NAME

      grdvector - Plot vector fields from grdfiles

SYNOPSIS

      grdvector compx.grd compy.grd -Jparameters [ -A ] [ -Btickinfo ] [
      -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).  grdvector 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 inch/degree, 1:xxxxx, or
           width in inch (upper case modifier).

           CYLINDRICAL PROJECTIONS:

           -Jclon0/lat0/scale (Cassini)
           -Jjlon0/scale (Miller)
           -Jmscale (Mercator - Greenwich and Equator as origin)
           -Jmlon0/lat0/scale (Mercator - Give meridian and standard
           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)
           -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)
           -Jllon0/lat0/lat1/lat2/scale (Lambert)

           MISCELLANEOUS PROJECTIONS:

           -Jhlon0/scale (Hammer)
           -Jilon0/scale (Sinusoidal)
           -Jklon0/scale (Eckert VI)
           -Jnlon0/scale (Robinson)
           -Jrlon0/scale (Winkel Tripel)
           -Jwlon0/scale (Mollweide)

           NON-GEOGRAPHICAL PROJECTIONS:

           -Jpscale (Linear projection for polar (theta,r) coordinates)
           -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 arguments.

      -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
           background colors.  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].  Optionally, specify
           parameters which are arrowwidth/headlength/headwidth (in inch)
           [Default is 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 inch [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 in inch [Default is (-0.75i/-
           0.75i)].  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) inch  [Default is
           (a1i,a1i) for new plots, (0,0) for overlays].  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 2 inch per data unit, using vector rather than
      stick plot, and scale vector magnitudes so that 10 units equal 1 inch,
      try

      grdvector r.grd theta.grd -Jx2i -Q -S0.1i > gradient.ps

SEE ALSO

      gmt, grdcontour, psxy