.TH XYZ2GRD 1gmt "15 Jul 2011" "GMT 4.5.7" "Generic Mapping Tools"
.SH NAME
xyz2grd \- Converting an ASCII or binary table to grid file format
.SH SYNOPSIS
\fBxyz2grd\fP \fIxyzfile\fP \fB\-G\fP\fIgrdfile\fP \fB\-I\fP\fIxinc\fP[\fIunit\fP][\fB=\fP|\fB+\fP][/\fIyinc\fP[\fIunit\fP][\fB=\fP|\fB+\fP]] 
\fB\-R\fP\fIwest\fP/\fIeast\fP/\fIsouth\fP/\fInorth\fP[\fBr\fP] [ \fB\-A\fP[\fBn|z|u|l\fP] ] [ \fB\-D\fP\fIxname\fP/\fIyname\fP/\fIzname\fP/\fIscale\fP/\fIoffset\fP/\fItitle\fP/\fIremark\fP ] 
[ \fB\-E\fP[\fInodata\fP] ] [ \fB\-F\fP ] [ \fB\-H\fP[\fBi\fP][\fInrec\fP] ] [ \fB\-N\fP\fInodata\fP ] [ \fB\-S\fP[\fIzfile\fP] ] [ \fB\-V\fP ] 
[ \fB\-Z\fP[\fIflags\fP] ] [ \fB\-:\fP[\fBi\fP|\fBo\fP] ] [ \fB\-bi\fP[\fBs\fP|\fBS\fP|\fBd\fP|\fBD\fP[\fIncol\fP]|\fBc\fP[\fIvar1\fP\fB/\fP\fI...\fP]] ] [ \fB\-f\fP\fIcolinfo\fP ]
.SH DESCRIPTION
\fBxyz2grd\fP reads a z or xyz table and
creates a binary grid file.  \fBxyz2grd\fP 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 average value.  As an option (using \fB\-Z\fP),
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 \fB\-Z\fP below.)
.TP
\fI[xy]zfile\fP
ASCII [or binary] file holding z or (x,y,z) values.  xyz triplets do not
have to be sorted (for binary triplets, see \fB\-b\fP).  1-column z tables must be sorted and the \fB\-Z\fP must be set). 
.TP
\fB\-G\fP
\fIgrdfile\fP is the name of the binary output grid file.
(See GRID FILE FORMAT below.)
.TP
\fB\-I\fP
\fIx_inc\fP [and optionally \fIy_inc\fP] is the grid spacing. Optionally, append a suffix
modifier.  \fBGeographical (degrees) coordinates\fP: Append \fBm\fP to
indicate arc minutes or \fBc\fP to indicate arc seconds.  If one of the units \fBe\fP, \fBk\fP, \fBi\fP,
or \fBn\fP is appended instead, the increment is assumed to be given in meter, km, miles, or
nautical miles, respectively, and will be converted to the equivalent degrees longitude at
the middle latitude of the region (the conversion depends on \fBELLIPSOID\fP).  If /\fIy_inc\fP is given but set to 0 it will be reset equal to
\fIx_inc\fP; otherwise it will be converted to degrees latitude.  
\fBAll coordinates\fP: If \fB=\fP is appended then
the corresponding max \fIx\fP (\fIeast\fP) or \fIy\fP (\fInorth\fP) 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 \fInumber of nodes\fP desired by appending \fB+\fP 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 Appendix B for details.  Note: if \fB\-R\fP\fIgrdfile\fP is used then
grid spacing has already been initialized; use \fB\-I\fP to override the values.
.TP
\fB\-R\fP
\fIxmin\fP, \fIxmax\fP, \fIymin\fP, and \fIymax\fP specify the Region of interest.  For geographic
regions, these limits correspond to \fIwest, east, south,\fP and \fInorth\fP and you may specify them
in decimal degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format.  Append \fBr\fP if lower left and upper right
map coordinates are given instead of w/e/s/n.  The two shorthands \fB\-Rg\fP and \fB\-Rd\fP stand for global domain
(0/360 and -180/+180 in longitude respectively, with -90/+90 in latitude).  Alternatively, specify the name
of an existing grid file and the \fB\-R\fP settings (and grid spacing, if applicable) are copied from the grid.
For calendar time coordinates you may either give (a) relative
time (relative to the selected \fBTIME_EPOCH\fP and in the selected \fBTIME_UNIT\fP; append \fBt\fP to
\fB\-JX\fP|\fBx\fP), or (b) absolute time of the form [\fIdate\fP]\fBT\fP[\fIclock\fP]
(append \fBT\fP to \fB\-JX\fP|\fBx\fP).  At least one of \fIdate\fP and \fIclock\fP
must be present; the \fBT\fP is always required.  The \fIdate\fP string must be of the form [-]yyyy[-mm[-dd]]
(Gregorian calendar) or yyyy[-Www[-d]] (ISO week calendar), while the \fIclock\fP string must be of
the form hh:mm:ss[.xxx].  The use of delimiters and their type and positions must be exactly as indicated
(however, input, output and plot formats are customizable; see \fBgmtdefaults\fP). 
.SH OPTIONS
.TP
\fB\-A\fP
Add up multiple values that belong to the same node (same as \fB\-Az\fP).
Append \fBn\fP to simply count the number of data points that were assigned to each node.
Append \fBl\fP or \fBu\fP to find the lowest (minimum) or upper (maximum) value at each node, respectively. 
[Default (no \fB\-A\fP option) will calculate mean value].  Ignored if \fB\-Z\fP is given.
.TP
\fB\-D\fP
Give values for \fIxname, yname, zname, scale, offset, title,\fP and \fIremark\fP.
To leave some of these values untouched, specify = as the value.
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:
\fB\-D\fP:\fIxname\fP:\fIyname\fP:\fIzname\fP:\fIscale\fP:\fIoffset\fP:\fItitle\fP:\fIremark\fP:
.TP
\fB\-E\fP
Convert an ESRI ArcInfo ASCII interchange grid format file to a \fBGMT\fP grid.  Append \fInodata\fP which is a data
value that should be set to NaN in the grid [If we find the optional 6th record in the file we will use it instead].
The values normally given by \fB\-R\fP, \fB\-I\fP, and \fB\-F\fP are determined from the ESRI header instead.
.TP
\fB\-F\fP
Force pixel node registration [Default is gridline registration].
(Node registrations are defined in \fBGMT\fP Cookbook Appendix B on grid file formats.)
.TP
\fB\-H\fP
Input file(s) has header record(s).  If used, the default number of header records is \fBN_HEADER_RECS\fP.
Use \fB\-Hi\fP if only input data should have header records [Default will write out header records if the
input data have them]. Blank lines and lines starting with # are always skipped.
Not used with binary data.
.TP
\fB\-N\fP
No data.  Set nodes with no input xyz triplet to this value [Default is NaN].  For z-tables, this
option is used to replace z-values that equal \fInodata\fP with NaN.
.TP
\fB\-S\fP
Swap the byte-order of the input only.  No grid file is produced.  You must
also supply the \fB\-Z\fP option.  The output is written to \fIzfile\fP (or
stdout if not supplied).
.TP
\fB\-V\fP
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
.TP
\fB\-Z\fP
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 \fIflags\fP.
If incoming data represents rows, make \fIflags\fP start with \fBT\fP(op) if first row is y = ymax
or \fBB\fP(ottom) if first row is y = ymin.  Then, append \fBL\fP or \fBR\fP to indicate that first element is at left
or right end of row.  Likewise for column formats: start with \fBL\fP or \fBR\fP to position first column,
and then append \fBT\fP or \fBB\fP to position first element in a row.  
For gridline registered grids:  If data are periodic in x but the
incoming data do not contain the (redundant) column at x = xmax, append \fBx\fP.  For data periodic in y
without redundant row at y = ymax, append \fBy\fP.  Append \fBs\fP\fIn\fP to skip the first \fIn\fP number
of bytes (probably a header).  If the byte-order needs to be swapped, append \fBw\fP.  Select
one of several data types (all binary except \fBa\fP):
.br
.sp
	\fBA\fP  ASCII representation of one or more floating point values per record
.sp
	\fBa\fP  ASCII representation of a single item per record
.br
	\fBc\fP  signed 1-byte character
.br
	\fBu\fP  unsigned 1-byte character
.br
	\fBh\fP  short 2-byte integer
.br
	\fBi\fP  4-byte integer
.br
	\fBl\fP  long (4- or 8-byte) integer [architecture-dependent!]
.br
	\fBf\fP  4-byte floating point single precision
.br
	\fBd\fP  8-byte floating point double precision
.br
.sp
Default format is scanline orientation of ASCII numbers: \fB\-ZTLa\fP.
Note that \fB\-Z\fP only applies to 1-column input.  The difference between \fBA\fP and \fBa\fP is that
the latter can decode both \fIdate\fPT\fIclock\fP and \fIddd:mm:ss[.xx]\fP formats while the former is
strictly for regular floating point values.
.TP
\fB\-:\fP
Toggles between (longitude,latitude) and (latitude,longitude) input and/or output.  [Default is (longitude,latitude)].
Append \fBi\fP to select input only or \fBo\fP to select output only.  [Default affects both].
.TP
\fB\-bi\fP
Selects binary input.
Append \fBs\fP for single precision [Default is \fBd\fP (double)].
Uppercase \fBS\fP or \fBD\fP will force byte-swapping.
Optionally, append \fIncol\fP, the number of columns in your binary input file
if it exceeds the columns needed by the program.
Or append \fBc\fP if the input file is netCDF. Optionally, append \fIvar1\fP\fB/\fP\fIvar2\fP\fB/\fP\fI...\fP to
specify the variables to be read.
[Default is 3 input columns].  This option only applies to xyz input files; see \fB\-Z\fP for z tables.
.TP
\fB\-f\fP
Special formatting of input and/or output columns (time or geographical data).
Specify \fBi\fP or \fBo\fP to make this apply only to input or output [Default applies to both].
Give one or more columns (or column ranges) separated by commas.
Append \fBT\fP (absolute calendar time), \fBt\fP (relative time in chosen \fBTIME_UNIT\fP since \fBTIME_EPOCH\fP),
\fBx\fP (longitude), \fBy\fP (latitude), or \fBf\fP (floating point) to each column
or column range item.  Shorthand \fB\-f\fP[\fBi\fP|\fBo\fP]\fBg\fP means \fB\-f\fP[\fBi\fP|\fBo\fP]0\fBx\fP,1\fBy\fP
(geographic coordinates).
.SH 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 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 processing.
.SH GRID FILE FORMATS
By default \fBGMT\fP writes out grid as single precision floats in a COARDS-complaint netCDF file format.
However, \fBGMT\fP 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 2- or 4-byte integers. To specify the precision, scale and offset, the user should add the suffix
\fB=\fP\fIid\fP[\fB/\fP\fIscale\fP\fB/\fP\fIoffset\fP[\fB/\fP\fInan\fP]], where \fIid\fP is a two-letter identifier of the grid type and precision, and \fIscale\fP and \fIoffset\fP are optional scale factor
and offset to be applied to all grid values, and \fInan\fP is the value used to indicate missing data.
See \fBgrdreformat\fP(1) and Section 4.17 of the GMT Technical Reference and Cookbook for more information.
.P
When writing a netCDF file, the grid is stored by default with the variable name "z". To specify another variable name \fIvarname\fP,
append \fB?\fP\fIvarname\fP to the file name.  Note that you may need to escape the special meaning of \fB?\fP in your shell program
by putting a backslash in front of it, or by placing the filename and suffix between quotes or double quotes.
.SH 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
\fB\-f\fP or \fB\-R\fP options. For example, both \fB\-f0x\fP \fB\-f1t\fP and \fB\-R\fP90w/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 \fBTIME_UNIT\fP and \fBTIME_EPOCH\fP in the \.gmtdefaults file or on the command line.
In addition, the \fBunit\fP attribute of the time variable will indicate both this unit and epoch.
.SH EXAMPLES
To create a grid file from the ASCII data in hawaii_grv.xyz, use
.br
.sp
\fBxyz2grd\fP hawaii_grv.xyz \fB\-D\fPdegree/degree/mGal/1/0/"Hawaiian Gravity"/"GRS-80 Ellipsoid used"
\fB\-G\fPhawaii_grv_new.grd \fB\-R\fP198/208/18/25 \fB\-I\fP5\fBm\fP \fB\-V\fP
.br
.sp
To create a grid file from the raw binary (3-column, single-precision) scanline-oriented data raw.b, use
.br
.sp
\fBxyz2grd\fP raw.b \fB\-D\fPm/m/m/1/0/=/= \fB\-G\fPraw.grd \fB\-R\fP0/100/0/100 \fB\-I\fP1 \fB\-V\fP \fB\-Z\fP \fB\-b\fP3
.br
.sp
To make a grid file from the raw binary USGS DEM (short integer) scanline-oriented data topo30. 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
.br
.sp
\fBxyz2grd\fP topo30. \fB\-D\fPm/m/m/1/0/=/= \fB\-G\fPustopo.grd \fB\-R\fP234/294/24/50 \fB\-I\fP30c \fB\-N\fP-9999 \fB\-B\fP \fB\-ZTLhw\fP
.br
.sp
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
.br
.sp
\fBxyz2grd\fP floats.bin \fB\-S\fPnew_floats.bin \fB\-V\fP \fB\-Zf\fP
.SH "SEE ALSO"
.IR GMT (1),
.IR grd2xyz (1),
.IR grdedit (1)