grdinfo man page

grdinfo — Extract information from grids


grdinfo grdfiles [ ] [ ] [ [dx[/dy]|r|b] ] [ [0|1|2] ] [ ] [ region ] [ [s]dz ] [ [level] ] [ -f<flags> ]

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, L1 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 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. 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).
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. 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.
-L[0 | 1 | 2]
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.
Find and report the location of min/max z-values, and count and report the number of nodes set to NaN, if any.
-R[unit]xmin/xmax/ymin/ymax[r] (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, round off to multiples of dz, and report as the text string -Tzmin/zmax/dz for use by makecpt. To get a symmetrical range about zero, using the max absolute multiple of dz, use -Tsdz instead.
-V[level] (more ...)
Select verbosity level [c].
-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.
-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
-+ 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 options, then exits.
Print GMT version and exit.
Print full path to GMT share directory and exit.

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. To specify the precision, scale and offset, the user should add the suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of the grid type and precision, and scale and offset are optional scale factor and offset to be applied to all grid values, and nan is the value used to indicate missing data. In case the two characters id is not provided, as in =/scale than a id=nf is assumed. When reading grids, the format is generally automatically recognized. If not, the same suffix can be added to input grid file names. See grdconvert and Section grid-file-format of the GMT Technical Reference and Cookbook for more information.

When reading a netCDF file that contains multiple grids, GMT will read, by default, the first 2-dimensional grid that can find in that file. To coax GMT into reading another multi-dimensional variable in the grid file, append ?varname to the file name, where varname is the name of the variable. Note that you may need to escape the special meaning of ? in your shell program by putting a backslash in front of it, or by placing the filename and suffix between quotes or double quotes. The ?varname suffix can also be used for output grids to specify a variable name different from the default: "z". See grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical Reference and Cookbook for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.


To obtain all the information about the data set in file hawaii_topo.nc:

gmt grdinfo -L1 -L2 -M hawaii_topo.nc

See Also

gmt, grd2cpt, grd2xyz, grdedit


GMT 5.2.1 November 12, 2015