SAMPLE1D(1) Generic Mapping Tools SAMPLE1D(1)NAMEsample1d - Resampling of 1-D data sets
SYNOPSISsample1d infile [ -Fl|a|c|n ] [ -H[i][nrec] ] [ -Ixinc ] [ -Nknotfile ]
[ -Sxstart ] [ -Tx_col ] [ -V ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ]
[ -f[i|o]colinfo ] [ -m[i|o][flag] ]
DESCRIPTIONsample1d reads a multi-column ASCII [or binary] data set from file [or
standard input] and interpolates the timeseries/profile at locations
where the user needs the values. The user must provide the column num‐
ber of the independent (monotonically increasing or decreasing) vari‐
able. Equidistant or arbitrary sampling can be selected. All columns
are resampled based on the new sampling interval. Several interpola‐
tion schemes are available. Extrapolation outside the range of the
input data is not supported.
infile This is a multi-column ASCII [of binary, see -b] file with one
column containing the independent variable (which must be mono‐
tonically in/de-creasing) and the remaining columns holding
misc. data values. If no file is provided, sample1d reads from
standard input.
OPTIONS
No space between the option flag and the associated arguments.
-F Choose from l (Linear), a (Akima spline), c (natural cubic
spline), and n (no interpolation: nearest point) [Default is
-Fa]. You may change the default interpolant; see INTERPOLANT
in your .gmtdefaults4 file.
-H Input file(s) has header record(s). If used, the default number
of header records is N_HEADER_RECS. Use -Hi if only input data
should have header records [Default will write out header
records if the input data have them]. Blank lines and lines
starting with # are always skipped.
-I xinc defines the sampling interval. [Default is the separation
between the first and second abscissa point in the infile]
-N knotfile is an optional ASCII file with the x locations where
the data set will be resampled in the first column. Note: if -H
is selected it applies to both infile and knotfile.
-S For equidistant sampling, xstart indicates the location of the
first output value. [Default is the smallest even multiple of
xinc inside the range of infile]
-T Sets the column number of the independent variable [Default is 0
(first)].
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-bi Selects binary input. Append s for single precision [Default is
d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of columns in your binary
input file if it exceeds the columns needed by the program. Or
append c if the input file is netCDF. Optionally, append
var1/var2/... to specify the variables to be read. [Default is
2 (or at least the number of columns implied by -T)].
-bo Selects binary output. Append s for single precision [Default
is d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of desired columns in your
binary output file. [Default is same as input].
-f Special formatting of input and/or output columns (time or geo‐
graphical data). Specify i or o to make this apply only to
input or output [Default applies to both]. Give one or more
columns (or column ranges) separated by commas. Append T (abso‐
lute calendar time), t (relative time in chosen TIME_UNIT since
TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
to each column or column range item. Shorthand -f[i|o]g means
-f[i|o]0x,1y (geographic coordinates).
-m Multiple segment file(s). Segments are separated by a special
record. For ASCII files the first character must be flag
[Default is '>']. For binary files all fields must be NaN and
-b must set the number of output columns explicitly. By default
the -m setting applies to both input and output. Use -mi and
-mo to give separate settings to input and output.
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters
in your .gmtdefaults4 file. Longitude and latitude are formatted
according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
according to D_FORMAT. Be aware that the format in effect can lead to
loss of precision in the output, which can lead to various problems
downstream. If you find the output is not written with enough preci‐
sion, consider switching to binary output (-bo if available) or specify
more decimals using the D_FORMAT setting.
CALENDAR TIME SAMPLING
If the abscissa are calendar times then you must use the -f option to
indicate this. Furthermore, -I then expects an increment in the cur‐
rent TIME_UNIT units. There is not yet support for variable intervals
such as months.
EXAMPLES
To resample the file profiles.tdgmb, which contains (time,dis‐
tance,gravity,magnetics,bathymetry) records, at 1km equidistant inter‐
vals using Akima's spline, use
sample1d profiles.tdgmb -I 1 -Fa -T 1 > profiles_equi_d.tdgmb
To resample the file depths.dt at positions listed in the file
grav_pos.dg, using a cubic spline for the interpolation, use
sample1d depths.dt -N grav_pos.dg -Fc > new_depths.dt
SEE ALSOGMT(1), filter1d(1)GMT 4.5.14 1 Nov 2015 SAMPLE1D(1)
