Provided by: gmt-common_5.4.5+dfsg-2_all bug


       grdimage - Project grids or images and plot them on maps


       grdimage grd_z | grd_r grd_g grd_b [  -Aout_img[=driver] ] [  -B[p|s]parameters ] [  -Ccpt
       ]   [    -D[r]   ]   [     -E[i|dpi]    ]     -Jparameters    [     -G[f|b]color    ]    [
       -I[intensfile|intensity|modifiers] ] [  -Jz|-Zparameters ] [  -K ] [  -M ] [  -N ] [  -O ]
       [  -P ] [  -Q ] [  -Rwest/east/south/north[/zmin/zmax][+r] ] [  -U[stamp] ] [  -V[level] ]
       [  -Xx_offset ] [  -Yy_offset ] [ -fflags ] [ -nflags ] [ -pflags ] [ -tr ]

       Note: No space is allowed between the option flag and the associated arguments.


       grdimage  reads  one 2-D grid file and produces a gray-shaded (or colored) map by plotting
       rectangles centered on each grid node and assigning them a gray-shade (or color) based  on
       the  z-value.  Alternatively, grdimage reads three 2-D grid 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 grid using grdgradient
       and,  optionally,  modified  by grdmath or grdhisteq. Yet as a third alternative available
       when GMT is build with GDAL support the grd_z file can be an image referenced or not (than
       see  -Dr).  In  this  case the images can be illuminated with the file provided via the -I
       option. Here if image has no coordinates those of the intensity file will be used.

       When using map projections, the grid is first resampled on a new rectangular grid with the
       same  dimensions.  Higher  resolution  images  can  be obtained by using the -E option. To
       obtain the resampled value (and hence shade or color) of each map pixel, its  location  is
       inversely  projected  back onto the input grid after which a value is interpolated between
       the surrounding input grid values. By default bi-cubic interpolation is used. Aliasing  is
       avoided  by  also  forward  projecting  the  input  grid  nodes.  If two or more nodes are
       projected onto the same pixel, their average will dominate in the calculation of the pixel
       value. Interpolation and aliasing is controlled with the -n option.

       The  -R  option  can be used to select a map region larger or smaller than that implied by
       the extent of the grid.

       A (color) PostScript file is output.


       grd_z | grd_r grd_g grd_b
              2-D gridded data set (or red, green, blue  grids)  to  be  imaged  (See  GRID  FILE
              FORMATS below.)

       -Jparameters (more ...)
              Select map projection.


              Save  an  image  in  a  raster  format  instead of PostScript. Use extension Append
              out_img to select the image file name and extension.  If the extension  is  one  of
              .bmp,  .gif, .jpg, .png, or .tif then no driver information is required.  For other
              output formats you must append the required GDAL driver.  The driver is the  driver
              code  name  used  by GDAL; see your GDAL installation's documentation for available
              drivers.  Notes: (1) If a tiff file (.tif) is selected then we will write a GeoTiff
              image  if  the  GMT  projection  syntax translates into a PROJ4 syntax, otherwise a
              plain tiff file is produced. (2) Any vector elements will be lost.

       -B[p|s]parameters (more ...)
              Set map boundary frame and axes attributes.

       -Ccpt  Name of the CPT (for grd_z only). Alternatively, supply the name  of  a  GMT  color
              master  dynamic  CPT [rainbow] to automatically determine a continuous CPT from the
              grid's z-range.  If the dynamic CPT has a default range then  that  range  will  be
              imposed instead.  Yet another option is to specify -Ccolor1,color2[,color3,...]  to
              build a linear continuous CPT from those colors automatically.  In this case color1
              etc  can  be  a  r/g/b  triplet,  a  color name, or an HTML hexadecimal color (e.g.
              #aabbcc ).

       -D[r]  Specifies that the grid supplied is an image file to be read  via  GDAL.  Obviously
              this option will work only with GMT versions built with GDAL support. The image can
              be indexed or true color (RGB) and can be an URL of a remotely located  file.  That
              is  -D  is  a valid file syntax. Note, however,
              that to use it this way you must not be blocked by a proxy. If you are, chances are
              good  that  it  can  work by setting the environmental variable http_proxy with the
              value 'your_proxy:port' Append r to use the region specified by -R to apply to  the
              image.   For  example,  if  you  have  used -Rd then the image will be assigned the
              limits of a global domain. The interest of this mode is that you can project a  raw
              image (an image without referencing coordinates).

              Sets  the resolution of the projected grid that will be created if a map projection
              other than Linear or Mercator was selected [100]. 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 grid file with intensities in the (-1,+1) range, or a constant
              intensity to apply everywhere; this simply affects the ambient light.  If just + is
              given then we derive an intensity grid from the input data grid grd_z via a call to
              grdgradient using the arguments -A-45 and -Nt1 for  that  module.  You  can  append
              +aazimuth  and  **+n*args  to  override  those  values.   If you want more specific
              intensities then run grdgradient separately first.  [Default is no illumination].

       -Jz|Zparameters (more ...)
              Set z-axis scaling; same syntax as -Jx.

       -K (more ...)
              Do not finalize the PostScript plot.

       -M     Force conversion to monochrome image using  the  (television)  YIQ  transformation.
              Cannot be used with -Q.

       -N     Do not clip the image at the map boundary (only relevant for non-rectangular maps).

       -O (more ...)
              Append to existing PostScript plot.

       -P (more ...)
              Select "Portrait" plot orientation.

       -Q     Make  grid  nodes  with  z  =  NaN  transparent,  using the colormasking feature in
              PostScript Level 3 (the PS device must support PS Level 3).

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
              Specify the region of interest.

       For perspective view p, optionally append /zmin/zmax. (more ...) 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 grid file will result in a subset of the  grid  [Default  is  the  region
       given by the grid file].

       -U[[just]/dx/dy/][c|label] (more ...)
              Draw GMT time stamp logo on plot.

       -V[level] (more ...)
              Select verbosity level [c].


       -Y[a|c|f|r][y-shift[u]] (more ...)
              Shift plot origin.

       -f[i|o]colinfo (more ...)
              Specify data types of input and/or output columns.

       -n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more ...)
              Select interpolation mode for grids.

       -p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0] (more ...)
              Select perspective view.

       -t[transp] (more ...)
              Set PDF transparency level in percent.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print  a  complete  usage (help) message, including the explanation of all options,
              then exits.


       By default GMT writes out grid as single precision floats  in  a  COARDS-complaint  netCDF
       file  format.  However, GMT is able to produce grid files in many other commonly used grid
       file formats and also facilitates so called "packing" of grids, writing out floating point
       data as 1- or 2-byte integers. (more ...)


       Be aware that if your input grid contains patches of NaNs, these patches can become larger
       as a consequence of the resampling that must take place with most map projections. Because
       grdimage  uses the PostScript colorimage operator, for most non-linear projections we must
       resample your grid onto an equidistant rectangular lattice. If you find that the NaN areas
       are  not  treated adequately, consider (a) use a linear projection, or (b) use grdview -Ts


       Except for Cartesian cases, we need to resample your geographic grid onto  an  equidistant
       projected  grid. In doing so various algorithms come into play that projects data from one
       lattice to another while avoiding anti-aliasing, leading  to  possible  distortions.   One
       expected  effect  of resampling with splines is the tendency for the new resampled grid to
       slightly exceed the global min/max limits of the original grid.  If this is  coupled  with
       tight  CPT  limits  you  may find that some map areas may show up with fore- or background
       color due to the resampling.  In that case you have two options: (1) Modify  your  CPT  to
       fit the resampled extrema (reported with -V) or (2) Impose clipping of resampled values so
       they do not exceed the input min/max values (add +c to your -n option).


       For a quick-and-dirty illuminated color map of the data in the  file,  with  the
       maximum map dimension limited to be 6 inches, try

              gmt grdimage -JX6i+ -I+ >

       To  gray-shade the file 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:

              gmt grdimage -Jl18/24/1.5c -Cshades.cpt -B1 >

       To create an illuminated color PostScript plot of the gridded data set, using the
       intensities  provided by the file, and color levels in the file colors.cpt, with
       linear scaling at 10 inch/x-unit, tickmarks every 5 units:

              gmt grdimage -Jx10i -Ccolors.cpt -B5 >

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

              gmt grdimage -Jx10i -B5 >

       When  GDAL  support  is  built in: To create a sinusoidal projection of a remotely located
       Jessica Rabbit

              gmt grdimage -JI15c -Rd -Dr \
                  -P >


       gmt, gmt.conf, grd2rgb, grdcontour, grdview, grdgradient, grdhisteq


       2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe