B.2.4 Native binary grid files

The old style native grid file format that was common in earlier version of GMT is still supported, although the use of netCDF files is strongly recommended. The file starts with a header containing a number of attributes defining the content. The grdedit utility program will allow you to edit parts of the header of an existing grdfile. The attributes listed in Table B.2 are contained within the header record in the order given (except the $z$-array which is not part of the header structure, but makes up the rest of the file).

Table B.2: GMT gridded file header record. TYPE can be char, short, int, float, or double.

Parameter	Description
int nx	Number of nodes in the $x$-dimension
int ny	Number of nodes in the y-dimension
int node_offset	0 for grid line registration, 1 for pixel registration
double x_min	Minimum $x$-value of region
double x_max	Maximum $x$-value of region
double y_min	Minimum $y$-value of region
double y_max	Maximum $y$-value of region
double z_min	Minimum $z$-value in data set
double z_max	Maximum $z$-value in data set
double x_inc	Node spacing in $x$-dimension
double y_inc	Node spacing in $y$-dimension
double z_scale_factor	Factor to multiply $z$-values after read
double z_add_offset	Offset to add to scaled $z$-values
char x_units[80]	Units of the $x$-dimension
char y_units[80]	Units of the $y$-dimension
char z_units[80]	Units of the $z$-dimension
char title[80]	Descriptive title of the data set
char command[320]	Command line that produced the grdfile
char remark[160]	Any additional comments
TYPE z[nx*ny]	1-D array with $z$-values in scanline format