<!-- Creator : groff version 1.19.2 --> <!-- CreationDate: Tue Mar 8 16:22:26 2011 --> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta name="generator" content="groff -Thtml, see www.gnu.org"> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <meta name="Content-Style" content="text/css"> <style type="text/css"> p { margin-top: 0; margin-bottom: 0; } pre { margin-top: 0; margin-bottom: 0; } table { margin-top: 0; margin-bottom: 0; } </style> <title>GRDVECTOR</title> </head> <body bgcolor="#ffffff"> <h1 align=center>GRDVECTOR</h1> <a href="#NAME">NAME</a><br> <a href="#SYNOPSIS">SYNOPSIS</a><br> <a href="#DESCRIPTION">DESCRIPTION</a><br> <a href="#OPTIONS">OPTIONS</a><br> <a href="#GRID FILE FORMATS">GRID FILE FORMATS</a><br> <a href="#EXAMPLES">EXAMPLES</a><br> <a href="#SEE ALSO">SEE ALSO</a><br> <hr> <a name="NAME"></a> <h2>NAME</h2> <p style="margin-left:11%; margin-top: 1em">grdvector − Plot vector fields from grid files</p> <a name="SYNOPSIS"></a> <h2>SYNOPSIS</h2> <p style="margin-left:11%; margin-top: 1em"><b>grdvector</b> <i>compx.grd compy.grd</i> <b>−J</b><i>parameters</i> [ <b>−A</b> ] [ <b>−B</b>[<b>p</b>|<b>s</b>]<i>parameters</i> ] [ <b>−C</b><i>cptfile</i> ] [ <b>−E</b> ] [ <b>−G</b><i>fill</i> ] [ <b>−I</b><i>xinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>][/<i>yinc</i>[<i>unit</i>][<b>=</b>|<b>+</b>]] ] [ <b>−K</b> ] [ <b>−N</b> ] [ <b>−O</b> ] [ <b>−P</b> ] [ <b>−Q</b><i>parameters</i> ] [ <b>−R</b><i>west</i>/<i>east</i>/<i>south</i>/<i>north</i>[<b>r</b>] ] [ <b>−S</b>[<b>l</b>]<i>scale</i> ] [ <b>−T</b> ] [ <b>−U</b>[<i>just</i>/<i>dx</i>/<i>dy</i>/][<b>c</b>|<i>label</i>] ] [ <b>−V</b> ] [ <b>−W</b><i>pen</i> ] [ <b>−X</b>[<b>a</b>|<b>c</b>|<b>r</b>][<i>x-shift</i>[<b>u</b>]] ] [ <b>−Y</b>[<b>a</b>|<b>c</b>|<b>r</b>][<i>y-shift</i>[<b>u</b>]] ] [ <b>−Z</b> ] [ <b>−c</b><i>copies</i> ] [ <b>−f</b>[<b>i</b>|<b>o</b>]<i>colinfo</i> ]</p> <a name="DESCRIPTION"></a> <h2>DESCRIPTION</h2> <p style="margin-left:11%; margin-top: 1em"><b>grdvector</b> 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). <b>grdvector</b> is basically a short-hand for using 2 calls to <b><A HREF="grd2xyz.html">grd2xyz</A></b> and pasting the output through <b>psxy −SV</b>. <i><br> compx.grd</i></p> <p style="margin-left:22%;">Contains the x-component of the vector field.</p> <p style="margin-left:11%;"><i>compy.grd</i></p> <p style="margin-left:22%;">Contains the y-component of the vector field. (See GRID FILE FORMATS below.)</p> <table width="100%" border=0 rules="none" frame="void" cellspacing="0" cellpadding="0"> <tr valign="top" align="left"> <td width="11%"></td> <td width="3%"> <p style="margin-top: 1em" valign="top"><b>−J</b></p> </td> <td width="8%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">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 <b><A HREF="gmtdefaults.html#MEASURE_UNIT">MEASURE_UNIT</A></b> setting in .gmtdefaults4, but this can be overridden on the command line by appending <b>c</b>, <b>i</b>, or <b>m</b> to the scale/width value. When central meridian is optional, default is center of longitude range on <b>−R</b> option. Default standard parallel is the equator. For map height, max dimension, or min dimension, append <b>h</b>, <b>+</b>, or <b>-</b> to the width, respectively.</p> </td> </table> <p style="margin-left:22%;">More details can be found in the <b><A HREF="psbasemap.html">psbasemap</A></b> man pages.</p> <p style="margin-left:22%; margin-top: 1em"><b>CYLINDRICAL PROJECTIONS:</b></p> <p style="margin-left:22%; margin-top: 1em"><b>−Jc</b><i>lon0/lat0/scale</i> (Cassini) <b><br> −Jcyl_stere</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i> (Cylindrical Stereographic) <b><br> −Jj</b>[<i>lon0/</i>]<i>scale</i> (Miller) <b><br> −Jm</b>[<i>lon0</i>/[<i>lat0/</i>]]<i>scale</i> (Mercator) <b><br> −Jm</b><i>lon0/lat0/scale</i> (Mercator - Give meridian and standard parallel) <b><br> −Jo</b>[<b>a</b>]<i>lon0/lat0/azimuth/scale</i> (Oblique Mercator - point and azimuth) <b><br> −Jo</b>[<b>b</b>]<i>lon0/lat0/lon1/lat1/scale</i> (Oblique Mercator - two points) <b><br> −Joc</b><i>lon0/lat0/lonp/latp/scale</i> (Oblique Mercator - point and pole) <b><br> −Jq</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i> (Cylindrical Equidistant) <b><br> −Jt</b><i>lon0/</i>[<i>lat0/</i>]<i>scale</i> (TM - Transverse Mercator) <b><br> −Ju</b><i>zone/scale</i> (UTM - Universal Transverse Mercator) <b><br> −Jy</b>[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i> (Cylindrical Equal-Area)</p> <p style="margin-left:22%; margin-top: 1em"><b>CONIC PROJECTIONS:</b></p> <p style="margin-left:22%; margin-top: 1em"><b>−Jb</b><i>lon0/lat0/lat1/lat2/scale</i> (Albers) <b><br> −Jd</b><i>lon0/lat0/lat1/lat2/scale</i> (Conic Equidistant) <b><br> −Jl</b><i>lon0/lat0/lat1/lat2/scale</i> (Lambert Conic Conformal) <b><br> −Jpoly</b>/[<i>lon0/</i>[<i>lat0/</i>]]<i>scale</i> ((American) Polyconic)</p> <p style="margin-left:22%; margin-top: 1em"><b>AZIMUTHAL PROJECTIONS:</b></p> <p style="margin-left:22%; margin-top: 1em"><b>−Ja</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i> (Lambert Azimuthal Equal-Area) <b><br> −Je</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i> (Azimuthal Equidistant) <b><br> −Jf</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i> (Gnomonic) <b><br> −Jg</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i> (Orthographic) <b><br> −Jg</b><i>lon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale</i> (General Perspective). <b><br> −Js</b><i>lon0/lat0</i>[<i>/horizon</i>]<i>/scale</i> (General Stereographic)</p> <p style="margin-left:22%; margin-top: 1em"><b>MISCELLANEOUS PROJECTIONS:</b></p> <p style="margin-left:22%; margin-top: 1em"><b>−Jh</b>[<i>lon0/</i>]<i>scale</i> (Hammer) <b><br> −Ji</b>[<i>lon0/</i>]<i>scale</i> (Sinusoidal) <b><br> −Jkf</b>[<i>lon0/</i>]<i>scale</i> (Eckert IV) <b><br> −Jk</b>[<b>s</b>][<i>lon0/</i>]<i>scale</i> (Eckert VI) <b><br> −Jn</b>[<i>lon0/</i>]<i>scale</i> (Robinson) <b><br> −Jr</b>[<i>lon0/</i>]<i>scale</i> (Winkel Tripel) <b><br> −Jv</b>[<i>lon0/</i>]<i>scale</i> (Van der Grinten) <b><br> −Jw</b>[<i>lon0/</i>]<i>scale</i> (Mollweide)</p> <p style="margin-left:22%; margin-top: 1em"><b>NON-GEOGRAPHICAL PROJECTIONS:</b></p> <p style="margin-left:22%; margin-top: 1em"><b>−Jp</b>[<b>a</b>]<i>scale</i>[<i>/origin</i>][<b>r</b>|<b>z</b>] (Polar coordinates (theta,r)) <b><br> −Jx</b><i>x-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>][<i>/y-scale</i>[<b>d</b>|<b>l</b>|<b>p</b><i>pow</i>|<b>t</b>|<b>T</b>]] (Linear, log, and power scaling)</p> <a name="OPTIONS"></a> <h2>OPTIONS</h2> <p style="margin-left:11%; margin-top: 1em">No space between the option flag and the associated arguments.</p> <table width="100%" border=0 rules="none" frame="void" cellspacing="0" cellpadding="0"> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−A</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Means grid files have polar (r, theta) components instead of Cartesian (x, y).</p> </td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−B</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Sets map boundary annotation and tickmark intervals; see the <b><A HREF="psbasemap.html">psbasemap</A></b> man page for all the details.</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−C</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Use <i>cptfile</i> to assign colors based on vector length.</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−E</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Center vectors on grid nodes [Default draws from grid node].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−G</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Sets color or shade for vector interiors [Default is no fill]. (See SPECIFYING FILL below).</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−I</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Only plot vectors at nodes every <i>x_inc, y_inc</i> apart (must be multiples of original grid spacing). Append <b>m</b> for minutes or <b>c</b> for seconds. [Default plots every node].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−K</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">More <i>PostScript</i> code will be appended later [Default terminates the plot system].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−N</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Do NOT clip vectors at map boundaries [Default will clip].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−O</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Selects Overlay plot mode [Default initializes a new plot system].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−P</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Selects Portrait plotting mode [Default is Landscape, see <b><A HREF="gmtdefaults.html">gmtdefaults</A></b> to change this].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−Q</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Select vector plot [Default is stick-plot]. Optionally, specify <i>parameters</i> which are <i>arrowwidth/headlength/headwidth</i> [Default is 0.075<b>c</b>/0.3<b>c</b>/0.25<b>c</b> (or 0.03<b>i</b>/0.12<b>i</b>/0.1<b>i</b>)]. Append <b>n</b><i>size</i> which will cause vectors shorter than <i>size</i> to have their appearance scaled by length/<i>size</i>.</p> </td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−R</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top"><i>xmin</i>, <i>xmax</i>, <i>ymin</i>, and <i>ymax</i> specify the Region of interest. For geographic regions, these limits correspond to <i>west, east, south,</i> and <i>north</i> and you may specify them in decimal degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append <b>r</b> if lower left and upper right map coordinates are given instead of w/e/s/n. The two shorthands <b>−Rg</b> and <b>−Rd</b> stand for global domain (0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude). Alternatively, specify the name of an existing grid file and the <b>−R</b> settings (and grid spacing, if applicable) are copied from the grid. For calendar time coordinates you may either give (a) relative time (relative to the selected <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b> and in the selected <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b>; append <b>t</b> to <b>−JX</b>|<b>x</b>), or (b) absolute time of the form [<i>date</i>]<b>T</b>[<i>clock</i>] (append <b>T</b> to <b>−JX</b>|<b>x</b>). At least one of <i>date</i> and <i>clock</i> must be present; the <b>T</b> is always required. The <i>date</i> string must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]] (ISO week calendar), while the <i>clock</i> string must be of the form hh:mm:ss[.xxx]. The use of delimiters and their type and positions must be exactly as indicated (however, input, output and plot formats are customizable; see <b><A HREF="gmtdefaults.html">gmtdefaults</A></b>). Specify a subset of the grid.</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−S</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Sets scale for vector length in data units per distance measurement unit [1]. Append <b>c</b>, <b>i</b>, <b>m</b>, <b>p</b> to indicate the measurement unit (cm, inch, m, point). Prepend <b>l</b> to indicate a fixed length for all vectors.</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−T</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Means azimuth should be converted to angles based on the selected map projection.</p> </td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−U</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Draw Unix System time stamp on plot. By adding <i>just/dx/dy/</i>, the user may specify the justification of the stamp and where the stamp should fall on the page relative to lower left corner of the plot. For example, BL/0/0 will align the lower left corner of the time stamp with the lower left corner of the plot. Optionally, append a <i>label</i>, or <b>c</b> (which will plot the command string.). The <b><A HREF="GMT.html">GMT</A></b> parameters <b><A HREF="gmtdefaults.html#UNIX_TIME">UNIX_TIME</A></b>, <b><A HREF="gmtdefaults.html#UNIX_TIME_POS">UNIX_TIME_POS</A></b>, and <b><A HREF="gmtdefaults.html#UNIX_TIME_FORMAT">UNIX_TIME_FORMAT</A></b> can affect the appearance; see the <b><A HREF="gmtdefaults.html">gmtdefaults</A></b> man page for details. The time string will be in the locale set by the environment variable <b>TZ</b> (generally local time).</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−V</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−W</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Set pen attributes used for vector outlines [Default: width = 0.25p, color = black, texture = solid]. (See SPECIFYING PENS below).</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−X −Y</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Shift plot origin relative to the current origin by (<i>x-shift,y-shift</i>) and optionally append the length unit (<b>c</b>, <b>i</b>, <b>m</b>, <b>p</b>). You can prepend <b>a</b> to shift the origin back to the original position after plotting, or prepend <b>r</b> [Default] to reset the current origin to the new location. If <b>−O</b> is used then the default (<i>x-shift,y-shift</i>) is (0,0), otherwise it is (r1i, r1i) or (r2.5c, r2.5c). Alternatively, give <b>c</b> to align the center coordinate (x or y) of the plot with the center of the page based on current page size.</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−Z</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Means the angles provided are azimuths rather than direction (requires <b>−A</b>).</p> </td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−c</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Specifies the number of plot copies. [Default is 1].</p></td> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p style="margin-top: 1em" valign="top"><b>−f</b></p> </td> <td width="4%"></td> <td width="78%"> <p style="margin-top: 1em" valign="top">Special formatting of input and/or output columns (time or geographical data). Specify <b>i</b> or <b>o</b> to make this apply only to input or output [Default applies to both]. Give one or more columns (or column ranges) separated by commas. Append <b>T</b> (absolute calendar time), <b>t</b> (relative time in chosen <b><A HREF="gmtdefaults.html#TIME_UNIT">TIME_UNIT</A></b> since <b><A HREF="gmtdefaults.html#TIME_EPOCH">TIME_EPOCH</A></b>), <b>x</b> (longitude), <b>y</b> (latitude), or <b>f</b> (floating point) to each column or column range item. Shorthand <b>−f</b>[<b>i</b>|<b>o</b>]<b>g</b> means <b>−f</b>[<b>i</b>|<b>o</b>]0<b>x</b>,1<b>y</b> (geographic coordinates).</p></td> </table> <p style="margin-left:11%; margin-top: 1em"><b>SPECIFYING PENS</b></p> <table width="100%" border=0 rules="none" frame="void" cellspacing="0" cellpadding="0"> <tr valign="top" align="left"> <td width="11%"></td> <td width="4%"> <p valign="top"><i>pen</i></p></td> <td width="7%"></td> <td width="78%"> <p valign="top">The attributes of lines and symbol outlines as defined by <i>pen</i> is a comma delimetered list of <i>width</i>, <i>color</i> and <i>texture</i>, each of which is optional. <i>width</i> can be indicated as a measure (points, centimeters, inches) or as <b>faint</b>, <b>thin</b>[<b>ner</b>|<b>nest</b>], <b>thick</b>[<b>er</b>|<b>est</b>], <b>fat</b>[<b>ter</b>|<b>test</b>], or <b>obese</b>. <i>color</i> specifies a gray shade or color (see SPECIFYING COLOR below). <i>texture</i> is a combination of dashes ‘-’ and dots ‘.’.</p></td> </table> <p style="margin-left:11%; margin-top: 1em"><b>SPECIFYING FILL</b></p> <table width="100%" border=0 rules="none" frame="void" cellspacing="0" cellpadding="0"> <tr valign="top" align="left"> <td width="11%"></td> <td width="6%"> <p valign="top"><i>fill</i></p></td> <td width="5%"></td> <td width="78%"> <p valign="top">The attribute <i>fill</i> specifies the solid shade or solid <i>color</i> (see SPECIFYING COLOR below) or the pattern used for filling polygons. Patterns are specified as <b>p</b><i>dpi/pattern</i>, where <i>pattern</i> gives the number of the built-in pattern (1-90) <i>or</i> the name of a Sun 1-, 8-, or 24-bit raster file. The <i>dpi</i> sets the resolution of the image. For 1-bit rasters: use <b>P</b><i>dpi/pattern</i> for inverse video, or append <b>:F</b><i>color</i>[<b>B</b>[<i>color</i>]] to specify fore- and background colors (use <i>color</i> = - for transparency). See <b><A HREF="GMT.html">GMT</A></b> Cookbook & Technical Reference Appendix E for information on individual patterns.</p> </td> </table> <p style="margin-left:11%; margin-top: 1em"><b>SPECIFYING COLOR</b></p> <table width="100%" border=0 rules="none" frame="void" cellspacing="0" cellpadding="0"> <tr valign="top" align="left"> <td width="11%"></td> <td width="7%"> <p valign="top"><i>color</i></p></td> <td width="4%"></td> <td width="78%"> <p valign="top">The <i>color</i> of lines, areas and patterns can be specified by a valid color name; by a gray shade (in the range 0−255); by a decimal color code (r/g/b, each in range 0−255; h-s-v, ranges 0−360, 0−1, 0−1; or c/m/y/k, each in range 0−1); or by a hexadecimal color code (#rrggbb, as used in HTML). See the <b><A HREF="gmtcolors.html">gmtcolors</A></b> manpage for more information and a full list of color names.</p></td> </table> <a name="GRID FILE FORMATS"></a> <h2>GRID FILE FORMATS</h2> <p style="margin-left:11%; margin-top: 1em"><b><A HREF="GMT.html">GMT</A></b> is able to recognize many of the commonly used grid file formats, as well as the precision, scale and offset of the values contained in the grid file. When <b><A HREF="GMT.html">GMT</A></b> needs a little help with that, you can add the suffix <b>=</b><i>id</i>[<b>/</b><i>scale</i><b>/</b><i>offset</i>[<b>/</b><i>nan</i>]], where <i>id</i> is a two-letter identifier of the grid type and precision, and <i>scale</i> and <i>offset</i> are optional scale factor and offset to be applied to all grid values, and <i>nan</i> is the value used to indicate missing data. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and Section 4.17 of the GMT Technical Reference and Cookbook for more information.</p> <p style="margin-left:11%; margin-top: 1em">When reading a netCDF file that contains multiple grids, <b><A HREF="GMT.html">GMT</A></b> will read, by default, the first 2-dimensional grid that can find in that file. To coax <b><A HREF="GMT.html">GMT</A></b> into reading another multi-dimensional variable in the grid file, append <b>?</b><i>varname</i> to the file name, where <i>varname</i> is the name of the variable. Note that you may need to escape the special meaning of <b>?</b> in your shell program by putting a backslash in front of it, or by placing the filename and suffix between quotes or double quotes. See <b><A HREF="grdreformat.html">grdreformat</A></b>(1) and Section 4.18 of the GMT Technical Reference and Cookbook for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.</p> <a name="EXAMPLES"></a> <h2>EXAMPLES</h2> <p style="margin-left:11%; margin-top: 1em">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 magnitudes so that 10 units equal 1 inch, run</p> <p style="margin-left:11%; margin-top: 1em"><b>grdvector</b> r.grd theta.grd <b>−Jx</b>5<b>c −A −Q −S</b>10<b>i</b> > gradient.ps</p> <a name="SEE ALSO"></a> <h2>SEE ALSO</h2> <p style="margin-left:11%; margin-top: 1em"><i><A HREF="GMT.html">GMT</A></i>(1), <i><A HREF="gmtcolors.html">gmtcolors</A></i>(5), <i><A HREF="grdcontour.html">grdcontour</A></i>(1), <i><A HREF="psxy.html">psxy</A></i>(1)</p> <hr> </body> </html>