Generate view transformation matrices.

  A=VIEWMTX(AZ,EL) returns the 4x4 orthographic transformation 

  matrix, A, used to project 3-D vectors onto the 2-D plot surface. 

  Uses the same definition for azumith and elevation as VIEW1HRQVU2, in

  particular, AZ and EL must be in degrees.  Returns the same 

  transformation matrix as the commands


      A = VIEW1HRQVU2

  but doesn't change the current VIEW1HRQVU2.



  A=VIEWMTX(AZ,EL,PHI) returns a 4x4 perspective transformation

  matrix used to project 3-D vectors onto the 2-D plot surface.

  PHI is the subtended view angle of the normalized plot cube 

  (in degrees) and controls the amount of perspective distortion:

      PHI =  0 degrees is orthographic projection

      PHI = 10 degrees is like a telephoto lens

      PHI = 25 degrees is like a normal lens

      PHI = 60 degrees is like a wide angle lens

  The matrix A can be used to set the view transformation using




  A=VIEWMTX(AZ,EL,PHI,XC) returns the perspective transformation

  matrix using XC as the target (or look-at) point within

  the normalized plot cube.  XC=[xc,yc,zc] specifies the 

  point (xc,yc,zc) in the plot cube.  The default value is

  the closest point in the plot cube,



  XC = 0.5+sqrt(3)/2*[cos(EL)*sin(AZ),-cos(EL)*cos(AZ),sin(EL)].



  See also VIEW1HRQVU2.