NAME
grdimage - Create grayshaded or colored image from a 2-D
netCDF grd file
SYNOPSIS
grdimage grdfile -Ccptfile -Jparameters [ -Btickinfo ] [
-Edpi ] [ -G[f|b]rgb ] [ -Iintensfile] [ -K ] [ -M ] [ -O ]
[ -P ] [ -Rwest/east/south/north[r] ] [ -Ssearch_radius ] [
-T[s] ] [ -U[/dx/dy/][label] ] [ -V ] [ -Xx-shift ] [ -Yy-
shift ] [ -ccopies ]
DESCRIPTION
grdimage reads a 2-D gridded file and produces a gray-shaded
(or colored) map by assigning each contour interval a gray-
shade (or color). Optionally, illumination may be added by
providing a file with intensities in the (-1,+1) range.
Values outside this range will be clipped. Such intensity
files can be created from the grdfile using grdgradient and
modified by grdmath or grdhisteq. Each grid-node in the
grdfile is represented as a shaded (or colored) rectangle
centered on the grid node. When using map projections, the
grid is first resampled on a new rectangular grid (This can
be a time-consuming process for large grid files; but see
-T). A 24-bit true color PostScript file is output. The
region option can be used to select a map region larger or
smaller than that implied by the extent of the grdfile.
grdfile
2-D gridded data set to be imaged
-C name of the color palette table
-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 set-
ting in .gmtdefaults, but this can be overridden on the
command line by appending the c, i, or m to the
scale/width value.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and stan-
dard 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 ori-
gin)
-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[/origin] (polar (theta,r) coordinates, option-
ally offset theta [0])
-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 argu-
ments.
-B Sets map boundary tickmark intervals. See psbasemap for
details.
-E Sets the resolution of the projected grid that will be
created if a map projection other than Linear or Merca-
tor was selected. By default, the projected grid will
be of the same size (rows and columns) as the input
file.
-G This option only applies when the resulting image oth-
erwise would consist of only two colors: black (0) and
white (255). If so, this option will instead use the
image as a transparent mask and point the mask (or its
inverse, with -Gb) with the given color combination.
-I Gives the name of a grdfile with intensities in the (-
1,+1) range. [Default is no illumination].
-K More PostScript code will be appended later [Default
terminates the plot system].
-M Force conversion to monochrome image using the (televi-
sion) YIQ transformation.
-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].
-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. You may ask for a larger w/e/s/n
region to have more room between the image and the
axes. A smaller region than specified in the grdfile
will result in a subset of the grid [Default is region
given by the grdfile].
-S Set the search radius for the averaging procedure
[Default avoids aliasing].
-T Plot image without any interpolation. This involves
converting each node-centered bin into a polygon which
is then painted separately. Append s to skip nodes
with z = NaN. This option is useful for categorical
data where interpolating between values is meaningless.
-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.)
-V Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].
-X -Y
Shift origin of plot by (x-shift,y-shift). Prepend a
for absolute coordinates; the default (r) will reset
plot origin.
-c Specifies the number of plot copies. [Default is 1]
EXAMPLES
To gray-shade the file hawaii_grav.grd with shades given in
shades.cpt on a Lambert map at 1.5 cm/degree along the stan-
dard parallels 18 and 24, and using 1 degree tickmarks, try
grdimage hawaii_grav.grd -Jl18/24/1.5c -Cshades.cpt -B1 >
hawaii_grav_image.ps
To create an illuminated color PostScript plot of the grid-
ded data set image.grd, using the intensities provided by
the file intens.grd, and color levels in the file
colors.cpt, with linear scaling at 10 inch/x-unit, tickmarks
every 5 units, try
grdimage image.grd -Jx10i -Ccolors.cpt -Iintens.grd -B5 >
image.ps
SEE ALSO
gmt(l), grdcontour(l), grdview(l), grdgradient(l),
grdhisteq(l)