Provided by: gmt-common_5.4.3+dfsg-1_all bug


       sample1d - Resample 1-D table data using splines


       sample1d  [  table  ]  [   -Af|p|m|r|R[+l]  ]  [   -Fl|a|c|n[+1|+2]  ]  [  -Iinc[unit] ] [
       -Nknotfile ] [  -Sstart[/stop] ] [  -Tcol ] [  -V[level] ] [ -bbinary ]  [  -dnodata  ]  [
       -eregexp ] [ -fflags ] [ -ggaps ] [ -hheaders ] [ -iflags ] [ -oflags ]

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


       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, here called time (it may of  course  be  any  type  of
       quantity).   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.




       table  This is one or more ASCII [of binary, see -bi] files with one column containing the
              independent time 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.

              For track resampling (if -Tunit 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).

              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,

              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

              knotfile is an optional ASCII file with the time 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.

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

       -e[~]”pattern” | -e[~]/regexp/[i] (more …)
              Only accept data records that match the given pattern.

       -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 and transformations (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
              just use -).

       -+ 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 all options,
              then exits.


       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).


       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, absolute  time  is
       under  the control of FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
       lead  to loss of precision in ASCII 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.


       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.


       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


       gmt, gmt.conf, greenspline, filter1d


       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe