NAME

     grdvector - Plot vector fields from grdfiles


SYNOPSIS

     grdvector compx.grd compy.grd -Jparameters [ -A ] [  -Btick-
     info    ]   [   -Ccptfile   ]   [   -E   ]   [   -Gfill]   [
     -Ix_inc[m|c][/y_inc[m|c]] ] [ -K ] [ -N ] [ -O ] [  -P  ]  [
     -Qparameters  ] [ -Rwest/east/south/north[r] ] [ -Sscale ] [
     -T ] [ -U[/dx/dy/][label] ] [ -V ] [ -Wcontourpen ]  [  -Xx-
     shift ] [ -Yy-shift ] [ -Zzlevel ] [ -ccopies ]


DESCRIPTION

     grdvector reads two 2-D gridded 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 components may be used (r, theta).  grdvec-
     tor  is  basically a short-hand for using 2 calls to grd2xyz
     and pasting the output through psxy -SV.

     compx.grd
          Contains the x-component of the vector field.

     compy.grd
          Contains the y-component of the vector field.

     -J   Selects  the  map  projection.  Scale  is  UNIT/degree,
          1:xxxxx,  or width in UNIT (upper case modifier).  UNIT
          is cm, inch, or m, depending on the  MEASURE_UNIT  set-
          ting in .gmtdefaults, but this can be overridden on the
          command line by  appending  the  c,  i,  or  m  to  the
          scale/width value.

          CYLINDRICAL PROJECTIONS:

          -Jclon0/lat0/scale (Cassini)
          -Jjlon0/scale (Miller)
          -Jmscale (Mercator - Greenwich and Equator as origin)
          -Jmlon0/lat0/scale (Mercator - Give meridian and  stan-
          dard parallel)
          -Joalon0/lat0/azimuth/scale (Oblique Mercator  -  point
          and azimuth)
          -Joblon0/lat0/lon1/lat1/scale (Oblique Mercator  -  two
          points)
          -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point
          and pole)
          -Jqlon0/scale   (Equidistant   Cylindrical   Projection
          (Plate Carree))
          -Jtlon0/scale (TM - Transverse Mercator,  with  Equator
          as y = 0)
          -Jtlon0/lat0/scale (TM - Transverse Mercator, set  ori-
          gin)
          -Juzone/scale (UTM - Universal Transverse Mercator)
          -Jylon0/lats/scale (Basic Cylindrical Projection)

          AZIMUTHAL PROJECTIONS:

          -Jalon0/lat0/scale (Lambert).
          -Jelon0/lat0/scale (Equidistant).
          -Jflon0/lat0/horizon/scale (Gnomonic).
          -Jglon0/lat0/scale (Orthographic).
          -Jslon0/lat0/scale (General Stereographic)

          CONIC PROJECTIONS:

          -Jblon0/lat0/lat1/lat2/scale (Albers)
          -Jdlon0/lat0/lat1/lat2/scale (Equidistant)
          -Jllon0/lat0/lat1/lat2/scale (Lambert)

          MISCELLANEOUS PROJECTIONS:

          -Jhlon0/scale (Hammer)
          -Jilon0/scale (Sinusoidal)
          -Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
          -Jnlon0/scale (Robinson)
          -Jrlon0/scale (Winkel Tripel)
          -Jvlon0/scale (Van der Grinten)
          -Jwlon0/scale (Mollweide)

          NON-GEOGRAPHICAL PROJECTIONS:

          -Jpscale[/origin] (polar (theta,r) coordinates, option-
          ally offset theta [0])
          -Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log,  and
          power scaling)
          More details can be found in the psbasemap manpages.


OPTIONS

     No space between the option flag and  the  associated  argu-
     ments.

     -A   Means grdfiles have polar (r, theta) components instead
          of Cartesian (x, y).

     -B   Sets map boundary tickmark intervals. See psbasemap for
          details.

     -C   Use cptfile to assign colors based on vector length.

     -E   Center vectors on grid nodes [Default draws  from  grid
          node].

     -G   Sets color or shade for vector interiors [Default is no
          fill].   Specify the shade (0-255) or color (r/g/b), or
          -Gpdpi/pattern, where pattern gives the number  of  the
          built-in pattern (1-90) OR the name of a Sun 1-, 8-, or
          24-bit raster file.  dpi sets  the  resolution  of  the
          image.   For  1-bit rasters: use -GP for inverse video,
          or append :Fr/g/b[B[r/g/b]] to specify fore- and  back-
          ground  colors  (use  r/g/b = - for transparency).  See
          GMT Cookbook  &  Technical  Reference  Appendix  E  for
          information on individual patterns.

     -I   Only plot vectors at nodes  every  x_inc,  y_inc  apart
          (must be multiples of original grid spacing).  Append m
          for minutes or c  for  seconds.  [Default  plots  every
          node].

     -K   More PostScript code will be  appended  later  [Default
          terminates the plot system].

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

     -O   Selects Overlay plot mode [Default  initializes  a  new
          plot system].

     -P   Selects  Portrait  plotting  mode   [GMT   Default   is
          Landscape, see gmtdefaults to change this].

     -Q   Select vector plot [Default  is  stick-plot].   Option-
          ally,       specify      parameters      which      are
          arrowwidth/headlength/headwidth       [Default       is
          0.075c/0.3c/0.25c (or 0.03i/0.12i/0.1i)].  Append nsize
          which will cause vectors  shorter  than  size  to  have
          their appearence scaled by length/size.

     -R   west, east, south, and  north  specify  the  Region  of
          interest.  To specify boundaries in degrees and minutes
          [and seconds], use the dd:mm[:ss] format.  Append r  if
          lower  left  and  upper right map coordinates are given
          instead of wesn.  Specify a subset of the grid.

     -S   Sets scale for vector length in data units per distance
          measurement unit [1].

     -T   Means azimuth should be converted to  angles  based  on
          the selected map projection.

     -U   Draw Unix System time stamp on plot.  User may  specify
          where the lower left corner of the stamp should fall on
          the  page  relative  to  lower  left  corner  of  plot.
          Optionally,  append  a label, or c (which will plot the
          command string.)

     -V   Selects verbose mode, which will send progress  reports
          to stderr [Default runs "silently"].

     -W   Set pen attributes used for vector  outlines  [Default:
          width = 1, color = 0/0/0, texture = solid].

     -X -Y
          Shift origin of plot by (x-shift,y-shift).   Prepend  a
          for  absolute  coordinates;  the default (r) will reset
          plot origin.

     -Z   Means the angles  provided  are  azimuths  rather  than
          direction (requires -A).

     -c   Specifies the number of plot copies. [Default is 1]


EXAMPLES

     To draw the vector  field  given  by  the  files  r.grd  and
     theta.grd  on  a  linear plot with scale 5 cm per data unit,
     using vector rather than stick plot, and scale vector magni-
     tudes so that 10 units equal 1 inch, try

     grdvector r.grd theta.grd -Jx5c -Q -S0.1i > gradient.ps



SEE ALSO

     gmt(l), grdcontour(l), psxy(l)