grdedit(1gmt)
NAME
grdedit - Modify header or content of a grid
SYNOPSIS
grdedit grid [ -A ] [ -C ] [ -Dxname/yname/zname/scale/offset/invalid/title/remark ] [ -E[a|h|l|r|t|v] ] [ -Goutgrid ] [ -Jparameters ] [ -Ntable ] [ -Rregion ] [ -S ] [ -T ] [ -V[level] ] [ -bibinary ] [ -dinodata ] [ -fflags ] [ -:[i|o] ] Note: No space is allowed between the option flag and the associated arguments.
DESCRIPTION
grdedit reads the header information in a binary 2-D grid file and replaces the information with values provided on the command line [if any]. As an option, global, geographical grids (with 360 degrees longitude range) can be rotated in the east-west direction, and individual nodal values can be replaced from a table of x, y, z values. grdedit only operates on files containing a grid header. Note: If it is important to retain the original data you should use -G to save the modified grid to a new file.
REQUIRED ARGUMENTS
grid Name of the 2-D grid file to modify. (See GRID FILE FORMATS
below).
OPTIONAL ARGUMENTS
-A If necessary, adjust the file's x_inc, y_inc to be compatible
with its domain (or a new domain set with -R). Older grid files
(i.e., created prior to GMT 3.1) often had excessive slop in
x_inc, y_inc and an adjustment is necessary. Newer files are
created correctly.
-C Clear the command history from the grid header.
-Dxname/yname/zname/scale/offset/invalid/title/remark
Give values for xname, yname, zname (give the names of those
variables and in square bracket their units, e.g., "distance
[km]"), scale (to multiply grid values after read [normally 1]),
offset (to add to grid after scaling [normally 0]), invalid (a
value to represent missing data [NaN]), title (anything you
like), and remark (anything you like). To leave some of these
values untouched, leave field blank. Empty fields in the end may
be skipped. Alternatively, to allow "/" to be part of one of the
values, use any non-alphanumeric character (and not the equal
sign) as separator by both starting and ending with it. For
example: -D:xname:yname:zname:scale:offset:invalid:title:remark:
Use quotes to group texts with more than one word. Note that
for geographic grids (-fg) xname and yname are set
automatically.
-E[a|h|l|r|t|v]
Transform the grid in one of six ways and (for l|r|t)
interchange the x and y information: -Ea will rotate the grid
around 180 degrees, -Eh will flip the grid horizontally
(left-to-right), -El will rotate the grid 90 degrees
counter-clockwise (left), -Er will rotate the grid 90 degrees
clockwise (right), -Et will transpose the grid [Default], -Ev
will flip the grid vertically (top-to-bottom). Incompatible
with the other options (except -G).
-Goutgrid
Normally, grdedit will overwrite the existing grid with the
modified grid. Use -G to write the modified grid to the file
outgrid instead.
-Jparameters (more ...)
Select map projection. Use the -J syntax to save the
georeferencing info as CF-1 compliant metadata in netCDF grids.
This metadata will be recognized by GDAL.
-Ntable
Read the ASCII (or binary; see -bi) file table and replace the
corresponding nodal values in the grid with these x,y,z values.
-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest. The new w/e/s/n values will
replace those in the grid, and the x_inc, y_inc values are
adjusted, if necessary.
-S For global, geographical grids only. Grid values will be shifted
longitudinally according to the new borders given in -R.
-T Make necessary changes in the header to convert a
gridline-registered grid to a pixel-registered grid, or
vice-versa. Basically, gridline-registered grids will have
their domain extended by half the x- and y-increments whereas
pixel-registered grids will have their domain shrunk by the same
amount.
-V[level] (more ...)
Select verbosity level [c].
-bi[ncols][t] (more ...)
Select native binary input. [Default is 3 input columns].
-dinodata (more ...)
Replace input columns that equal nodata with NaN.
-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).
-^ 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.
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. (more ...)
GEOGRAPHICAL AND TIME COORDINATES
When the output grid type is netCDF, the coordinates will be labeled "longitude", "latitude", or "time" based on the attributes of the input data or grid (if any) or on the -f or -R options. For example, both -f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid. When the x, y, or z coordinate is time, it will be stored in the grid as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH in the gmt.conf file or on the command line. In addition, the unit attribute of the time variable will indicate both this unit and epoch.
EXAMPLES
Let us assume the file data.nc covers the area 300/310/10/30. We want
to change the boundaries from geodetic longitudes to geographic and put
a new title in the header. We accomplish this by
gmt grdedit data.nc -R-60/-50/10/30 -D//////"Gravity Anomalies"
The grid world.nc has the limits 0/360/-72/72. To shift the data so
that the limits would be -180/180/-72/72, use
gmt grdedit world.nc -R-180/180/-72/72 -S
The file junk.nc was created prior to GMT 3.1 with incompatible -R and
-I arguments. To reset the x- and y-increments we run
gmt grdedit junk.nc -A
The file junk.nc was created prior to GMT 4.1.3 and does not contain
the required information to indicate that the grid is geographic. To
add this information, run
gmt grdedit junk.nc -fg
To rotate the grid oblique.nc 90 degrees counter-clockwise and write
out the rotated grid to a new file, run
gmt grdedit oblique.nc -El -Goblique_rot.nc
SEE ALSO
gmt, grd2xyz, grdinfo xyz2grd
COPYRIGHT
2016, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
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