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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).


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


-C 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).

-F 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]

-L0 Report range of z after actually scanning the data, not just reporting what
the header says.

-L1 Report median and L1 scale of z (L1 scale = 1.4826 * Median Absolute
Deviation (MAD)).

-L2 Report mean, standard deviation, and root-mean-square (rms) of z.

-M 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.

-Tdz 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

Print GMT version and exit.

Print full path to GMT share directory and exit.


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

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