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SAMPLE1D(1)                  Generic Mapping Tools                 SAMPLE1D(1)

NAME
       sample1d - Resampling of 1-D data sets

SYNOPSIS
       sample1d 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] ]

DESCRIPTION
       sample1d 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
       number of the independent (monotonically increasing or decreasing)
       variable.  Equidistant or arbitrary sampling can be selected.  All
       columns are resampled based on the new sampling interval.  Several
       interpolation 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
              monotonically 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
              geographical 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
              (absolute 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
       precision, 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
       current TIME_UNIT units.  There is not yet support for variable
       intervals such as months.

EXAMPLES
       To resample the file profiles.tdgmb, which contains
       (time,distance,gravity,magnetics,bathymetry) records, at 1km
       equidistant intervals 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 ALSO
       GMT(1), filter1d(1)

GMT 4.5.14                        1 Nov 2015                       SAMPLE1D(1)