library: libGeom #include "TGeoPolygon.h"

# TGeoPolygon

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

## class TGeoPolygon : public TObject

| Inheritance Chart:

`TObject`

<-

`TGeoPolygon`

        private:

            void ConvexCheck()
          Bool_t IsRightSided(Double_t* point, Int_t ind1, Int_t ind2) const
          Bool_t IsSegConvex(Int_t i1, Int_t i2 = -1) const
            void OutscribedConvex()

        public:

                          TGeoPolygon()
                          TGeoPolygon(Int_t nvert)
                          TGeoPolygon(const TGeoPolygon&)
                  virtual ~TGeoPolygon()
           static TClass* Class()
                   Bool_t Contains(Double_t* point) const
                     void FinishPolygon()
                    Int_t GetNvert() const
                Double_t* GetX()
                Double_t* GetY()
          virtual TClass* IsA() const
                   Bool_t IsConvex() const
                   Bool_t IsFinished() const
             TGeoPolygon& operator=(const TGeoPolygon&)
                 Double_t Safety(Double_t* point, Int_t& isegment) const
                     void SetConvex(Bool_t flag = kTRUE)
                     void SetNextIndex(Int_t index = -1)
                     void SetXY(Double_t* x, Double_t* y)
             virtual void ShowMembers(TMemberInspector& insp, char* parent)
             virtual void Streamer(TBuffer& b)
                     void StreamerNVirtual(TBuffer& b)

### Data Members

        protected:

               Int_t fNvert      number of vertices (must be defined clockwise in XY plane)
               Int_t fNconvex    number of points of the outscribed convex polygon
              Int_t* fInd        [fNvert] list of vertex indices
              Int_t* fIndc       [fNconvex] indices of vertices of the outscribed convex polygon
           Double_t* fX          ! pointer to list of current X coordinates of vertices
           Double_t* fY          ! pointer to list of current Y coordinates of vertices
          TObjArray* fDaughters  list of concave daughters

        public:

          static const enum TGeoPolygon:: kGeoConvex
          static const enum TGeoPolygon:: kGeoFinishPolygon

## Class Description

     TGeoPolygon - Arbitrary polygon class
    ____________________________________________________________________________

     A polygon is a 2D shape defined by vertices in the XY plane. It is used by
     TGeoXtru class for computing Contains() and Safety(). Only the pointers to
     the actual lists of XY values are used - these are not owned by the class.

     To check if a point in XY plane is contained by a polygon, this is splitted
     into an outscribed convex polygon and the remaining polygons of its subtracton
     from the outscribed one. A point is INSIDE if it is
     contained by the outscribed polygon but NOT by the remaining ones. Since these
     can also be arbitrary polygons at their turn, a tree structure is formed:

      P = Pconvex - (Pconvex-P)           where (-) means 'subtraction'
      Pconvex-P = P1 + P2 + ...           where (+) means 'union'

      *Note that P1, P2, ... do not intersect each other and they are defined
       by subsets of the list of vertices of P. They can be splitted in the same
       way as P*

     Therefore, if C(P) represents the Boolean : 'does P contains a given point?',
     then:

     C(P) = C(Pconvex) .and. not(C(P1) | C(P2) | ...)

     For creating a polygon without TGeoXtru class, one has to call the constructor
     TGeoPolygon(nvert) and then SetXY(Double_t *x, Double_t *y) providing the
     arrays of X and Y vertex positions (defined clockwise) that have to 'live' longer
     than the polygon they will describe. This complication is due to efficiency reasons.
     At the end one has to call the FinishPolygon() method.

TGeoPolygon()

     Dummy constructor.

TGeoPolygon(Int_t nvert)

     Default constructor.

~TGeoPolygon()

     Destructor

Bool_t Contains(Double_t *point) const

     Check if a point given by X = point[0], Y = point[1] is inside the polygon.

void ConvexCheck()

     Check polygon convexity.

void FinishPolygon()

Bool_t IsRightSided(Double_t *point, Int_t ind1, Int_t ind2) const

     Check if POINT is right-sided with respect to the segment defined by IND1 and IND2.

Bool_t IsSegConvex(Int_t i1, Int_t i2) const

     Check if a segment [0..fNvert-1] belongs to the outscribed convex pgon.

void OutscribedConvex()

     Compute indices for the outscribed convex polygon.

Double_t Safety(Double_t *point, Int_t &isegment) const

     Compute minimum distance from POINT to any segment. Returns segment index.

void SetNextIndex(Int_t index)

     Sets the next polygone index. If index<0 sets all indices consecutive
     in increasing order.

void SetXY(Double_t *x, Double_t *y)

     Set X/Y array pointer for the polygon and daughters.

### Inline Functions

                   Int_t GetNvert() const
               Double_t* GetX()
               Double_t* GetY()
                  Bool_t IsConvex() const
                  Bool_t IsFinished() const
                    void SetConvex(Bool_t flag = kTRUE)
                 TClass* Class()
                 TClass* IsA() const
                    void ShowMembers(TMemberInspector& insp, char* parent)
                    void Streamer(TBuffer& b)
                    void StreamerNVirtual(TBuffer& b)
             TGeoPolygon TGeoPolygon(const TGeoPolygon&)
            TGeoPolygon& operator=(const TGeoPolygon&)

Author: Mihaela Gheata 5/01/04
Last update: root/geom:$Name: $:$Id: TGeoPolygon.cxx,v 1.4 2005/05/17 12:00:23 brun Exp $
Copyright (C) 1995-2000, Rene Brun and Fons Rademakers. *