*-- Author : S.Burke
      SUBROUTINE FKETOI(EXT,SINT,CINT)
**********************************************************************                                        
*                                                                    *                                        
* Convert an `external' state vector to an `internal' vector         *                                        
* and covariance.                                                    *                                        
*                                                                    *                                        
* External: 1/r, phi, theta, x, y, z, IPTYPE, covariance             *                                        
* Internal: x, y, q/p, tan(theta), phi                               *                                        
*                                                                    *                                        
* The `external' covariance is packed with COVCP.                    *                                        
*                                                                    *                                        
**********************************************************************                                        
*KEEP,FKPIDP.                                                                                                 
*KEND.                                                                                                        
**********************************************************************                                        
* Get the field                                                                                               
      CALL GUFLD(EXT(4),B)                                                                             
* Trap zero field problems                                                                                    
* Transform the state vector                                                                                  
* Trap more zero-field problems                                                                               
* Differential coefficients                                                                                   
* Unpack the covariance ...                                                                                   
      CALL COVCP(5,COV,EXT(8),2)                                                                       
* ... and transform it                                                                                        
* Trap more zero-field problems                                                                               
*