grdinfo(1) [debian man page]

GRDINFO(l)																GRDINFO(l)

NAME

       grdinfo - Get information about the contents of a 2-D grd file

SYNOPSIS

       grdinfo grdfiles [ -C ] [ -D ] [ -F ] [ -L1 ] [ -L2 ] [ -M ] [ -V ]

DESCRIPTION

       grdinfo reads a 2-D binary grd file and reports various statistics for the (x,y,z) data in the grdfile. 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.

       grdfile
	      The name of one or several 2-D grd files.

OPTIONS

       No space between the option flag and the associated arguments.

       -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, respec-
	      tively.

       -D     Report grid domain and x/y-increments using dd:mm:ss[.fff] notation [Default is decimal].  Does not apply to the -C option.

       -F     Report grid domain and x/y-increments world mapping format [Default is generic].	Does not apply to the -C option.

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

       -L2    Report mean and standard deviation 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.

       -V     Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].

EXAMPLES

       To obtain all the information about the data set in file hawaii_topo.grd, try

       grdinfo -L1 -L2 -M hawaii_topo.grd

SEE ALSO

       gmt(1gmt), grd2cpt(1gmt), grd2xyz(1gmt), grdedit(1gmt)

								    1 Jan 2004								GRDINFO(l)

GRDTREND(l)															       GRDTREND(l)

NAME

       grdtrend - Fit and/or remove a polynomial trend in a grd file

SYNOPSIS

       grdtrend grdfile -Nn_model[r] [ -Ddiff.grd ] [ -Ttrend.grd ] [ -V ] [ -Wweight.grd ]

DESCRIPTION

       grdtrend  reads	a  2-D	gridded file and fits a low-order polynomial trend to these data by [optionally weighted] least-squares. The trend
       surface is defined by:

       m1 + m2*x + m3*y + m4*x*y + m5*x*x + m6*y*y + m7*x*x*x + m8*x*x*y + m9*x*y*y + m10*y*y*y.

       The user must specify -Nn_model, the number of model parameters to use; thus, -N4 fits a bilinear trend, -N6 a quadratic  surface,  and	so
       on.  Optionally, append r to the -N option to perform a robust fit. In this case, the program will iteratively reweight the data based on a
       robust scale estimate, in order to converge to a solution insensitive to outliers.  This may be handy when separating  a  "regional"  field
       from a "residual" which should have non-zero mean, such as a local mountain on a regional surface.

       If data file has values set to NaN, these will be ignored during fitting; if output files are written, these will also have NaN in the same
       locations.

       No space between the option flag and the associated arguments.

       grdfile
	      The name of a 2-D binary grd file.

       -N     [r]n_model sets the number of model parameters to fit. Prepend r for robust fit.

OPTIONS

       No space between the option flag and the associated arguments.

       -D     Write the difference (input data - trend) to the file diff.grd.

       -T     Write the fitted trend to the file trend.grd.

       -V     Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].

       -W     If weight.grd exists, it will be read and used to solve a weighted least-squares problem. [Default: Ordinary least-squares fit.]	If
	      the robust option has been selected, the weights used in the robust fit will be written to weight.grd.

REMARKS

       The  domain  of	x  and	y  will be shifted and scaled to [-1, 1] and the basis functions are built from Legendre polynomials. These have a
       numerical advantage in the form of the matrix which must be inverted and allow more accurate solutions. NOTE: The model	parameters  listed
       with  -V are Legendre polynomial coefficients; they are not numerically equivalent to the m#s in the equation described above. The descrip-
       tion above is to allow the user to match -N with the order of the polynomial surface.

EXAMPLES

       To remove a planar trend from hawaii_topo.grd and write result in hawaii_residual.grd, try

       grdtrend hawaii_topo.grd -N3 -Dhawaii_residual.grd

       To do a robust  fit  of	a  bicubic  surface  to  hawaii_topo.grd,  writing  the  result  in  hawaii_trend.grd  and  the  weights  used	in
       hawaii_weight.grd, and reporting the progress, try

       grdtrend hawaii_topo.grd -Nr10 -Thawaii_trend.grd -Whawaii_weight.grd -V

SEE ALSO

       gmt(1gmt), grdfft(1gmt), grdfilter(1gmt)

								    1 Jan 2004							       GRDTREND(l)