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<title>GRDVECTOR</title>
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<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
IV) <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 = 1, 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>
