1GRD2XYZ(1) Generic Mapping Tools GRD2XYZ(1)
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6 grd2xyz - Converting grid file(s) to ASCII or binary data
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9 grd2xyz grdfiles [ -E[nodata] ] [ -H[i][nrec] ] [
10 -Rwest/east/south/north[r] ] [ -S[r] ] [ -V ] [ -W[weight] ] [
11 -Z[flags] ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ] [ -fcolinfo ]
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14 grd2xyz reads one or more binary 2-D grid files and writes out xyz-
15 triplets in ASCII [or binary] format to standard output. Modify the
16 precision of the ASCII output format by editing the D_FORMAT parameter
17 in your .gmtdefaults4 file or use --D_FORMAT=format on the command
18 line, or choose binary output using single or double precision storage.
19 As an option you may output z-values without the (x,y) in a number of
20 formats, see -E or -Z below.
21 grdfiles
23 Names of 2-D binary grid files to be converted. (See GRID FILE
24 FORMATS below.)
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27 -E Output an ESRI ArcInfo ASCII interchange grid format file.
28 Append nodata which will be used wherever the grid value equals
29 NaN [-9999]. Note that all data values are written as integers.
30 -H Output 1 header record based on information in the first grid
32 file header. Ignored if binary output is selected. [Default is
33 no header].
34 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
36 geographic regions, these limits correspond to west, east,
37 south, and north and you may specify them in decimal degrees or
38 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
39 and upper right map coordinates are given instead of w/e/s/n.
40 The two shorthands -Rg and -Rd stand for global domain (0/360
41 and -180/+180 in longitude respectively, with -90/+90 in lati‐
42 tude). For calendar time coordinates you may either give (a)
43 relative time (relative to the selected TIME_EPOCH and in the
44 selected TIME_UNIT; append t to -JX|x), or (b) absolute time of
45 the form [date]T[clock] (append T to -JX|x). At least one of
46 date and clock must be present; the T is always required. The
47 date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
48 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
49 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
50 iters and their type and positions must be exactly as indicated
51 (however, input, output and plot formats are customizable; see
52 gmtdefaults). Using the -R option will select a subsection of
53 the grid. If this subsection exceeds the boundaries of the grid,
54 only the common region will be output.
55 -S Suppress output for nodes whose z-value equals NaN [Default out‐
57 puts all nodes]. Append r to reverse the suppression, i.e.,
58 only output the nodes whose z-value equals NaN.
59 -V Selects verbose mode, which will send progress reports to stderr
61 [Default runs "silently"].
62 -W Write out x,y,z,w, where w is the supplied weight (or 1 if not
64 supplied) [Default writes x,y,z only].
65 -Z Write a 1-column ASCII [or binary] table. Output will be orga‐
67 nized according to the specified ordering convention contained
68 in flags. If data should be written by rows, make flags start
69 with T(op) if first row is y = ymax or B(ottom) if first row is
70 y = ymin. Then, append L or R to indicate that first element
71 should start at left or right end of row. Likewise for column
72 formats: start with L or R to position first column, and then
73 append T or B to position first element in a row. For gridline
74 registered grids: If grid is periodic in x but the outcoming
75 data should not contain the (redundant) column at x = xmax,
76 append x. For grid periodic in y, skip writing the redundant
77 row at y = ymax by appending y. If the byte-order needs to be
78 swapped, append w. Select one of several data types (all binary
79 except a):
80 a ASCII representation
82 c signed 1-byte character
83 u unsigned 1-byte character
84 h short 2-byte integer
85 i 4-byte integer
86 l long (4- or 8-byte) integer [architecture-dependent!]
87 f 4-byte floating point single precision
88 d 8-byte floating point double precision
89 Default format is scanline orientation of ASCII numbers: -ZTLa.
91 Note that -Z only applies to 1-column output.
92 -bo Selects binary output. Append s for single precision [Default
94 is d (double)]. Uppercase S or D will force byte-swapping.
95 Optionally, append ncol, the number of desired columns in your
96 binary output file. [Default is 3]. This option only applies
97 to xyz output; see -Z for z table output.
98 -f Special formatting of input and/or output columns (time or geo‐
100 graphical data). Specify i or o to make this apply only to
101 input or output [Default applies to both]. Give one or more
102 columns (or column ranges) separated by commas. Append T (abso‐
103 lute calendar time), t (relative time in chosen TIME_UNIT since
104 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
105 to each column or column range item. Shorthand -f[i|o]g means
106 -f[i|o]0x,1y (geographic coordinates). See also TIME COORDI‐
107 NATES below.
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110 The ASCII output formats of numerical data are controlled by parameters
111 in your .gmtdefaults4 file. Longitude and latitude are formatted
112 according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
113 according to D_FORMAT. Be aware that the format in effect can lead to
114 loss of precision in the output, which can lead to various problems
115 downstream. If you find the output is not written with enough preci‐
116 sion, consider switching to binary output (-bo if available) or specify
117 more decimals using the D_FORMAT setting.
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120 GMT is able to recognize many of the commonly used grid file formats,
121 as well as the precision, scale and offset of the values contained in
122 the grid file. When GMT needs a little help with that, you can add the
123 suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of
124 the grid type and precision, and scale and offset are optional scale
125 factor and offset to be applied to all grid values, and nan is the
126 value used to indicate missing data. See grdreformat(1) and Section
127 4.17 of the GMT Technical Reference and Cookbook for more information.
128 When reading a netCDF file that contains multiple grids, GMT will read,
130 by default, the first 2-dimensional grid that can find in that file. To
131 coax GMT into reading another multi-dimensional variable in the grid
132 file, append ?varname to the file name, where varname is the name of
133 the variable. Note that you may need to escape the special meaning of ?
134 in your shell program by putting a backslash in front of it, or by
135 placing the filename and suffix between quotes or double quotes. See
136 grdreformat(1) and Section 4.18 of the GMT Technical Reference and
137 Cookbook for more information, particularly on how to read splices of
138 3-, 4-, or 5-dimensional grids.
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141 Time coordinates in netCDF grids, be it the x, y, or z coordinate, will
142 be recognized as such. The variable's unit attribute is parsed to
143 determine the unit and epoch of the time coordinate in the grid. Val‐
144 ues are then converted to the internal time system specified by
145 TIME_UNIT and TIME_EPOCH in the .gmtdefaults file or on the command
146 line. The default output is relative time in that time system, or
147 absolute time when using the option -f0T, -f1T, or -f2T for x, y, or z
148 coordinate, respectively.
149
151 To edit individual values in the 5' by 5' hawaii_grv.grd file, dump the
152 .grd to ASCII:
153 grd2xyz hawaii_grv.grd > hawaii_grv.xyz
155 To write a single precision binary file without the x,y positions from
157 the file raw_data.grd file, using scanline orientation, run
158 grd2xyz raw_data.grd -ZTLf > hawaii_grv.b
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162 gmtdefaults(1), GMT(1), grdedit(1), xyz2grd(1)
163GMT 4.3.1 15 May 2008 GRD2XYZ(1)