x2sys_solve — GMT 5.1.1 documentation

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# x2sys_solve

x2sys_solve - Determine least-squares systematic correction from crossovers

## Synopsis

x2sys_solve -Ccolumn -TTAG -Emode [ COE_list.d ] [ -V[level] ] [ -W[u] ] [ -bi[ncols][type][w][+L|+B] ]

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 cruise ID1, ID2, COE.

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

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

  s will fit f(p) = a * z (a unit scale correction); records must contain cruise 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 cruise 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][type] (more ...)
  Select binary input.

-^
  Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
+
  Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.
-?
  Print a complete usage (help) message, including the explanation of options, then exits.
--version
  Print GMT version and exit.
--show-datadir
  Print full path to GMT share directory and exit.

## 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

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