## 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, with Equator as y = 0)
               -Jtlon0/lat0/scale (TM - Transverse Mercator, set origin)
               -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 (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 (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].  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