xenial (1) sample1d.1gmt.gz

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