NAME

       sample1d - Resample 1-D table data using splines

SYNOPSIS

       sample1d  [  table  ]  [  f|p|m|r|R[+l]  ] [ l|a|c|n[+1|+2] ] [ inc[unit] ] [ knotfile ] [
       start[/stop] ] [ col ] [ [level] ] [ -b<binary> ] [ -d<nodata> ] [ -f<flags> ] [  -g<gaps>
       ] [ -h<headers> ] [ -i<flags> ] [ -o<flags> ]

       Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

       sample1d reads a multi-column ASCII [or binary] data set from file [or standard input] and
       interpolates the time-series or spatial 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.

REQUIRED ARGUMENTS

       None.

OPTIONAL ARGUMENTS

       table  This is one or more ASCII [of binary, see -bi] files with one column containing the
              independent variable (which must be monotonically in/de-creasing) and the remaining
              columns holding other data values. If no file  is  provided,  sample1d  reads  from
              standard input.

       -Af|p|m|r|R
              For  track  resampling  (if  -T...unit  is  set)  we  can  select how this is to be
              performed. Append f to keep original points, but add intermediate points if needed;
              note  this  selection does not necessarily yield equidistant points [Default], m as
              f, but first follow meridian (along y) then parallel (along x), p as f,  but  first
              follow  parallel  (along  y)  then meridian (along x), r to resample at equidistant
              locations; input points are not necessarily included in the output, and R as r, but
              adjust  given  spacing  to  fit  the  track  length  exactly. Finally, append +l if
              distances should be measured along rhumb lines (loxodromes).

       -Fl|a|c|n[+1|+2]
              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  GMT_INTERPOLANT  in  your  gmt.conf  file.   You  may  optionally
              evaluate  the  first  or  second  derivative  of  the  spline  by appending 1 or 2,
              respectively.

       -Iinc[unit]
              inc defines the sampling interval [Default is the separation between the first  and
              second abscissa point in the table]. Append a distance unit (see UNITS) to indicate
              that the first two columns contain longitude, latitude and  you  wish  to  resample
              this  path  with  a  spacing  of  inc  in  the chosen units. For sampling of (x, y)
              Cartesian tracks, specify the unit as c. Use -A to control how path  resampling  is
              performed.

       -Nknotfile
              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 table and
              knotfile.  Also note that -i never applies to knotfile since we always consider the
              first column only.

       -Sstart[stop]
              For equidistant sampling, start indicates the location of the first  output  value.
              [Default  is  the  smallest  even  multiple  of  inc  inside  the  range of table].
              Optionally, append /stop to indicate the location of the last output value [Default
              is the largest even multiple of inc inside the range of table].

       -Tcol  Sets the column number of the independent variable [Default is 0 (first)].

       -V[level] (more ...)
              Select verbosity level [c].

       -bi[ncols][t] (more ...)
              Select  native  binary  input.  [Default  is  2  (or at least the number of columns
              implied by -T)].

       -bo[ncols][type] (more ...)
              Select native binary output. [Default is same as input].

       -d[i|o]nodata (more ...)
              Replace input columns that equal nodata with NaN and do the reverse on output.

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (more ...)
              Determine data gaps and line breaks.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
              Skip or produce header record(s).

       -icols[l][sscale][ooffset][,...] (more ...)
              Select input columns (0 is first column).

       -ocols[,...] (more ...)
              Select output columns (0 is first column).

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              use just -).

       -+ 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  options,  then
              exits.

       --version
              Print GMT version and exit.

       --show-datadir
              Print full path to GMT share directory and exit.

UNITS

       For  map  distance  unit,  append  unit  d for arc degree, m for arc minute, and s for arc
       second, or e for meter [Default], f for foot, k for km, M for statute mile, n for nautical
       mile,  and  u  for  US survey foot. By default we compute such distances using a spherical
       approximation with great circles. Prepend - to a distance (or the unit is no  distance  is
       given)  to  perform  "Flat Earth" calculations (quicker but less accurate) or prepend + to
       perform exact geodesic calculations (slower but more accurate).

ASCII FORMAT PRECISION

       The ASCII output formats of numerical data are controlled by parameters in  your  gmt.conf
       file.  Longitude  and  latitude  are  formatted according to FORMAT_GEO_OUT, whereas other
       values are formatted according to FORMAT_FLOAT_OUT. 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 FORMAT_FLOAT_OUT 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

              gmt sample1d profiles.tdgmb -I1 -Fa -T1 > 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

              gmt sample1d depths.dt -Ngrav_pos.dg -Fc > new_depths.dt

       To resample the file points.txt every  0.01  from  0-6,  using  a  cubic  spline  for  the
       interpolation, but output the first derivative instead (the slope), try

              gmt sample1d points.txt S0/6 -I0.01 -Fc+1 > slopes.txt

       To resample the file track.txt which contains lon, lat, depth every 2 nautical miles, use

              gmt sample1d track.txt -I2n -AR > new_track.dt

       To do approximately the same, but make sure the original points are included, use

              gmt sample1d track.txt -I2n -Af > new_track.dt

       To obtain a rhumb line (loxodrome) sampled every 5 km instead, use

              gmt sample1d track.txt -I5k -AR+l > new_track.dt

SEE ALSO

       gmt, gmt.conf, greenspline, filter1d

COPYRIGHT

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe