Extract information from grids


gmt grdinfo grdfiles [ -C[n|t] ] [ -D[xoff[/yoff]][+i] ] [ -F ] [ -I[dx[/dy]|b|i|r] ] [ -L[0|1|2|p|a] ] [ -M ] [ -Rregion ] [ -T[dz][+a[alpha]][+s] ] [ -V[level] ] [ -fflags ] [ -hheaders ] [ -oflags ] [ --PAR=value ]

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


grdinfo reads a 2-D binary grid file and reports metadata and various statistics for the (x,y,z) data in the grid file(s). The output information contains the minimum/maximum values for x, y, and z, where the min/max of z occur, the x- and y-increments, and the number of x and y nodes, and [optionally] the mean, standard deviation, and/or the median, median absolute deviation (MAD) of z, and/or the mode (Least Median of Squares; LMS), LMS scale of z, and number of nodes set to NaN. We also report if the grid is pixel- or gridline-registered and if it is a Cartesian or Geographic data set (based on metadata in the file).

Required Arguments

The name of one or several 2-D grid files. (See GRID FILE FORMATS below.)

Optional Arguments

Formats the report using tab-separated fields on a single line. The output is name w e s n z0 z1 dx dy nx ny[ x0 y0 x1 y1 ] [ med scale ] [mean std rms] [n_nan]. The data in brackets are output only if the corresponding options -M, -L1, -L2, and -M are used, respectively. Use -Ct to place file name at the end of the output record or -Cn to only output numerical columns. If the -I option is used, the output format is instead NF w e s n z0 z1, where NF is the total number of grids read and w e s n are rounded off (see -I).
Divide a single grid’s domain (or the -R domain, if no grid given) into tiles of size dx times dy (set via -I). You can specify overlap between tiles by appending xoff[/yoff]. If the single grid is given you may use the modifier +i to ignore tiles that have no data within each tile subregion. Default output is text region strings. Use -C to instead report four columns with xmin xmax ymin ymax per tile, or use -Ct to also have the region string appended as trailing text.
Report grid domain and x/y-increments in world mapping format [Default is generic]. Does not apply to the -C option.
Report the min/max of the region to the nearest multiple of dx and dy, and output this in the form -Rw/e/s/n (unless -C is set). To report the actual grid region, select -Ir. For a grid produced by the img supplement (a Cartesian Mercator grid), the exact geographic region is given with -Ii (if not found then we return the actual grid region instead). If no argument is given then we report the grid increment in the form -Ixinc[/yinc]. If -Ib is given we write each grid’s bounding box polygon instead. Finally, if -D is in effect then dx and dy are the dimensions of the desired tiles.
Report range of z after actually scanning the data, not just reporting what the header says.
Report median and L1 scale of z (L1 scale = 1.4826 * Median Absolute Deviation (MAD)).
Report mean, standard deviation, and root-mean-square (rms) of z.
Report mode (LMS) and LMS scale of z.
All of the above.

Note: If the grid is geographic then each node represents a physical area that decreases with increasing latitude. We therefore report spherically weighted statistical estimates for such grids.

Find and report the location of min/max z-values, and count and report the number of nodes set to NaN, if any.
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
Specify the region of interest. Using the -R option will select a subsection of the input grid(s). If this subsection exceeds the boundaries of the grid, only the common region will be extracted.
Determine min and max z-value. If dz is provided then we first round these values off to multiples of dz. To exclude the two tails of the distribution when determining the min and max you can add +a to set the alpha value (in percent [2]): We then sort the grid, exclude the data in the 0.5*alpha and 100 - 0.5*alpha tails, and revise the min and max. To force a symmetrical range about zero, using minus/plus the max absolute value of the two extremes, append +s. We report the result via the text string -Tzmin/zmax or -Tzmin/zmax/dz (if dz was given) as expected by makecpt.
-V[level] (more …)
Select verbosity level [c].
-f[i|o]colinfo (more …)
Specify data types of input and/or output columns.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more …)
Skip or produce header record(s).
-ocols[,…][t[word]] (more …)
Select output columns (0 is first column; t is trailing text, append word to write one word only).
-^ 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.
Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.

Grid File Formats

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 …)


To obtain all the information about the remote data set in file earth_relief_10m:

gmt grdinfo -L1 -L2 -M @earth_relief_10m

Get the grid spacing in earth_relief_10m:

dx=`gmt grdinfo -Cn -o7 @earth_relief_10m`