x2sys_solve(1) GMT x2sys_solve(1)
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 follow-
ing 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 a|)
Select verbosity level [c].
-W Means that each input records has an extra column with the com-
posite 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 a|)
Select native binary input.
-dinodata (more a|)
Replace input columns that equal nodata with NaN.
-x[[-]n] (more a|)
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 explana-
tion 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 particu-
lar 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(1), x2sys_cross(1), x2sys_datalist(1), x2sys_get(1),
x2sys_init(1), x2sys_list(1), x2sys_put(1), x2sys_report(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 x2sys_solve(1)
gmt5 5.4.2 - Generated Thu Jun 29 18:26:32 CDT 2017