SUBROUTINE TTLS(A,B,PHI1,DIST,X1,Y1,X2,Y2,XO,SF,TT,LS)                    
C                                                                               
C        THIS SUBROUTINE WILL COMPUTE THE T-T AND LINE SCALE CORRECTIONS IN     
C      A TRANSVERSE MERCATOR PROJECTION.                                        
C                                                                               
C        INPUT:                                                                 
C              A,B - SEMI-MAJOR AND SEMI-MINOR AXES OF THE REFERENCE ELLIPSOID. 
C              PHI1 - GEODETIC LATITUDE OF POINT 1.                             
C              DIST - GEODESIC DISTANCE FROM POINT 1 TO 2.                      
C              X1,Y1,X2,Y2 - X,Y,COORDINATES OF POINTS 1 AND 2.                 
C              X1,Y1,X2,Y2 - X,Y COORDINATES OF POINTS 1 AND 2.                 
C              SF - SCALE FACTOR AT THE CENTRAL MERIDIAN.                       
C                                                                               
C        OUTPUT:                                                                
C                                                                               
C              TT - T-T CORRECTION FROM POINT 1 TO 2.                           
C              LS - LINE SCALE FOR THE DISTANCE FROM 1 TO 2.                    
C                                                                               
C                                           WRITTEN BY G.BOWIE, NOV. 1977.      
C                                                                               
      IMPLICIT REAL*8(A-Z)                                                      
      PI=3.141592653589793D0                                                    
      X1=X1-XO                                                                  
      X2=X2-XO                                                                  
      CP=DCOS(PHI1)                                                             
      SP=DSIN(PHI1)                                                             
      E=DSQRT((A**2-B**2)/A**2)                                                 
      DN=A/DSQRT(1.0D0-E**2*SP**2)                                              
      DM=A*(1.0D0-E**2)/DSQRT((1.0D0-E**2*SP**2)**3)                            
      N1=DSQRT(DM*DN)                                                           
      DEN=6.D0*(N1**2)                                                          
      TT=(Y2-Y1)*(X2+2*X1)/DEN                                                  
      LS= 1.D0+(X1**2+X1*X2+X2**2)/DEN                                          
      LS=LS*SF                                                                  
      X1=X1+XO                                                                  
      X2=X2+XO                                                                  
      RETURN                                                                    
      END