1XYZ2GRD(1) Generic Mapping Tools XYZ2GRD(1)
2
6 xyz2grd - Converting an ASCII or binary table to grid file format
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9 xyz2grd xyzfile -Ggrdfile -Ixinc[unit][=|+][/yinc[unit][=|+]]
10 -Rwest/east/south/north[r] [ -A[n|z|u|l] ] [
11 -Dxname/yname/zname/scale/offset/title/remark ] [ -E[nodata] ] [ -F ] [
12 -H[i][nrec] ] [ -Nnodata ] [ -S[zfile] ] [ -V ] [ -Z[flags] ] [ -:[i|o]
13 ] [ -bi[s|S|d|D[ncol]|c[var1/...]] ] [ -fcolinfo ]
14
16 xyz2grd reads a z or xyz table and creates a binary grid file. xyz2grd
17 will report if some of the nodes are not filled in with data. Such
18 unconstrained nodes are set to a value specified by the user [Default
19 is NaN]. Nodes with more than one value will be set to the average
20 value. As an option (using -Z), a 1-column z-table may be read assum‐
21 ing all nodes are present (z-tables can be in organized in a number of
22 formats, see -Z below.)
23 [xy]zfile
25 ASCII [or binary] file holding z or (x,y,z) values. xyz
26 triplets do not have to be sorted (for binary triplets, see -b).
27 1-column z tables must be sorted and the -Z must be set).
28 -G grdfile is the name of the binary output grid file. (See GRID
30 FILE FORMAT below.)
31 -I x_inc [and optionally y_inc] is the grid spacing. Optionally,
33 append a suffix modifier. Geographical (degrees) coordinates:
34 Append m to indicate arc minutes or c to indicate arc seconds.
35 If one of the units e, k, i, or n is appended instead, the
36 increment is assumed to be given in meter, km, miles, or nauti‐
37 cal miles, respectively, and will be converted to the equivalent
38 degrees longitude at the middle latitude of the region (the con‐
39 version depends on ELLIPSOID). If /y_inc is given but set to 0
40 it will be reset equal to x_inc; otherwise it will be converted
41 to degrees latitude. All coordinates: If = is appended then the
42 corresponding max x (east) or y (north) may be slightly adjusted
43 to fit exactly the given increment [by default the increment may
44 be adjusted slightly to fit the given domain]. Finally, instead
45 of giving an increment you may specify the number of nodes
46 desired by appending + to the supplied integer argument; the
47 increment is then recalculated from the number of nodes and the
48 domain. The resulting increment value depends on whether you
49 have selected a gridline-registered or pixel-registered grid;
50 see Appendix B for details.
51 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
53 geographic regions, these limits correspond to west, east,
54 south, and north and you may specify them in decimal degrees or
55 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
56 and upper right map coordinates are given instead of w/e/s/n.
57 The two shorthands -Rg and -Rd stand for global domain (0/360
58 and -180/+180 in longitude respectively, with -90/+90 in lati‐
59 tude). For calendar time coordinates you may either give (a)
60 relative time (relative to the selected TIME_EPOCH and in the
61 selected TIME_UNIT; append t to -JX|x), or (b) absolute time of
62 the form [date]T[clock] (append T to -JX|x). At least one of
63 date and clock must be present; the T is always required. The
64 date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
65 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
66 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
67 iters and their type and positions must be exactly as indicated
68 (however, input, output and plot formats are customizable; see
69 gmtdefaults).
70
72 -A Add up multiple values that belong to the same node (same as
73 -Az). Append n to simply count the number of data points that
74 were assigned to each node. Append l or u to find the lowest
75 (minimum) or upper (maximum) value at each node, respectively.
76 [Default (no -A option) will calculate mean value]. Ignored if
77 -Z is given.
78 -D Give values for xname, yname, zname, scale, offset, title, and
80 remark. To leave some of these values untouched, specify = as
81 the value. Alternatively, to allow "/" to be part of one of the
82 values, use any non-alphanumeric character (and not the equal
83 sign) as separator by both starting and ending with it. For
84 example: -D:xname:yname:zname:scale:offset:title:remark:
85 -E Convert an ESRI ArcInfo ASCII interchange grid format file to a
87 GMT grid. Append nodata which is a data value that should be
88 set to NaN in the grid [Default is to read the optional 6th
89 record in the file and get nodata]. The values normally given
90 by -R, -I, and -F are determined from the ESRI header instead.
91 -F Force pixel node registration [Default is gridline registra‐
93 tion]. (Node registrations are defined in GMT Cookbook Appendix
94 B on grid file formats.)
95 -H Input file(s) has Header record(s). Number of header records
97 can be changed by editing your .gmtdefaults4 file. If used, GMT
98 default is 1 header record. Use -Hi if only input data should
99 have header records [Default will write out header records if
100 the input data have them]. Blank lines and lines starting with #
101 are always skipped. Not used with binary data.
102 -N No data. Set nodes with no input xyz triplet to this value
104 [Default is NaN]. For z-tables, this option is used to replace
105 z-values that equal nodata with NaN.
106 -S Swap the byte-order of the input only. No grid file is pro‐
108 duced. You must also supply the -Z option. The output is writ‐
109 ten to zfile (or stdout if not supplied).
110 -V Selects verbose mode, which will send progress reports to stderr
112 [Default runs "silently"].
113 -Z Read a 1-column ASCII [or binary] table. This assumes that all
115 the nodes are present and sorted according to specified ordering
116 convention contained in flags. If incoming data represents
117 rows, make flags start with T(op) if first row is y = ymax or
118 B(ottom) if first row is y = ymin. Then, append L or R to indi‐
119 cate that first element is at left or right end of row. Like‐
120 wise for column formats: start with L or R to position first
121 column, and then append T or B to position first element in a
122 row. For gridline registered grids: If data are periodic in x
123 but the incoming data do not contain the (redundant) column at x
124 = xmax, append x. For data periodic in y without redundant row
125 at y = ymax, append y. Append sn to skip the first n number of
126 bytes (probably a header). If the byte-order needs to be
127 swapped, append w. Select one of several data types (all binary
128 except a):
129 a ASCII representation
131 c signed 1-byte character
132 u unsigned 1-byte character
133 h short 2-byte integer
134 i 4-byte integer
135 l long (4- or 8-byte) integer [architecture-dependent!]
136 f 4-byte floating point single precision
137 d 8-byte floating point double precision
138 Default format is scanline orientation of ASCII numbers: -ZTLa.
140 Note that -Z only applies to 1-column input.
141 -: Toggles between (longitude,latitude) and (latitude,longitude)
143 input and/or output. [Default is (longitude,latitude)]. Append
144 i to select input only or o to select output only. [Default
145 affects both].
146 -bi Selects binary input. Append s for single precision [Default is
148 d (double)]. Uppercase S or D will force byte-swapping.
149 Optionally, append ncol, the number of columns in your binary
150 input file if it exceeds the columns needed by the program. Or
151 append c if the input file is netCDF. Optionally, append
152 var1/var2/... to specify the variables to be read. [Default is
153 3 input columns]. This option only applies to xyz input files;
154 see -Z for z tables.
155 -f Special formatting of input and/or output columns (time or geo‐
157 graphical data). Specify i or o to make this apply only to
158 input or output [Default applies to both]. Give one or more
159 columns (or column ranges) separated by commas. Append T (abso‐
160 lute calendar time), t (relative time in chosen TIME_UNIT since
161 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
162 to each column or column range item. Shorthand -f[i|o]g means
163 -f[i|o]0x,1y (geographic coordinates).
164
166 Regardless of the precision of the input data, GMT programs that create
167 gridded files will internally hold the grids in 4-byte floating point
168 arrays. This is done to conserve memory and futhermore most if not all
169 real data can be stored using 4-byte floating point values. Data with
170 higher precision (i.e., double precision values) will lose that preci‐
171 sion once GMT operates on the grid or writes out new grids. To limit
172 loss of precision when processing data you should always consider nor‐
173 malizing the data prior to processing.
174
176 By default GMT writes out grid as single precision floats in a COARDS-
177 complaint netCDF file format. However, GMT is able to produce grid
178 files in many other commonly used grid file formats and also facili‐
179 tates so called "packing" of grids, writing out floating point data as
180 2- or 4-byte integers. To specify the precision, scale and offset, the
181 user should add the suffix =id[/scale/offset[/nan]], where id is a two-
182 letter identifier of the grid type and precision, and scale and offset
183 are optional scale factor and offset to be applied to all grid values,
184 and nan is the value used to indicate missing data. See grdreformat(1)
185 and Section 4.17 of the GMT Technical Reference and Cookbook for more
186 information.
187 When writing a netCDF file, the grid is stored by default with the
189 variable name "z". To specify another variable name varname, append
190 ?varname to the file name. Note that you may need to escape the spe‐
191 cial meaning of ? in your shell program by putting a backslash in front
192 of it, or by placing the filename and suffix between quotes or double
193 quotes.
194
196 When the output grid type is netCDF, the coordinates will be labeled
197 "longitude", "latitude", or "time" based on the attributes of the input
198 data or grid (if any) or on the -f or -R options. For example, both
199 -f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid.
200 When the x, y, or z coordinate is time, it will be stored in the grid
201 as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH
202 in the .gmtdefaults file or on the command line. In addition, the unit
203 attribute of the time variable will indicate both this unit and epoch.
204
206 To create a grid file from the ASCII data in hawaii_grv.xyz, use
207 xyz2grd hawaii_grv.xyz -Ddegree/degree/mGal/1/0/"Hawaiian Grav‐
209 ity"/"GRS-80 Ellipsoid used" -Ghawaii_grv_new.grd -R198/208/18/25 -I5m
210 -V
211 To create a grid file from the raw binary (3-column, single-precision)
213 scanline-oriented data raw.b, use
214 xyz2grd raw.b -Dm/m/m/1/0/=/= -Graw.grd -R0/100/0/100 -I1 -V -Z -b3
216 To make a grid file from the raw binary USGS DEM (short integer) scan‐
218 line-oriented data topo30. on the NGDC global relief Data CD-ROM, with
219 values of -9999 indicate missing data, one must on some machine reverse
220 the byte-order. On such machines (like Sun), use
221 xyz2grd topo30. -Dm/m/m/1/0/=/= -Gustopo.grd -R234/294/24/50 -I30c
223 -N-9999 -V -ZTLhw
224 Say you have received a binary file with 4-byte floating points that
226 were written on a machine of different byte-order than yours. You can
227 swap the byte-order with
228 xyz2grd floats.bin -Snew_floats.bin -V -Zf
230
232 GMT(1), grd2xyz(1), grdedit(1)
233GMT 4.3.1 15 May 2008 XYZ2GRD(1)