioritized over overlapping. In order to illustrate this, we will consider
     few examples. We will designate non-overlapping nodes as ONLY and the others
     MANY as in GEANT3, where this concept was introduced:
       1. The part of a MANY node B extruding its container A will never be "seen"
     during navigation, as if B was in fact the result of the intersection of A and B.
       2. If we have two nodes A (ONLY) and B (MANY) inside the same container, all
     points in the overlapping region of A and B will be designated as belonging to A.
       3. If A an B in the above case were both MANY, points in the overlapping
     part will be designated to the one defined first. Both nodes must have the
     same medium.
       4. The silces of a divided MANY will be as well MANY.

     One needs to know that navigation inside geometry parts MANY nodes is much
     slower. Any overlapping part can be defined based on composite shapes - this
     is always recommended.

TGeoVolumeAssembly() :TGeoVolume()

TGeoVolumeAssembly(const char *name) :TGeoVolume(name, NULL, NULL)

void AddNode(const TGeoVolume *vol, Int_t copy_no, TGeoMatrix *mat, Option_t *option)

     Add a component to the assembly.

void AddNodeOverlap(const TGeoVolume *, Int_t, TGeoMatrix *, Option_t *)

TGeoVolume* Divide(const char *, Int_t, Int_t, Double_t, Double_t, Int_t, Option_t *)

### Inline Functions

                           void ~TGeoVolumeAssembly()
                           void DrawOnly(Option_t*)
                          Int_t GetCurrentNodeIndex() const
                          Int_t GetNextNodeIndex() const
                         Bool_t IsAssembly() const
                         Bool_t IsVisible() const
                           void SetCurrentNodeIndex(Int_t index)
                           void SetNextNodeIndex(Int_t index)
                        TClass* Class()
                        TClass* IsA() const
                           void ShowMembers(TMemberInspector& insp, char* parent)
                           void Streamer(TBuffer& b)
                           void StreamerNVirtual(TBuffer& b)
             TGeoVolumeAssembly TGeoVolumeAssembly(const TGeoVolumeAssembly&)
            TGeoVolumeAssembly& operator=(const TGeoVolumeAssembly&)

Author: Andrei Gheata 30/05/02
Last update: root/geom:$Name: $:$Id: TGeoVolume.cxx,v 1.64 2005/06/27 13:09:47 brun Exp $
Copyright (C) 1995-2000, Rene Brun and Fons Rademakers. *