Calculate angle between 2 points

C call:

C     CALL PTH048 (X1,Y1,X2,Y2,RW,IRET)

C     

C     The following variables must be defined beforehand:

C     

C     X1/Y1 : Coordinate first point

C     X2/Y2 : Coordinate second point

C     RW    : Angle (return value)

C     IRET  : is not evaluated, but must be specified

C     

C     Example:

C     --------------------------------------

C     Calculate angle between two points

C     --------------------------------------

      X1 = 50.0

      Y1 = 50.0

      X2 = 80.0

      Y2 = 100.0

      CALL PTH048 (X1,Y1,X2,Y2,RW,IRET)