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sample1d(1)                           GMT                          sample1d(1)




NAME

       sample1d - Resample 1-D table data using splines


SYNOPSIS

       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.


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  decreas-
       ing)  variable, here called time (it may of course be any type of quan-
       tity).  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 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.

       -Af|p|m|r|R
              For track resampling (if -Ta|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 nec-
              essarily 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 neces-
              sarily 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_INTER-
              POLANT  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 sam-
              pling 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 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.

       -Sstart[stop]
              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 a|)
              Select verbosity level [c].

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

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

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

       -e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
              Only accept data records that match the given pattern.

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

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

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

       -icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
              Select input columns and transformations (0 is first column).

       -ocols[,a|] (more a|)
              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 explana-
              tion 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.


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 aFlat Eartha 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,  absolute  time  is  under  the  control  of  FOR-
       MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point  val-
       ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for-
       mat 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 set-
       ting.


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,dis-
       tance,gravity,magnetics,bathymetry) records, at 1km equidistant  inter-
       vals using Akimaas 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(1), gmt.conf(5), greenspline(1), filter1d(1)


COPYRIGHT

       2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe



5.4.2                            Jun 24, 2017                      sample1d(1)

gmt5 5.4.2 - Generated Thu Jun 29 16:17:34 CDT 2017
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