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] ] [
-S[l]scale ] [ -T ] [ -U[/dx/dy/][label] ] [ -V ] [ -Wcontourpen ] [
-Xx-shift ] [ -Yy-shift ] [ -Z ] [ -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 draw-
ing 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 UNIT/degree, 1:xxxxx, or
width in UNIT (upper case modifier). UNIT is cm, inch, or m,
depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
can be overridden on the command line by appending c, i, or m to
the scale/width value. For map height, max dimension, or min
dimension, append h, +, or - to the width, respectively.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard paral-
lel)
-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 Car-
ree))
-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/[slat/]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:
-Jp[a]scale[/origin] (polar (theta,r) coordinates, optional a
for azimuths and offset theta [0])
-Jxx-scale[l|ppow][/y-scale[l|ppow]][d] (Linear, log, and power
scaling)
More details can be found in the psbasemap man pages.
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 annotation and tickmark intervals; see the
psbasemap man page for all the 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, each in 0-255, h/s/v,
with h in 0-360, s, and v in 0-1, and set COLOR_MODEL = hsv, or
c/m/y/k, each in 0-100 %). Alternatively, specify -Gpdpi/pat-
tern, 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. The
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 sys-
tem].
-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 [Default is
0.075c/0.3c/0.25c (or 0.03i/0.12i/0.1i)]. Append nsize which
will cause vectors shorter than size to have their appearance
scaled by length/size.
-R xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of wesn. The
two shorthands -Rg -Rd stand for global domain (0/360 or
-180/+180 in longitude respectively, with -90/+90 in latitude).
For calendar time coordinates you may either give relative time
(relative to the selected TIME_EPOCH and in the selected
TIME_UNIT; append t to -JX|x), or absolute time of the form
[date]T[clock] (append T to -JX|x). At least one of date and
clock must be present; the T is always required. The date string
must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
yyyy[-Www[-d]] (ISO week calendar), while the clock string must
be of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be as indicated (however, input/output
and plotting formats are flexible). Specify a subset of the
grid.
-S Sets scale for vector length in data units per distance measure-
ment unit [1]. Append c, i, m, p to indicate the measurement
unit (cm, inch, m, point). Prepend l to indicate a fixed length
for all vectors.
-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. Optionally, append a label, or c
(which will plot the command string.). The GMT parameters
UNIX_TIME and UNIX_TIME_POS can affect the appearance; see the
gmtdefaults man page for details.
-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). Prepend a for abso-
lute coordinates; the default (r) will reset plot origin. Give
c to center plot using current page size.
-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 5 cm per data unit, using vector rather than
stick plot, and scale vector magnitudes so that 10 units equal 1 inch,
run
grdvector r.grd theta.grd -Jx5c -A -Q -S10i > gradient.ps
SEE ALSO
gmt(l), grdcontour(l), psxy(l)
GMT4.0 1 Oct 2004 GRDVECTOR(l)
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