NAME

       x2sys_solve - Determine least-squares systematic correction from crossovers

SYNOPSIS

       x2sys_solve  -Ccolumn  -TTAG  -Emode [ COE_list.d ] [  -V[level] ] [  -W[u] ] [ -bibinary ] [ -dinodata ]
       [ -x[[-]n] ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       x2sys_solve will use the supplied crossover information to solve for systematic corrections that can then
       be  applied  per  track to improve data quality. Several systematic corrections can be solved for using a
       least-squares approach. Note: Only one data column can be processed at the time.

REQUIRED ARGUMENTS

       COE_list.d
              Name of file with the required crossover columns as produced by x2sys_list. NOTE: If -bi  is  used
              then  the  first two columns are expected to hold the integer track IDs; otherwise we expect those
              columns to hold the text string names of the two tracks. If no file is given  we  will  read  from
              stdin.

       -TTAG  Specify the x2sys TAG which tracks the attributes of this data type.

       -Ccolumn
              Specify  which  data  column  you  want  to  process.  Needed  for proper formatting of the output
              correction table and must match the same option used in x2sys_list when preparing the input data.

       -Emode The correction type you wish to model. Choose among the following functions f(p) , where p are the
              m parameters per track that we will fit simultaneously using a least squares approach:

              c will fit f(p) = a (a constant offset); records must contain track ID1, ID2, COE.

              d will fit f(p) = a + b * d (linear drift; d is distance; records must contain track ID1, ID2, d1,
              d2, COE.

              g will fit f(p) = a + b sin(y)^2 (1980-1930 gravity correction); records must contain  track  ID1,
              ID2, latitude y, COE.

              h  will  fit f(p) = a + b cos(H) + c cos(2H) + d sin(H) + e sin(2H) (magnetic heading correction);
              records must contain track ID1, ID2, heading H, COE.

              s will fit f(p) = a * z (a unit scale correction); records must contain track ID1, ID2, z1, z2.

              t will fit f(p) = a + b * (t - t0) (linear drift; t0 is the start time of the track); records must
              contain track ID1, ID2, t1-t0, t2-t0, COE.

OPTIONAL ARGUMENTS

       -V[level] (more …)
              Select verbosity level [c].

       -W     Means that each input records has an extra column with the composite  weight  for  each  crossover
              record.  These  are  used  to  obtain  a weighted least squares solution [no weights]. Append u to
              report unweighted mean/std [Default, report weighted stats].

       -bi[ncols][t] (more …)
              Select native binary input.

       -dinodata (more …)
              Replace input columns that equal nodata with NaN.

       -x[[-]n] (more …)
              Limit number of cores used in multi-threaded algorithms (OpenMP required).

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows just use -).

       -+ or just +
              Print an extensive usage (help) message, including the explanation of any  module-specific  option
              (but not the GMT common options), then exits.

       -? or no arguments
              Print a complete usage (help) message, including the explanation of all options, then exits.

NOTES

       Most  of  the  model  corrections  in   -E involve a constant offset.  Because crossovers are differences
       between values, any absolute level will cancel out and hence the constant offsets we obtain are  relative
       to  an  undetermined absolute level.  To obtain a solvable solution we add the constraint that the sum of
       all constant offsets equal zero.  If the tracks form clusters in which no tracks from one  cluster  cross
       any  track  from another cluster then these are two independent data sets and require they own constraint
       equation for their offsets.  We determine the number of  clusters  and  automatically  add  the  required
       constraint  equations.   If  you  need a particular reference track to have a particular offset (e.g., 0)
       then you can subtract the offset you found from every track correction and add in the desired offset.

EXAMPLES

       To fit a simple bias offset to faa for all tracks under the MGD77 tag, try

              gmt x2sys_list COE_data.txt -V -TMGD77 -Cfaa -Fnc > faa_coe.txt
              gmt x2sys_solve faa_coe.txt -V -TMGD77 -Cfaa -Ec > coe_table.txt

       To fit a faa linear drift with time instead, try

              gmt x2sys_list COE_data.txt -V -TMGD77 -Cfaa -FnTc > faa_coe.txt
              gmt x2sys_solve faa_coe.txt -V -TMGD77 -Cfaa -Et > coe_table.txt

       To estimate heading corrections based on magnetic crossovers associated with the tag MGD77 from the  file
       COE_data.txt, try

              gmt x2sys_list COE_data.txt -V -TMGD77 -Cmag -Fnhc > mag_coe.txt
              gmt x2sys_solve mag_coe.txt -V -TMGD77 -Cmag -Eh > coe_table.txt

       To estimate unit scale corrections based on bathymetry crossovers, try

              gmt x2sys_list COE_data.txt -V -TMGD77 -Cdepth -Fnz > depth_coe.txt
              gmt x2sys_solve depth_coe.txt -V -TMGD77 -Cdepth -Es > coe_table.txt

SEE ALSO

       x2sys_binlist, x2sys_cross, x2sys_datalist, x2sys_get, x2sys_init, x2sys_list, x2sys_put, x2sys_report

COPYRIGHT

       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe

5.4.3                                             Jan 03, 2018                                 X2SYS_SOLVE(1gmt)