GRDEDIT

grdedit − Modifying the header in a 2-D grdfile

grdedit grdfile [ −A ] [ −Dxname/yname/zname/scale/offset/title/remark ] [ −Nxyzfile ] [ −Rwest/east/south/north[r] ] [ −S ] [ −T ] [ −V ] [ −:[i|o] ] [ −bi[s|S|d|D][ncol] ] [ −f[i|o]colinfo ]

grdedit reads the header information in a binary 2-D grdfile 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 grdheader.

No space between the option flag and the associated arguments. Use upper case for the option flags and lower case for modifiers.

grdfile

Name of the 2-D grdfile to modify

−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 gridfiles (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.

−D

Give new values for xname, yname, zname, scale, offset, title, and remark. To leave some of the values untouched, specify = as the new value.

−H

Input file(s) has Header record(s). Number of header records can be changed by editing your .gmtdefaults4 file. If used, GMT default is 1 header record. Use −Hi if only input data should have header records [Default will write out header records if the input data have them].

−N

Read the ASCII (or binary; see −bi) file xyzfile and replace the corresponding nodal values in the grid with these z values.

−R

xmin, xmax, ymin, and ymax specify the Region of interest. For geographic regions, these limits correspond to west, east, south, and north and you may specify them in decimal degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and upper right map coordinates are given instead of wesn. The two shorthands −Rg −Rd stand for global domain (0/360 or -180/+180 in longitude respectively, with -90/+90 in latitude). For calendar time coordinates you may either give relative time (relative to the selected TIME_EPOCH and in the selected TIME_UNIT; append t to −JX|x), or absolute time of the form [date]T[clock] (append T to −JX|x). At least one of date and clock must be present; the T is always required. The date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock string must be of the form hh:mm:ss[.xxx]. The use of delimiters and their type and positions must be as indicated (however, input/output and plotting formats are flexible). 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 longitudionally according to the new borders given in −R.

−T

Make necessary changes in the header to convert a gridline-registred 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

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

−bi

Selects binary input. Append s for single precision [Default is d (double)]. Uppercase S (or D) will force byte-swapping. Optionally, append ncol, the number of columns in your binary file if it exceeds the columns needed by the program. [Default is 3 input columns].

−f

Special formatting of input and output columns (time or geographical data). Specify i(nput) or o(utput) [Default is both input and output]. Give one or more columns (or column ranges) separated by commas. Append T (Absolute calendar time), t (time relative to chosen TIME_EPOCH), x (longitude), y (latitude), or f (floating point) to each column or column range item. Shorthand −f[i|o]g means −f[i|o]0x,1y (geographic coordinates).

Let us assume the file data.grd 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

grdedit data.grd −R-60/-50/10/30 −D=/=/=/=/=/"Gravity Anomalies"/=

The grid world.grd has the limits 0/360/-72/72. To shift the data so that the limits would be -180/180/-72/72, use

grdedit world.grd −R-180/180/-72/72 −S

The file junk.grd was created prior to GMT 3.1 with incompatible −R and −I arguments. To reset the x- and y-increments we run

grdedit junk.grd −A

GMT(l), grd2xyz(l), xyz2grd(l)