SUBROUTINE MPINV(X1,Y1,X2,Y2,TT1,MC1,LSK,TT2,MC2,GDIST,GAZ12,GAZ21        
     1)                                                                         
C                                                                               
C        THIS SUBROUTINE WILL SOLVE THE INVERSE PROBLEM OF GEODETIC POSITIONING 
C      ON THE MAPPING PLANE.                                                    
C                                                                               
C                                                                               
C        INPUT:                                                                 
C                                                                               
C              X1,Y1 - X,Y COORDINATES OF THE INITIAL POINT.                    
C              X2 Y2 - X,Y,COORDINATES  OF POINT 2.                             
C              TT1 - T-TCORRECTION AT POINT 1.(IN RADIANS)                      
C              TT2 - T-TCORRECTION AT POINT 2.(IN RADIANS)                      
C              MC1 - MERIDIAN CONVERGENCE AT POINT 1.(IN RADIANS)               
C              MC2 - MERIDIAN CONVERGENCE AT POINT 2.(IN RADIANS)               
C              LSK - LINE SCALE FACTOR.                                         
C                                                                               
C        OUTPUT:                                                                
C                                                                               
C              GDIST - GEODESIC DISTANCE.                                       
C              GEODETIC AZIMUTH (IN RADIANS).                                   
C                                                                               
C                                           WRITTEN BY G.BOWIE, DEC. 1977.      
C                                                                               
      IMPLICIT REAL*8 (A-Z)                                                     
      MPDIST=DSQRT((X2-X1)**2+(Y2-Y1)**2)                                       
      MPAZ=DATAN2((X2-X1),(Y2-Y1))                                              
      MPAZ2=DATAN2((X1-X2),(Y1-Y2))                                             
      GDIST=MPDIST/LSK                                                          
      GAZ12=MPAZ+TT1+MC1                                                        
      GAZ21=MPAZ2+TT2+MC2                                                       
      RETURN                                                                    
      END