*-- Author : S.Burke
      SUBROUTINE FKLFXY(SPRO,CPRO,WMES,CMES,SFIL,CFIL,CHISQ,IERR)
**********************************************************************                                        
*                                                                    *                                        
* Kalman Filter an x/y point                                         *                                        
*                                                                    *                                        
* ERROR CONDITIONS;                                                  *                                        
*       IERR =   0 ; normal termination                              *                                        
*   ->  IERR = 107 ; failure to invert measurement covariance        *                                        
*   ->  IERR = 111 ; failure to invert filtered covariance           *                                        
*       IERR =  12 ; covariance of filtered residuals n.p.d.         *                                        
*   ->  IERR = 116 ; x, y or theta has silly value                   *                                        
*       IERR =  17 ; tan(theta) > 1 (warning)                        *                                        
*                                                                    *                                        
*   ->  Fatal errors                                                 *                                        
*                                                                    *                                        
* NB Error 12 is not considered fatal, but the chi-sq will be zero   *                                        
*                                                                    *                                        
**********************************************************************                                        
*KEEP,FKECODE.                                                                                                
*KEND.                                                                                                        
**********************************************************************                                        
* Invert CMES                                                                                                 
         CALL FKERR(IUTIL,IROUT,IFATAL,IMCV,IERR)
* Compute the filtered (weighted average) covariance                                                          
      CALL FKCVXY(CPRO,GMES,CFIL,WT,IFAIL)
         CALL FKERR(IUTIL,IROUT,IFATAL,IOCV,IERR)
* Compute the filtered state vector                                                                           
      CALL FKWVEC(SPRO,WT,CFIL,GW,SFIL)
      CALL FKNORM(SFIL,IFAIL)
      IF (IFAIL.NE.0) CALL FKERR(IUTIL,IROUT,IFAIL/100,IFAIL,IERR)
* Calculate the chi**2                                                                                        
      CHISQ = FKCHXY(WMES,CMES,SFIL,CFIL,IFAIL)
      IF (IFAIL.NE.0) CALL FKERR(IUTIL,IROUT,IWARN,IFAIL,IERR)
*