grdimage − Create grayshaded or colored image from a 2-D netCDF grd file


grdimage grd_z | grd_r grd_g grd_b −Ccptfile −Jparameters [ −Btickinfo ] [ −Ei|dpi ] [ −G[f|b]rgb ] [ −Iintensfile] [ −K ] [ −M ] [ −O ] [ −P ] [ −Q ] [ −Rwest/east/south/north[r] ] [ −Ssearch_radius ] [ −T[s][o[pen]] ] [ −U[/dx/dy/][label] ] [ −V ] [ −Xx-shift ] [ −Yy-shift ] [ −ccopies ]


grdimage reads one 2-D gridded file and produces a gray-shaded (or colored) map by assigning each z-value a gray-shade (or color). Alternatively, grdimage reads three 2-D gridded files with the red, green, and blue components directly (all must be in the 0-255 range). 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.

grd_z | grd_r grd_g grd_b

2-D gridded data set (or red, green, blue grids) to be imaged


name of the color palette table (for grd_z only).


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.

More details can be found in the psbasemap man pages.


−Jclon0/lat0/scale (Cassini)
lon0/scale (Miller)
scale (Mercator - Greenwich and Equator as origin)
lon0/lat0/scale (Mercator - Give meridian and standard parallel)
lon0/lat0/azimuth/scale (Oblique Mercator - point and azimuth)
lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
lon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
lon0/scale (Equidistant Cylindrical Projection (Plate Carree))
lon0/scale (TM - Transverse Mercator, with Equator as y = 0)
lon0/lat0/scale (TM - Transverse Mercator, set origin)
zone/scale (UTM - Universal Transverse Mercator)
lon0/lats/scale (Basic Cylindrical Projection)


−Jalon0/lat0/scale (Lambert)
lon0/lat0/scale (Equidistant)
lon0/lat0/horizon/scale (Gnomonic)
lon0/lat0/scale (Orthographic)
lon0/lat0/[slat/]scale (General Stereographic)


−Jblon0/lat0/lat1/lat2/scale (Albers)
lon0/lat0/lat1/lat2/scale (Equidistant)
lon0/lat0/lat1/lat2/scale (Lambert)


−Jhlon0/scale (Hammer)
lon0/scale (Sinusoidal)
[f|s]lon0/scale (Eckert IV (f) and VI (s))
lon0/scale (Robinson)
lon0/scale (Winkel Tripel)
lon0/scale (Van der Grinten)
lon0/scale (Mollweide)


−Jp[a]scale[/origin][r] (Polar coordinates (theta,r))
x-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log, and power scaling)


No space between the option flag and the associated arguments.


Sets map boundary annotation and tickmark intervals; see the psbasemap man page for all the details.


Sets the resolution of the projected grid that will be created if a map projection other than Linear or Mercator was selected. By default, the projected grid will be of the same size (rows and columns) as the input file. Specify i to use the PostScript image operator to interpolate the image at the device resolution.


This option only applies when the resulting image otherwise 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 paint the mask (or its inverse, with −Gb) with the given color combination.


Gives the name of a grdfile with intensities in the (-1,+1) range. [Default is no illumination].


More PostScript code will be appended later [Default terminates the plot system].


Force conversion to monochrome image using the (television) YIQ transformation.


Selects Overlay plot mode [Default initializes a new plot system].


Selects Portrait plotting mode [GMT Default is Landscape, see gmtdefaults to change this].


Mask out nodes with z = NaN using the colormasking feature in PostScript Level 3 (the PS device must support PS Level 3).


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[][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). 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].


Set the search radius for the averaging procedure [Default avoids aliasing].


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. Optionally, append o to draw the tile outlines, and specify a custom pen if the default pen is not to your liking.


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.


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. Give c to center plot using current page size.


Specifies the number of plot copies. [Default is 1].


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 standard parallels 18 and 24, and using 1 degree tickmarks:

grdimage hawaii_grav.grd −Jl18/24/1.5c −Cshades.cpt −B1 >

To create an illuminated color PostScript plot of the gridded 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:

grdimage image.grd −Jx10i −Ccolors.cpt −Iintens.grd −B5 >

To create an false color PostScript plot from the three gridded files red.grd, green.grd, and blue.grd, with linear scaling at 10 inch/x-unit, tickmarks every 5 units:

grdimage red.grd green.grd blue.grd −Jx10i −B5 >


GMT(l), gmt2rgb(l), grdcontour(l), grdview(l), grdgradient(l), grdhisteq(l)