xenial (1) grdvector.1gmt.gz

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NAME

       grdvector - Plot vector field from two component grids

SYNOPSIS

       grdvector  compx.nc compy.nc -Jparameters [  ] [ [p|s]parameters ] [ cpt ] [ fill ] [ [x]dx[/dy] ] [  ] [
       ] [  ] [  ] [ parameters ] [ region ] [ [i|l]scale ] [  ] [ [just/dx/dy/][c|label] ] [ pen ] [ x_offset ]
       [ y_offset ] [  ] [ -ccopies ] [ -f<flags> ] [ -p<flags> ] [ -t<transp> ]

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

DESCRIPTION

       grdvector  reads  two  2-D  grid  files  which  represents  the x- and y-components of a vector field and
       produces a vector field plot by drawing vectors with orientation and length according to the  information
       in the files. Alternatively, polar coordinate r, theta grids may be given instead.

REQUIRED ARGUMENTS

       compx.nc
              Contains the x-components of the vector field.

       compy.nc
              Contains the y-components of the vector field. (See GRID FILE FORMATS below.)

       -Jparameters (more ...)
              Select map projection.

OPTIONAL ARGUMENTS

       -A     The  grid  files  contain  polar  (r,  theta)  components  instead of Cartesian (x, y) [Default is
              Cartesian components].

       -B[p|s]parameters (more ...)
              Set map boundary intervals.

       -C[cpt]
              Use cpt to assign colors based on vector length. Alternatively, supply the name  of  a  GMT  color
              master  CPT [rainbow] and let grdvector automatically determine a 16-level continuous CPT from the
              grid's z-range.  Yet another option is to specify -Ccolor1,color2[,color3,...]  to build a  linear
              continuous  cpt  from  those  colors automatically.  In this case colorn can be a r/g/b triplet, a
              color name, or an HTML hexadecimal color (e.g. #aabbcc ).

       -Gfill Sets color or shade for vector interiors [Default is no fill].

       -I[x]dx[/dy]
              Only plot vectors at nodes every x_inc, y_inc apart (must be multiples of original grid  spacing).
              Append  m  for  arc minutes or s for arc seconds.  Alternatively, use -Ix to specify the multiples
              multx[/multy] directly [Default plots every node].

       -K (more ...)
              Do not finalize the PostScript plot.

       -N     Do NOT clip vectors at map boundaries [Default will clip].

       -O (more ...)
              Append to existing PostScript plot.

       -P (more ...)
              Select "Portrait" plot orientation.

       -Qparameters
              Modify vector parameters. For  vector  heads,  append  vector  head  size  [Default  is  0,  i.e.,
              stick-plot]. See VECTOR ATTRIBUTES for specifying additional attributes.

       -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
              Specify the region of interest. Specify a subset of the grid.

       -S[i|l]scale
              Sets  scale for Cartesian vector length in data units per distance measurement unit [1]. Append c,
              i, or p to indicate the measurement unit (cm, inch,or point). Prepend l to indicate a fixed length
              for  all  vectors.  For Geographic data, give scale in data units per km. Use -Si if it is simpler
              to give the reciprocal scale in measurement unit per data unit or km per data unit.

       -T     Means the azimuths of Cartesian data sets should be adjusted according to the signs of the  scales
              in  the  x- and y-directions [Leave alone].  This option can be used to convert vector azimuths in
              cases when a negative scale is used in one of both directions (e.g., positive down).

       -U[just/dx/dy/][c|label] (more ...)
              Draw GMT time stamp logo on plot.

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

       -Wpen  Set pen attributes used for vector outlines [Default: width = default,  color  =  black,  style  =
              solid].

       -X[a|c|f|r][x-shift[u]]

       -Y[a|c|f|r][y-shift[u]] (more ...)
              Shift plot origin.

       -Z     The theta grid provided contains azimuths rather than directions (requires -A).

       -ccopies (more ...)
              Specify number of plot copies [Default is 1].

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

       -p[x|y|z]azim/elev[/zlevel][+wlon0/lat0[/z0]][+vx0/y0] (more ...)
              Select perspective view.

       -t[transp] (more ...)
              Set PDF transparency level in percent.

       -^ 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.

GRID FILE FORMATS

       By default GMT writes out grid as single precision floats  in  a  COARDS-complaint  netCDF  file  format.
       However,  GMT  is  able  to  produce  grid  files  in many other commonly used grid file formats and also
       facilitates so called "packing" of grids, writing out floating point data as 1- or  2-byte  integers.  To
       specify  the  precision, scale and offset, the user should add the suffix =id[/scale/offset[/nan]], where
       id is a two-letter identifier of the grid type and precision, and scale and  offset  are  optional  scale
       factor  and  offset to be applied to all grid values, and nan is the value used to indicate missing data.
       In case the two characters id is not provided, as in =/scale than  a  id=nf  is  assumed.   When  reading
       grids,  the  format  is generally automatically recognized. If not, the same suffix can be added to input
       grid file names. See grdconvert and Section grid-file-format of the GMT Technical Reference and  Cookbook
       for more information.

       When  reading  a  netCDF  file  that  contains  multiple  grids,  GMT  will  read,  by default, the first
       2-dimensional grid that can find in that  file.  To  coax  GMT  into  reading  another  multi-dimensional
       variable  in  the grid file, append ?varname to the file name, where varname is the name of the variable.
       Note that you may need to escape the special meaning of ? in your shell program by putting a backslash in
       front  of  it, or by placing the filename and suffix between quotes or double quotes. The ?varname suffix
       can also be used for output grids to specify a  variable  name  different  from  the  default:  "z".  See
       grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical Reference and Cookbook
       for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.

VECTOR ATTRIBUTES

       Several modifiers may be appended to the vector-producing options to  specify  the  placement  of  vector
       heads, their shapes, and the justification of the vector. Below, left and right refers to the side of the
       vector line when viewed from the start point to the end point of the segment:
          +aangle sets the angle of the vector head apex [30].

          +b places a vector head at the beginning of the vector  path  [none].   Optionally,  append  t  for  a
          terminal  line, c for a circle, or a for arrow [Default].  Further append l|r to only draw the left or
          right side of this head [both sides].

          +e places a vector head at the end of the vector path [none].  Optionally, append  t  for  a  terminal
          line,  c  for  a  circle, or a for arrow [Default].  Further append l|r to only draw the left or right
          side of this head [both sides].

          +g-|fill turns off vector head fill (if -) or sets the vector head fill [Default fill is  used,  which
          may be no fill].

          +l draws half-arrows, using only the left side of specified heads [both sides].

          +m places a vector head at the mid-point the vector path [none].  Append f or r for forward or reverse
          direction of the vector [forward].  Optionally, append t for a terminal line, c for a circle, or a for
          arrow  head  [Default].   Further  append  l|r  to only draw the left or right side of this head [both
          sides].  Cannot be combined with +b or +e.

          +nnorm scales down vector attributes (pen thickness, head size) with decreasing length, where  vectors
          shorter than norm will have their attributes scaled by length/norm [arrow attributes remains invariant
          to length].

          +oplon/plat specifies the oblique pole for the great or small circles.  Only needed for great  circles
          if +q is given.

          +p[-][pen]  sets the vector pen attributes. If pen has a leading - then the head outline is not drawn.
          [Default pen is used, and head outline is drawn]

          +q means the input angle, length data instead represent the start and stop opening angles of  the  arc
          segment relative to the given point.

          +r draws half-arrows, using only the right side of specified heads [both sides].

          t[b|e]trim will shift the beginning or end point (or both) along the vector segment by the given trim;
          append suitable unit. If the modifiers b|e are not used then trim may be two  values  separated  by  a
          slash,  which  is  used  to specify different trims for the two ends.  Positive trims will shorted the
          vector while negative trims will lengthen it [no trim].

       In addition, all but circular vectors may take these modifiers:
          +jjust determines how the input x,y point relates to the vector. Choose from beginning [default], end,
          or center.

          +s means the input angle, length is instead the x, y coordinates of the vector end point.

       Finally, Cartesian vectors may take these modifiers:
          +zscale[unit] expects input dx,dy vector components and uses the scale to convert to polar coordinates
          with length in given unit.

EXAMPLES

       To draw the vector field given by the files r.nc and theta.nc on a linear plot with scale 5 cm  per  data
       unit,  using  vector  rather  than stick plot, scale vector magnitudes so that 10 units equal 1 inch, and
       center vectors on the node locations, run

              gmt grdvector r.nc theta.nc -Jx5c -A -Q0.1i+e+jc -S10i > gradient.ps

       To plot a geographic data sets given the files com_x.nc and comp_y.nc, using a scale of 200 km  per  data
       unit and only plot every 3rd node in either direction, try

              gmt grdvector comp_x.nc comp_y.nc -Ix3 -JH0/20c -Q0.1i+e+jc -S200 > globe.ps

SEE ALSO

       gmt, gmtcolors, grdcontour, psxy

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