grdvector compx.nc compy.nc -Jparameters [ -A ] [ -B[p|s]parameters ] [ -Gfill ] [ -Ixinc[unit][=|+][/yinc[unit][=|+]] ] [ -K ] [ -N ] [ -O ] [ -P ] [ -Qparameters ] [ -R[unit]xmin/xmax/ymin/ymax[r] ] [ -S[i|l]scale ] [ -T ] [ -U[just/dx/dy/][c|label] ] [ -Wpen ] [ -X[a|c|f|r][x-shift[u]] ] [ -Y[a|c|f|r][y-shift[u]] ] [ -Z ] [ -ccopies ] [ -f[i|o]colinfo ] [ -p[x|y|z]azim/elev[/zlevel][+wlon0/lat0[/z0]][+vx0/y0] ] [ -t[transp] ] 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 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. 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. When reading grids, the format is generally automatically recognized. If not, the same suffix can be added to input grid file names. See grdreformat and Section Grid file format specifications 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 grdreformat and Section Grid file format specifications of the GMT Technical Reference and Cookbook for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids. 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: +g-|fill turns off vector head fill (if -) or sets the vector head fill [Default fill is used, which may be no fill]. +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 is instead the start and stop opening angles of the arc segment relative to the point. +jjust determines how the input x,y point relates to the vector. Choose from beginning [default], end, or center. 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 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, try Source.