Provided by: gmt-common_5.4.5+dfsg-1_all

**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_solvewill 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.dName of file with the required crossover columns as produced by x2sys_list. NOTE: If-biis 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 fromstdin.-TTAGSpecify the x2sysTAGwhich tracks the attributes of this data type.-CcolumnSpecify 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.-EmodeThe correction type you wish to model. Choose among the following functions f(p) , wherepare themparameters per track that we will fit simultaneously using a least squares approach:cwill fit f(p) =a(a constant offset); records must contain track ID1, ID2, COE.dwill fit f(p) =a+b*d(linear drift;dis distance; records must contain track ID1, ID2, d1, d2, COE.gwill fit f(p) =a+bsin(y)^2 (1980-1930 gravity correction); records must contain track ID1, ID2, latitude y, COE.hwill fit f(p) =a+bcos(H) +ccos(2H) +dsin(H) +esin(2H) (magnetic heading correction); records must contain track ID1, ID2, heading H, COE.swill fit f(p) =a* z (a unit scale correction); records must contain track ID1, ID2, z1, z2.twill fit f(p) =a+b* (t-t0) (linear drift;t0is 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].-WMeans 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]. Appenduto report unweighted mean/std [Default, report weighted stats].-bi[ncols][t] (more ...) Select native binary input.-dinodata(more ...) Replace input columns that equalnodatawith 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-Einvolve 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**

2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe