grdinfo man page
grdinfo — Extract information from grids
Synopsis
grdinfo grdfiles [ C ] [ D[xoff[/yoff][+n] ] [ F ] [ I[dx[/dy]bir] ] [ L[012pa] ] [ M ] [ Rregion ] [ T[dz][+a[alpha]][+s] ] [ V[level] ] [ fflags ]
Note: No space is allowed between the option flag and the associated arguments.
Description
grdinfo reads a 2D 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 yincrements, and the number of x and y nodes, and [optionally] the mean, standard deviation, and/or the median, median absolute deviation of z, and/or the mode (LMS), LMS scale of z, and number of nodes set to NaN. We also report if the grid is pixel or gridlineregistered and if it is a Cartesian or Geographic data set (based on metadata in the file).
Required Arguments
 grdfile
The name of one or several 2D grid files. (See Grid File Formats below.)
Optional Arguments
 C
Formats the report using tabseparated 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).
 D[xoff[/yoff][+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.
 F
Report grid domain and x/yincrements in world mapping format [Default is generic]. Does not apply to the C option.
 I[dx[/dy]bir]
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.
 L[012pa]

 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 rootmeansquare (rms) of z.
 Lp
Report mode (LMS) and LMS scale of z.
 La
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.
 M
Find and report the location of min/max zvalues, 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.
 T[dz][+a[alpha]][+s]
Determine min and max zvalue. 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[io]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 just use ).
 + or just +
Print an extensive usage (help) message, including the explanation of any modulespecific 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.
Grid File Formats
By default GMT writes out grid as single precision floats in a COARDScomplaint 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 2byte integers. (more …)
Examples
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
Copyright
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe