1XYZ2GRD(1) Generic Mapping Tools XYZ2GRD(1)
2
6 xyz2grd - Converting an ASCII or binary table to grid file format
7
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. Note: if -Rgrdfile is used then
51 grid spacing has already been initialized; use -I to override
52 the values.
53 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
55 geographic regions, these limits correspond to west, east,
56 south, and north and you may specify them in decimal degrees or
57 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
58 and upper right map coordinates are given instead of w/e/s/n.
59 The two shorthands -Rg and -Rd stand for global domain (0/360
60 and -180/+180 in longitude respectively, with -90/+90 in lati‐
61 tude). Alternatively, specify the name of an existing grid file
62 and the -R settings (and grid spacing, if applicable) are copied
63 from the grid. For calendar time coordinates you may either
64 give (a) relative time (relative to the selected TIME_EPOCH and
65 in the selected TIME_UNIT; append t to -JX|x), or (b) absolute
66 time of the form [date]T[clock] (append T to -JX|x). At least
67 one of date and clock must be present; the T is always required.
68 The date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
69 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
70 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
71 iters and their type and positions must be exactly as indicated
72 (however, input, output and plot formats are customizable; see
73 gmtdefaults).
74
76 -A Add up multiple values that belong to the same node (same as
77 -Az). Append n to simply count the number of data points that
78 were assigned to each node. Append l or u to find the lowest
79 (minimum) or upper (maximum) value at each node, respectively.
80 [Default (no -A option) will calculate mean value]. Ignored if
81 -Z is given.
82 -D Give values for xname, yname, zname, scale, offset, title, and
84 remark. To leave some of these values untouched, specify = as
85 the value. Alternatively, to allow "/" to be part of one of the
86 values, use any non-alphanumeric character (and not the equal
87 sign) as separator by both starting and ending with it. For
88 example: -D:xname:yname:zname:scale:offset:title:remark:
89 -E Convert an ESRI ArcInfo ASCII interchange grid format file to a
91 GMT grid. Append nodata which is a data value that should be
92 set to NaN in the grid [If we find the optional 6th record in
93 the file we will use it instead]. The values normally given by
94 -R, -I, and -F are determined from the ESRI header instead.
95 -F Force pixel node registration [Default is gridline registra‐
97 tion]. (Node registrations are defined in GMT Cookbook Appendix
98 B on grid file formats.)
99 -H Input file(s) has header record(s). If used, the default number
101 of header records is N_HEADER_RECS. Use -Hi if only input data
102 should have header records [Default will write out header
103 records if the input data have them]. Blank lines and lines
104 starting with # are always skipped. Not used with binary data.
105 -N No data. Set nodes with no input xyz triplet to this value
107 [Default is NaN]. For z-tables, this option is used to replace
108 z-values that equal nodata with NaN.
109 -S Swap the byte-order of the input only. No grid file is pro‐
111 duced. You must also supply the -Z option. The output is writ‐
112 ten to zfile (or stdout if not supplied).
113 -V Selects verbose mode, which will send progress reports to stderr
115 [Default runs "silently"].
116 -Z Read a 1-column ASCII [or binary] table. This assumes that all
118 the nodes are present and sorted according to specified ordering
119 convention contained in flags. If incoming data represents
120 rows, make flags start with T(op) if first row is y = ymax or
121 B(ottom) if first row is y = ymin. Then, append L or R to indi‐
122 cate that first element is at left or right end of row. Like‐
123 wise for column formats: start with L or R to position first
124 column, and then append T or B to position first element in a
125 row. For gridline registered grids: If data are periodic in x
126 but the incoming data do not contain the (redundant) column at x
127 = xmax, append x. For data periodic in y without redundant row
128 at y = ymax, append y. Append sn to skip the first n number of
129 bytes (probably a header). If the byte-order needs to be
130 swapped, append w. Select one of several data types (all binary
131 except a):
132 A ASCII representation of one or more floating point val‐
134 ues per record
135 a ASCII representation of a single item per record
137 c signed 1-byte character
138 u unsigned 1-byte character
139 h short 2-byte integer
140 i 4-byte integer
141 l long (4- or 8-byte) integer [architecture-dependent!]
142 f 4-byte floating point single precision
143 d 8-byte floating point double precision
144 Default format is scanline orientation of ASCII numbers: -ZTLa.
146 Note that -Z only applies to 1-column input. The difference
147 between A and a is that the latter can decode both dateTclock
148 and ddd:mm:ss[.xx] formats while the former is strictly for reg‐
149 ular floating point values.
150 -: Toggles between (longitude,latitude) and (latitude,longitude)
152 input and/or output. [Default is (longitude,latitude)]. Append
153 i to select input only or o to select output only. [Default
154 affects both].
155 -bi Selects binary input. Append s for single precision [Default is
157 d (double)]. Uppercase S or D will force byte-swapping.
158 Optionally, append ncol, the number of columns in your binary
159 input file if it exceeds the columns needed by the program. Or
160 append c if the input file is netCDF. Optionally, append
161 var1/var2/... to specify the variables to be read. [Default is
162 3 input columns]. This option only applies to xyz input files;
163 see -Z for z tables.
164 -f Special formatting of input and/or output columns (time or geo‐
166 graphical data). Specify i or o to make this apply only to
167 input or output [Default applies to both]. Give one or more
168 columns (or column ranges) separated by commas. Append T (abso‐
169 lute calendar time), t (relative time in chosen TIME_UNIT since
170 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
171 to each column or column range item. Shorthand -f[i|o]g means
172 -f[i|o]0x,1y (geographic coordinates).
173
175 Regardless of the precision of the input data, GMT programs that create
176 grid files will internally hold the grids in 4-byte floating point
177 arrays. This is done to conserve memory and furthermore most if not
178 all real data can be stored using 4-byte floating point values. Data
179 with higher precision (i.e., double precision values) will lose that
180 precision once GMT operates on the grid or writes out new grids. To
181 limit loss of precision when processing data you should always consider
182 normalizing the data prior to processing.
183
185 By default GMT writes out grid as single precision floats in a COARDS-
186 complaint netCDF file format. However, GMT is able to produce grid
187 files in many other commonly used grid file formats and also facili‐
188 tates so called "packing" of grids, writing out floating point data as
189 2- or 4-byte integers. To specify the precision, scale and offset, the
190 user should add the suffix =id[/scale/offset[/nan]], where id is a two-
191 letter identifier of the grid type and precision, and scale and offset
192 are optional scale factor and offset to be applied to all grid values,
193 and nan is the value used to indicate missing data. See grdreformat(1)
194 and Section 4.17 of the GMT Technical Reference and Cookbook for more
195 information.
196 When writing a netCDF file, the grid is stored by default with the
198 variable name "z". To specify another variable name varname, append
199 ?varname to the file name. Note that you may need to escape the spe‐
200 cial meaning of ? in your shell program by putting a backslash in front
201 of it, or by placing the filename and suffix between quotes or double
202 quotes.
203
205 When the output grid type is netCDF, the coordinates will be labeled
206 "longitude", "latitude", or "time" based on the attributes of the input
207 data or grid (if any) or on the -f or -R options. For example, both
208 -f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid.
209 When the x, y, or z coordinate is time, it will be stored in the grid
210 as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH
211 in the .gmtdefaults file or on the command line. In addition, the unit
212 attribute of the time variable will indicate both this unit and epoch.
213
215 To create a grid file from the ASCII data in hawaii_grv.xyz, use
216 xyz2grd hawaii_grv.xyz -Ddegree/degree/mGal/1/0/"Hawaiian Grav‐
218 ity"/"GRS-80 Ellipsoid used" -Ghawaii_grv_new.grd -R198/208/18/25 -I5m
219 -V
220 To create a grid file from the raw binary (3-column, single-precision)
222 scanline-oriented data raw.b, use
223 xyz2grd raw.b -Dm/m/m/1/0/=/= -Graw.grd -R0/100/0/100 -I1 -V -Z -b3
225 To make a grid file from the raw binary USGS DEM (short integer) scan‐
227 line-oriented data topo30. on the NGDC global relief Data CD-ROM, with
228 values of -9999 indicate missing data, one must on some machine reverse
229 the byte-order. On such machines (like Sun), use
230 xyz2grd topo30. -Dm/m/m/1/0/=/= -Gustopo.grd -R234/294/24/50 -I30c
232 -N-9999 -B -ZTLhw
233 Say you have received a binary file with 4-byte floating points that
235 were written on a machine of different byte-order than yours. You can
236 swap the byte-order with
237 xyz2grd floats.bin -Snew_floats.bin -V -Zf
239
241 GMT(1), grd2xyz(1), grdedit(1)
242GMT 4.5.6 10 Mar 2011 XYZ2GRD(1)