class TView3D: public TView

 Default constructor

 TView3D constructor

  Creates a 3-D view in the current pad
  rmin[3], rmax[3] are the limits of the object depending on
  the selected coordinate system

  Before drawing a 3-D object in a pad, a 3-D view must be created.
  Note that a view is automatically created when drawing legos or surfaces.

  The coordinate system is selected via system:
   system = 1  Cartesian
   system = 2  Polar
   system = 3  Cylindrical
   system = 4  Spherical
   system = 5  PseudoRapidity/Phi

 Copy constructor.

 Assignment operator.

 TView3D default destructor.

 Define axis vertices.

    Input  ANG     - angle between X and Y axis

    Output: AV(3,8) - axis vertices
            IX1     - 1st point of X-axis
            IX2     - 2nd point of X-axis
            IY1     - 1st point of Y-axis
            IY2     - 2nd point of Y-axis
            IZ1     - 1st point of Z-axis
            IZ2     - 2nd point of Z-axis


                     8                        6
                    / \                      /|\
                 5 /   \ 7                5 / | \ 7
                  |\   /|                  |  |  |
      THETA < 90  | \6/ |     THETA > 90   | /2\ |
      (Top view)  |  |  |   (Bottom view)  |/   \|
                 1 \ | /3                 1 \   /3
                    \|/                      \ /
                     2                        4

 Define perspective view.

 Compute transformation matrix from world coordinates
 to normalised coordinates (-1 to +1)
   Input :
      theta, phi - spherical angles giving the direction of projection
      psi - screen rotation angle
      cov[3] - center of view
      dview - distance from COV to COP (center of projection)
      umin, umax, vmin, vmax - view window in projection plane
      dproj - distance from COP to projection plane
      bcut, fcut - backward/forward range w.r.t projection plane (fcut<=0)
   Output :
      nper[16] - normalizing transformation
 compute tr+rot to get COV in origin, view vector parallel to -Z axis, up
 vector parallel to Y.

                         ^Yv   UP ^  proj. plane
                        |        |   /|
                       |        |  /  |
                      |   dproj  /  x--- center of window (COW)
                 COV |----------|--x--|------------> Zv
                              /           | VRP'z
                       /   --->      |  /
                /     VPN       |/
               Xv

   1 - translate COP to origin of MARS : Tper = T(-copx, -copy, -copz)
   2 - rotate VPN : R = Rz(-psi)*Rx(-theta)*Rz(-phi) (inverse Euler)
   3 - left-handed screen reference to right-handed one of MARS : Trl

   T12 = Tper*R*Trl

 Define view direction (in spherical coordinates)

              Compute transformation matrix from world coordinates
              to normalised coordinates (-1 to +1)

    Input: S(3)    - scale factors
           C(3)    - centre of scope
           COSPHI  - longitude COS
           SINPHI  - longitude SIN
           COSTHE  - latitude COS (angle between +Z and view direc.)
           SINTHE  - latitude SIN
           COSPSI  - screen plane rotation angle COS
           SINPSI  - screen plane rotation angle SIN

 Draw the outline of a cube while rotating a 3-d object in the pad.

 Execute action corresponding to one event.

 Execute action corresponding to one event.

  This member function is called when a object is clicked with the locator

  If Left button clicked in the object area, while the button is kept down
  the cube representing the surrounding frame for the corresponding
  new latitude and longitude position is drawn.

 Find Z component of NORMAL in normalized coordinates.

    Input: X - X-component of NORMAL
           Y - Y-component of NORMAL
           Z - Z-component of NORMAL

    Output: ZN - Z-component of NORMAL in normalized coordinates

 Find critical PHI sectors.

    Input: IOPT    - options: 1 - from BACK to FRONT 'BF'
                              2 - from FRONT to BACK 'FB'
           KPHI    - number of phi sectors
           APHI(*) - PHI separators (modified internally)

    Output: IPHI1  - initial sector
            IPHI2  - final sector

 Find critical THETA sectors for given PHI sector.

    Input: IOPT        - options: 1 - from BACK to FRONT 'BF'
                                  2 - from FRONT to BACK 'FB'
           PHI         - PHI sector
           KTH         - number of THETA sectors
           ATH(*)      - THETA separators (modified internally)

    Output: ITH1  - initial sector
            ITH2  - final sector

 Find centre of a MIN-MAX scope and scale factors

    Output: SCALE(3)  - scale factors
            CENTER(3) - centre
            IREP      - reply (-1 if error in min-max)

 Return distance to axis from point px,py.

  Algorithm:

       A(x1,y1)         P                             B(x2,y2)
       ------------------------------------------------
                        I
                        I
                        I
                        I
                       M(x,y)

  Let us call  a = distance AM     A=a**2
               b = distance BM     B=b**2
               c = distance AB     C=c**2
               d = distance PM     D=d**2
               u = distance AP     U=u**2
               v = distance BP     V=v**2     c = u + v

  D = A - U
  D = B - V  = B -(c-u)**2
     ==> u = (A -B +C)/2c

 Get maximum view extent.

 Get Range function.

 Get Range function.

 Get current window extent.

 Check if point is clipped in perspective view.

 Transfer point from normalized to world coordinates.

    Input: PN(3) - point in world coordinate system
           PW(3) - point in normalized coordinate system

 Transfer point from normalized to world coordinates.

    Input: PN(3) - point in world coordinate system
           PW(3) - point in normalized coordinate system

 Transfer vector of NORMAL from word to normalized coordinates.

    Input: PW(3) - vector of NORMAL in word coordinate system
           PN(3) - vector of NORMAL in normalized coordinate system

 Transfer vector of NORMAL from word to normalized coordinates.

    Input: PW(3) - vector of NORMAL in word coordinate system
           PN(3) - vector of NORMAL in normalized coordinate system

 Set the correct window size for lego and surface plots.

  Set the correct window size for lego and surface plots.
  And draw the background if necessary.

    Input parameters:

   RBACK : Background colour

 Store axis coordinates in the NDC system.

 Set default viewing window.

 This is a function which creates default outline.

      x = fRmin[0]        X = fRmax[0]
      y = fRmin[1]        Y = fRmax[1]
      z = fRmin[2]        Z = fRmax[2]


               (x,Y,Z) +---------+ (X,Y,Z)
                      /         /|
                     /         / |
                    /         /  |
           (x,y,Z) +---------+   |
                   |         |   + (X,Y,z)
                   |         |  /
                   |         | /
                   |         |/
                   +---------+
                (x,y,z)   (X,y,z)

 Set the parallel option (default).

 Set perspective option.

 Set Range function.

 Set 3-D View range.

 Input:  x0, y0, z0 are minimum coordinates
         x1, y1, z1 are maximum coordinates

         flag values are: 0 (set always) <- default
                          1 (shrink view)
                          2 (expand view)

 Set viewing window.

 Set view parameters.

 Recompute window for perspective view.

 Set view direction (in spherical coordinates).

    Input  PHI     - longitude
           THETA   - latitude (angle between +Z and view direction)
           PSI     - rotation in screen plane

    Output: IREP   - reply (-1 if error in min-max)

    Errors: error in min-max scope

 Transfer point from world to normalized coordinates.

    Input: PW(3) - point in world coordinate system
           PN(3) - point in normalized coordinate system

 Transfer point from world to normalized coordinates.

    Input: PW(3) - point in world coordinate system
           PN(3) - point in normalized coordinate system

 Force the current pad to be updated.

 API to rotate view and adjust the pad provided it the current one.

 Set to side view.

 Set to front view.

 Set to top view.

 Turn on /off 3D axis.

 Turn on /off the interactive option to
  Zoom / Move / Change attributes of 3D axis correspond this view.

 Adjust all sides of view in respect of the biggest one.

 Move view into the center of the scene.

 unZOOM this view.

 ZOOM this view.

 Move focus to a different box position and extent in nsteps. Perform
 rotation with dlat,dlong,dpsi at each step.

 'a' increase scale factor (clip cube borders)
 's' decrease scale factor (clip cube borders)

 Move view window :
 l,L - left
 h,H - right
 u,U - down
 i,I - up

 Zoom in.

 Zoom out.

 Stream an object of class TView3D.