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  interactive  ses-
              sion.

       -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 uselegs-
              file 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 esti-

       mate 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.  Conventional wisdom
       recommends plotting the time-series and the computed regression line to
       see if it makes sense.


SEE ALSO

       gmt(GMTMANSECTION), x_system(GMTMANSECTION)


REFERENCES

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



                                  1 Jan 2004               x_solve_dc_drift(l)

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