1X2SYS_SOLVE(1) GMT X2SYS_SOLVE(1)
2
6 x2sys_solve - Determine least-squares systematic correction from
7 crossovers
8
10 x2sys_solve -Ccolumn -TTAG -Emode [ COE_list.d ] [ -V[level] ] [
11 -W[u] ] [ -bibinary ] [ -dinodata ] [ -x[[-]n] ]
12 Note: No space is allowed between the option flag and the associated
14 arguments.
15
17 x2sys_solve will use the supplied crossover information to solve for
18 systematic corrections that can then be applied per track to improve
19 data quality. Several systematic corrections can be solved for using a
20 least-squares approach. Note: Only one data column can be processed at
21 the time.
22
24 COE_list.d
25 Name of file with the required crossover columns as produced by
26 x2sys_list. NOTE: If -bi is used then the first two columns are
27 expected to hold the integer track IDs; otherwise we expect
28 those columns to hold the text string names of the two tracks.
29 If no file is given we will read from stdin.
30 -TTAG Specify the x2sys TAG which tracks the attributes of this data
32 type.
33 -Ccolumn
35 Specify which data column you want to process. Needed for proper
36 formatting of the output correction table and must match the
37 same option used in x2sys_list when preparing the input data.
38 -Emode The correction type you wish to model. Choose among the follow‐
40 ing functions f(p) , where p are the m parameters per track that
41 we will fit simultaneously using a least squares approach:
42 c will fit f(p) = a (a constant offset); records must contain
44 track ID1, ID2, COE.
45 d will fit f(p) = a + b * d (linear drift; d is distance;
47 records must contain track ID1, ID2, d1, d2, COE.
48 g will fit f(p) = a + b sin(y)^2 (1980-1930 gravity correction);
50 records must contain track ID1, ID2, latitude y, COE.
51 h will fit f(p) = a + b cos(H) + c cos(2H) + d sin(H) + e
53 sin(2H) (magnetic heading correction); records must contain
54 track ID1, ID2, heading H, COE.
55 s will fit f(p) = a * z (a unit scale correction); records must
57 contain track ID1, ID2, z1, z2.
58 t will fit f(p) = a + b * (t - t0) (linear drift; t0 is the
60 start time of the track); records must contain track ID1, ID2,
61 t1-t0, t2-t0, COE.
62
64 -V[level] (more ...)
65 Select verbosity level [c].
66 -W Means that each input records has an extra column with the com‐
68 posite weight for each crossover record. These are used to
69 obtain a weighted least squares solution [no weights]. Append u
70 to report unweighted mean/std [Default, report weighted stats].
71 -bi[ncols][t] (more ...)
73 Select native binary input.
74 -dinodata (more ...)
76 Replace input columns that equal nodata with NaN.
77 -x[[-]n] (more ...)
79 Limit number of cores used in multi-threaded algorithms (OpenMP
80 required).
81 -^ or just -
83 Print a short message about the syntax of the command, then
84 exits (NOTE: on Windows just use -).
85 -+ or just +
87 Print an extensive usage (help) message, including the explana‐
88 tion of any module-specific option (but not the GMT common
89 options), then exits.
90 -? or no arguments
92 Print a complete usage (help) message, including the explanation
93 of all options, then exits.
94
96 Most of the model corrections in -E involve a constant offset.
97 Because crossovers are differences between values, any absolute level
98 will cancel out and hence the constant offsets we obtain are relative
99 to an undetermined absolute level. To obtain a solvable solution we
100 add the constraint that the sum of all constant offsets equal zero. If
101 the tracks form clusters in which no tracks from one cluster cross any
102 track from another cluster then these are two independent data sets and
103 require they own constraint equation for their offsets. We determine
104 the number of clusters and automatically add the required constraint
105 equations. If you need a particular reference track to have a particu‐
106 lar offset (e.g., 0) then you can subtract the offset you found from
107 every track correction and add in the desired offset.
108
110 To fit a simple bias offset to faa for all tracks under the MGD77 tag,
111 try
112 gmt x2sys_list COE_data.txt -V -TMGD77 -Cfaa -Fnc > faa_coe.txt
114 gmt x2sys_solve faa_coe.txt -V -TMGD77 -Cfaa -Ec > coe_table.txt
115 To fit a faa linear drift with time instead, try
117 gmt x2sys_list COE_data.txt -V -TMGD77 -Cfaa -FnTc > faa_coe.txt
119 gmt x2sys_solve faa_coe.txt -V -TMGD77 -Cfaa -Et > coe_table.txt
120 To estimate heading corrections based on magnetic crossovers associated
122 with the tag MGD77 from the file COE_data.txt, try
123 gmt x2sys_list COE_data.txt -V -TMGD77 -Cmag -Fnhc > mag_coe.txt
125 gmt x2sys_solve mag_coe.txt -V -TMGD77 -Cmag -Eh > coe_table.txt
126 To estimate unit scale corrections based on bathymetry crossovers, try
128 gmt x2sys_list COE_data.txt -V -TMGD77 -Cdepth -Fnz > depth_coe.txt
130 gmt x2sys_solve depth_coe.txt -V -TMGD77 -Cdepth -Es > coe_table.txt
131
133 x2sys_binlist, x2sys_cross, x2sys_datalist, x2sys_get, x2sys_init,
134 x2sys_list, x2sys_put, x2sys_report
135
137 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1385.4.5 Feb 24, 2019 X2SYS_SOLVE(1)