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xyz2grd - Convert data table to a grid file


xyz2grd [ table ] grdfile increment region [ [f|l|m|n|r|s|u|z] ] [
xname/yname/zname/scale/offset/invalid/title/remark ] [ [zfile] ] [ [level] ] [ [flags] ]
[ -bi<binary> ] [ -di<nodata> ] [ -f<flags> ] [ -h<headers> ] [ -i<flags> ] [ -r ] [
-:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.


xyz2grd reads one or more z or xyz tables and creates a binary grid file. xyz2grd will
report if some of the nodes are not filled in with data. Such unconstrained nodes are set
to a value specified by the user [Default is NaN]. Nodes with more than one value will be
set to the mean value. As an option (using -Z), a 1-column z-table may be read assuming
all nodes are present (z-tables can be in organized in a number of formats, see -Z below.)


grdfile is the name of the binary output grid file. (See GRID FILE FORMAT below.)

x_inc [and optionally y_inc] is the grid spacing. Optionally, append a suffix
modifier. Geographical (degrees) coordinates: Append m to indicate arc minutes or s
to indicate arc seconds. If one of the units e, f, k, M, n or u is appended
instead, the increment is assumed to be given in meter, foot, km, Mile, nautical
mile or US survey foot, respectively, and will be converted to the equivalent
degrees longitude at the middle latitude of the region (the conversion depends on
PROJ_ELLIPSOID). If /y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordinates: If = is
appended then the corresponding max x (east) or y (north) may be slightly adjusted
to fit exactly the given increment [by default the increment may be adjusted
slightly to fit the given domain]. Finally, instead of giving an increment you may
specify the number of nodes desired by appending + to the supplied integer
argument; the increment is then recalculated from the number of nodes and the
domain. The resulting increment value depends on whether you have selected a
gridline-registered or pixel-registered grid; see App-file-formats for details.
Note: if -Rgrdfile is used then the grid spacing has already been initialized; use
-I to override the values.

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.


table One or more ASCII [or binary, see -bi] files holding z or (x,y,z) values. The xyz
triplets do not have to be sorted. One-column z tables must be sorted and the -Z
must be set.

By default we will calculate mean values if multiple entries fall on the same node.
Use -A to change this behavior, except it is ignored if -Z is given. Append f or s
to simply keep the first or last data point that was assigned to each node. Append
l or u to find the lowest (minimum) or upper (maximum) value at each node,
respectively. Append m or r to compute mean or RMS value at each node,
respectively. Append n to simply count the number of data points that were assigned
to each node (this only requires two input columns x and y as z is not consulted).
Append z to sum multiple values that belong to the same node.

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.

Swap the byte-order of the input only. No grid file is produced. You must also
supply the -Z option. The output is written to zfile (or stdout if not supplied).

-V[level] (more ...)
Select verbosity level [c].

Read a 1-column ASCII [or binary] table. This assumes that all the nodes are
present and sorted according to specified ordering convention contained in flags.
If incoming data represents rows, make flags start with T(op) if first row is y =
ymax or B(ottom) if first row is y = ymin. Then, append L or R to indicate that
first element is at left or right end of row. Likewise for column formats: start
with L or R to position first column, and then append T or B to position first
element in a row. Note: These two row/column indicators are only required for
grids; for other tables they do not apply. For gridline registered grids: If data
are periodic in x but the incoming data do not contain the (redundant) column at x
= xmax, append x. For data periodic in y without redundant row at y = ymax, append
y. Append sn to skip the first n number of bytes (probably a header). If the
byte-order or the words needs to be swapped, append w. Select one of several data
types (all binary except a):

A ASCII representation of one or more floating point values per record

a ASCII representation of a single item per record

c int8_t, signed 1-byte character

u uint8_t, unsigned 1-byte character

h int16_t, signed 2-byte integer

H uint16_t, unsigned 2-byte integer

i int32_t, signed 4-byte integer

I uint32_t, unsigned 4-byte integer

l int64_t, long (8-byte) integer

L uint64_t, unsigned long (8-byte) integer

f 4-byte floating point single precision

d 8-byte floating point double precision

Default format is scanline orientation of ASCII numbers: -ZTLa. Note that -Z only
applies to 1-column input. The difference between A and a is that the latter can
decode both dateTclock and ddd:mm:ss[.xx] formats while the former is strictly for
regular floating point values.

-bi[ncols][t] (more ...)
Select native binary input. [Default is 3 input columns]. This option only applies
to xyz input files; see -Z for z tables.

-dinodata (more ...)
Replace input columns that equal nodata with NaN. Also sets nodes with no input xyz
triplet to this value [Default is 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). Not used with binary data.

-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).

-r (more ...)
Set pixel node registration [gridline].

-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.

-^ 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

Print GMT version and exit.

Print full path to GMT share directory and exit.


Regardless of the precision of the input data, GMT programs that create grid files will
internally hold the grids in 4-byte floating point arrays. This is done to conserve memory
and furthermore most if not all real data can be stored using 4-byte floating point
values. Data with higher precision (i.e., double precision values) will lose that
precision once GMT operates on the grid or writes out new grids. To limit loss of
precision when processing data you should always consider normalizing the data prior to


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. To specify the precision, scale and offset, the user should
add the suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of the grid
type and precision, and scale and offset are optional scale factor and offset to be
applied to all grid values, and nan is the value used to indicate missing data. See
grdconvert and Section grid-file-format of the GMT Technical Reference and Cookbook for
more information.

When writing a netCDF file, the grid is stored by default with the variable name "z". To
specify another variable name varname, append ?varname to the file name. Note that you may
need to escape the special meaning of ? in your shell program by putting a backslash in
front of it, or by placing the filename and suffix between quotes or double quotes.


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.


All data types can be read, even 64-bit integers, but internally grids are stored using
floats. Hence, integer values exceeding the float type's 23-bit mantissa may not be
represented exactly. When -S is used no grids are implied and we read data into an
intermediate double container. This means all but 64-bit integers can be represented using
the double type's 53-bit mantissa.


To create a grid file from the ASCII data in hawaii_grv.xyz, use

gmt xyz2grd hawaii_grv.xyz -Ddegree/degree/mGal/1/0//"Hawaiian Gravity"/"GRS-80
Ellipsoid used"
-Ghawaii_grv_new.nc -R198/208/18/25 -I5m -V

To create a grid file from the raw binary (3-column, single-precision scanline-oriented
data raw.b, use
gmt xyz2grd raw.b -Dm/m/m/1/0 -Graw.nc -R0/100/0/100 -I1 -V -Z -bi3f

To make a grid file from the raw binary USGS DEM (short integer scanline-oriented data
topo30.b on the NGDC global relief Data CD-ROM, with values of -9999 indicate missing
data, one must on some machine reverse the byte-order. On such machines (like Sun), use
gmt xyz2grd topo30.b -Dm/m/m/1/0 -Gustopo.nc -R234/294/24/50 -I30s -di-9999 -ZTLhw

Say you have received a binary file with 4-byte floating points that were written on a
machine of different byte-order than yours. You can swap the byte-order with
gmt xyz2grd floats.bin -Snew_floats.bin -V -Zf

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