xyz2grd(1) GMT xyz2grd(1)
NAME
xyz2grd - Convert data table to a grid file
SYNOPSIS
xyz2grd [ table ] -Ggrdfile
-Iincrement
-Rregion [ -A[d|f|l|m|n|r|S|s|u|z] ] [
-D[+xxname][+yyname][+zzname][+sscale][+ooffset][+ninvalid][+tti-
tle][+rremark] ] [ -S[zfile] ] [ -V[level] ] [ -Z[flags] ] [ -bibi-
nary ] [ -dinodata ] [ -eregexp ] [ -fflags ] [ -hheaders ] [ -iflags ]
[ -r ] [ -:[i|o] ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
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 num-
ber of formats, see -Z below.) Note: xyz2grd does not grid the data,
it simply reformats existing data to a grid structure. For gridding,
see surface, greenspline, nearneighbor, or triangulate.
REQUIRED ARGUMENTS
-Ggrdfile
grdfile is the name of the binary output grid file. (See GRID
FILE FORMAT below.)
-Ixinc[unit][+e|n][/yinc[unit][+e|n]]
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, nau-
tical mile or US survey foot, respectively, and will be con-
verted to the equivalent degrees longitude at the middle lati-
tude 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 coordi-
nates: If +e 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 +n to
the supplied integer argument; the increment is then recalcu-
lated from the number of nodes and the domain. The resulting
increment value depends on whether you have selected a grid-
line-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.
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
Specify the region of interest.
OPTIONAL ARGUMENTS
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.
-A[d|f|l|m|n|r|S|s|u|z]
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 or d to find the lowest (minimum) or upper (maximum)
value or the difference between the maximum and miminum value at
each node, respectively. Append m or r or S to compute mean or
RMS value or standard deviation 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.
-D[+xxname][+yyname][+zzname][+sscale][+ooffset][+ninvalid][+tti-
tle][+rremark]
Give one or more combinations for values xname, yname, zname
(give the names of those variables and in square bracket their
units, e.g., adistance [km]a), 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). Items not listed will remain untouched. Give a blank
name to completely reset a particular string. Use quotes to
group texts with more than one word. Note that for geographic
grids (-fg) xname and yname are set automatically.
-S[zfile]
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 a|)
Select verbosity level [c].
-Z[flags]
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 col-
umn 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 reg-
ular floating point values.
-bi[ncols][t] (more a|)
Select native binary input. [Default is 3 input columns]. This
option only applies to xyz input files; see -Z for z tables.
-dinodata (more a|)
Replace input columns that equal nodata with NaN. Also sets
nodes with no input xyz triplet to this value [Default is NaN].
-e[~]^<i>apattern^<i>a | -e[~]/regexp/[i] (more a|)
Only accept data records that match the given pattern.
-f[i|o]colinfo (more a|)
Specify data types of input and/or output columns.
-h[i|o][n][+c][+d][+rremark][+rtitle] (more a|)
Skip or produce header record(s). Not used with binary data.
-icols[+l][+sscale][+ooffset][,^<i>a|] (more a|)
Select input columns and transformations (0 is first column).
-r (more a|)
Set pixel node registration [gridline].
-:[i|o] (more a|)
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 just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
GRID VALUES PRECISION
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 preci-
sion once GMT operates on the grid or writes out new grids. To limit
loss of precision when processing data you should always consider nor-
malizing the data prior to processing.
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 apackinga of grids, writing out floating point
data as 1- or 2-byte integers. To specify the precision, scale and off-
set, the user should add the suffix =ID[+sscale][+ooffset][+ninvalid],
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 invalid 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 aza. 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.
GEOGRAPHICAL AND TIME COORDINATES
When the output grid type is netCDF, the coordinates will be labeled
alongitudea, alatitudea, or atimea 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.
SWAPPING LIMITATIONS
All data types can be read, even 64-bit integers, but internally grids
are stored using floats. Hence, integer values exceeding the float
typeas 23-bit mantissa may not be represented exactly. When -S is used
no grids are implied and we read data into an intermediate double con-
tainer. This means all but 64-bit integers can be represented using the
double typeas 53-bit mantissa.
EXAMPLES
To create a grid file from the ASCII data in hawaii_grv.xyz, use
gmt xyz2grd hawaii_grv.xyz -D+xdegree+ydegree+zGal+taHawaiian Grav-
itya+raGRS-80 Ellipsoid useda
-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 -D+xm+ym+zm -Graw.nc -R0/100/0/100 -I1 -V -Z -bi3f
To make a grid file from the raw binary USGS DEM (short integer scan-
line-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 -D+xm+ym+zm -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
SEE ALSO
gmt(1), grd2xyz(1), grdedit(1), grdconvert(1), greenspline(1),
nearneighbor(1), surface(1), triangulate(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 xyz2grd(1)
gmt5 5.4.2 - Generated Thu Jun 29 19:10:46 CDT 2017