Create KML image quadtree from single grid


gmt grd2kml grid [ -Ccpt ] [ -EURL ] [ -Ffiltercode ] [ -Hfactor ] [ -I[intensfile|intensity|modifiers] ] [ -Ltilesize ] [ -Nprefix ] [ -Q ] [ -Ttitle ] [ -Wcfile|pen ] [ -V[level] ] [ -fflags ] [ --PAR=value ]

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


grd2kml reads a 2-D grid file and makes a quadtree of PNG images and KML wrappers for Google Earth using the selected tile size [256x256 pixels]. We downsample the grid depending on the viewing level in the quadtree using a Gaussian filter, but other filters can be selected as well. Optionally, illumination may be added by providing a grid file with intensities in the (-1,+1) range or by giving instructions to derive intensities from the input data grid automatically (see -I). Values outside the (-1,+1) intensity range will be clipped. Map colors are specified via a color palette lookup table. Contour overlays are optional.

Required Arguments

A 2-D gridded data set (See GRID FILE FORMATS below.)

Optional Arguments

Name of the color palette table (CPT). 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. Another option is to specify -Ccolor1,color2[,color3,…] to build a linear continuous CPT from those colors automatically, scaled to fit the data range. In this case color1 etc can be a r/g/b triplet, a color name, or an HTML hexadecimal color (e.g. #aabbcc ).
Instead of hosting all files on your computer, you may prepend a remote site URL. Then, the top-level prefix.kml file will use this URL to find all other files it references. After building completes you must place the entire prefix directory at the remote location pointed to by the URL [local files only]. With this arrangement you can share the prefix.kml with others (say, via email or for download) and users can open the file in their Google Earth and access the remote files from your server as needed.


Specifies the filter to use for the downsampling of the grid for more distant viewing. Choose among boxcar, cosine arch, gaussian, or median [Gaussian]. The filter width is set automatically depending on the level.
Improve the quality of rasterization by passing the sub-pixel smoothing factor to psconvert (same as -H option in psconvert) [no sub-pixel smoothing].
Gives the name of a grid file with intensities in the (-1,+1) range, or a constant intensity to apply everywhere (affects the ambient light). Alternatively, derive an intensity grid from the input data grid grid via a call to grdgradient; append +aazimuth and +nargs to specify azimuth and intensity arguments for that module or just give +d to select the default arguments (+a-45+nt1). If you want a more specific intensity scenario then run grdgradient separately first. [Default is no illumination].
Sets the fixed size of the image building blocks. Must be an integer that is radix 2. Typical values are 256 or 512 [256].
Sets a unique name prefixed used for the top-level KML filename and the directory where all referenced KML files and PNG images will be written [GMT_Quadtree].
Make grid nodes with z = NaN transparent, using the color-masking feature in PostScript Level 3 (the PS device must support PS Level 3).
Sets the title of the top-level document (i.e., its description).
-V[level] (more …)
Select verbosity level [c].
Supply a file with records each holding a contour value and a contour pen. We then overlay the selected contour lines on top of the image [no contours]. If cfile is not a valid file we assume you instead gave a pen and want to draw all the contours implied by the cpt in effect.
-f[i|o]colinfo (more …)
Specify data types of input and/or output columns.


The intensity grid can be created from the data grid using grdgradient and, optionally, modified by grdmath or grdhisteq. Custom intensity grids built with several different illumination angles can be combined with grdmath. For a single illumination angle the automatic illumination can be used instead.


To make a quadtree image representation of the large topography grid file, using the default tile size, supply automatic shading based on the topography, and use the larger 512x512 tiles, supplying a suitable title, and using color masking for unmapped area, try

gmt grd2kml -I+d -Nellice -L512 -Q -T"Ellice Basin Bathymetry"