NAME

     X_SOLVE_DC_DRIFT - Find Best-fitting  D.C.-shift  and  Drift
     Estimates


SYNOPSIS

     x_solve_dc_drift [ -Xxbase ] [ -Llbase ] [ -Iignorefile ]  [
     -S  ] [ -Citeration ] [ -Mmin_nx ] [ -Rwest/east/south/north
     ] [ -Uuselegsfile ] [ -V ] [ -Bbinfile ]  [ -AASCIIfile ]


DESCRIPTION

     x_solve_dc_drift  will  read  the  database  files  and,  by
     iterating,  find  the  best-fitting  regression  line to the
     <time,COE> points for each leg that  minimizes  the  overall
     standard deviation of the data set in a least squares sense.
     Finally, correction file(s) are created.

     -X   Indicate an alternate database  to  read.  [Default  is
          xx_base.b].

     -L   Indicate an alternate  legbase  to  read.  [Default  is
          xx_legs.b].

     -I   Ignore information for certain legs (that might be  bad
          etc).

     -S   Reset the old d.c.-shift and drift  estimates  to  zero
          before iterating.

     -C   Specify how many iterations to do. Default is  interac-
          tive session.

     -M   Solve for drift only if the leg has  more  than  min_nx
          cross-overs.

     -R   Only  take  COEs  inside  this  region  into   account.
          [Default is world].

     -U   Solve for corrections involving COEs from legs  in  the
          uselegsfile only.

     -B   Create a binary correction file (which can be  read  by
          xlist and gmtlist).

     -A   Create an ASCII correction table. At least  one  of  -A
          and -B must be specified.

     -V   Operate in verbose mode.


     The reason for the -M option is that if the  COEs  are  few,
     then  a  stable  estimate  of  the slope may not be obtained
     (e.g. when most of the COEs  occur  midway  between  ports).
     However,  in  most  cases the bulk of the COEs do occur near
     the ports so that a drift estimate can be computed.  Conven-
     tional  wisdom  recommends  plotting the time-series and the
     computed regression line to see if it makes sense.


SEE ALSO

     gmt(l), x_system(l)


REFERENCES

     Wessel, P. XOVER: A  Cross-over  Error  Detector  for  Track
     Data, Computers & Geosciences, 15, 333-346.