1BLOCKMODE(1) Generic Mapping Tools BLOCKMODE(1)
2
6 blockmode - filter to block average (x,y,z) data by mode estimation.
7
9 blockmode [ xyz[w]file(s) ] -Ixinc[unit][=|+][/yinc[unit][=|+]]
10 -Rxmin/xmax/ymin/ymax[r] [ -C ] [ -E ] [ -F ] [ -H[i][nrec] ] [ -Q ] [
11 -V ] [ -W[io] ] [ -:[i|o] ] [ -b[i|o][s|S|d|D[ncol]|c[var1/...]] ] [
12 -f[i|o]colinfo ]
13
15 blockmode reads arbitrarily located (x,y,z) triples [or optionally
16 weighted quadruples (x,y,z,w)] from standard input [or xyz[w]file(s)]
17 and writes to standard output mode estimates of position and value for
18 every non-empty block in a grid region defined by the -R and -I argu‐
19 ments. Either blockmean, blockmedian, or blockmode should be used as a
20 pre-processor before running surface to avoid aliasing short wave‐
21 lengths. These routines are also generally useful for decimating or
22 averaging (x,y,z) data. You can modify the precision of the output
23 format by editing the D_FORMAT parameter in your .gmtdefaults4 file, or
24 you may choose binary input and/or output using single or double preci‐
25 sion storage.
26 xyz[w]file(s)
28 3 [or 4] column ASCII file(s) [or binary, see -b] holding
29 (x,y,z[,w]) data values. [w] is an optional weight for the
30 data. If no file is specified, blockmode will read from stan‐
31 dard input.
32 -I x_inc [and optionally y_inc] is the grid spacing. Optionally,
34 append a suffix modifier. Geographical (degrees) coordinates:
35 Append m to indicate arc minutes or c to indicate arc seconds.
36 If one of the units e, k, i, or n is appended instead, the
37 increment is assumed to be given in meter, km, miles, or nauti‐
38 cal miles, respectively, and will be converted to the equivalent
39 degrees longitude at the middle latitude of the region (the con‐
40 version depends on ELLIPSOID). If /y_inc is given but set to 0
41 it will be reset equal to x_inc; otherwise it will be converted
42 to degrees latitude. All coordinates: If = is appended then the
43 corresponding max x (east) or y (north) may be slightly adjusted
44 to fit exactly the given increment [by default the increment may
45 be adjusted slightly to fit the given domain]. Finally, instead
46 of giving an increment you may specify the number of nodes
47 desired by appending + to the supplied integer argument; the
48 increment is then recalculated from the number of nodes and the
49 domain. The resulting increment value depends on whether you
50 have selected a gridline-registered or pixel-registered grid;
51 see Appendix B for details.
52 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
54 geographic regions, these limits correspond to west, east,
55 south, and north and you may specify them in decimal degrees or
56 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
57 and upper right map coordinates are given instead of w/e/s/n.
58 The two shorthands -Rg and -Rd stand for global domain (0/360
59 and -180/+180 in longitude respectively, with -90/+90 in lati‐
60 tude). For calendar time coordinates you may either give (a)
61 relative time (relative to the selected TIME_EPOCH and in the
62 selected TIME_UNIT; append t to -JX|x), or (b) absolute time of
63 the form [date]T[clock] (append T to -JX|x). At least one of
64 date and clock must be present; the T is always required. The
65 date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
66 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
67 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
68 iters and their type and positions must be exactly as indicated
69 (however, input, output and plot formats are customizable; see
70 gmtdefaults).
71
73 -C Use the center of the block as the output location [Default uses
74 the modal xy location (but see -Q)]. -C overrides -Q.
75 -E Provide Extended report which includes s (the L1 scale of the
77 mode), l, the lowest value, and h, the high value for each
78 block. Output order becomes x,y,z,s,l,h[,w]. [Default outputs
79 x,y,z[,w]. See -W for w output.
80 -F Force pixel node registration [Default is gridline registra‐
82 tion]. (Node registrations are defined in GMT Cookbook Appendix
83 B on grid file formats.) Each block is the locus of points
84 nearest the grid value location. For example, with
85 -R10/15/10/15 and and -I1: with the -F option 10 <= (x,y) < 11
86 is one of 25 blocks; without it 9.5 <= (x,y) < 10.5 is one of 36
87 blocks.
88 -H Input file(s) has Header record(s). Number of header records
90 can be changed by editing your .gmtdefaults4 file. If used, GMT
91 default is 1 header record. Use -Hi if only input data should
92 have header records [Default will write out header records if
93 the input data have them]. Blank lines and lines starting with #
94 are always skipped. Not used with binary data.
95 -Q (Quicker) Finds mode z and mean (x, y) [Default finds mode x,
97 mode y, mode z].
98 -V Selects verbose mode, which will send progress reports to stderr
100 [Default runs "silently"].
101 -W Weighted modifier[s]. Unweighted input and output has 3 columns
103 x,y,z; Weighted i/o has 4 columns x,y,z,w. Weights can be used
104 in input to construct weighted mean values in blocks. Weight
105 sums can be reported in output for later combining several runs,
106 etc. Use -W for weighted i/o, -Wi for weighted inputonly, -Wo
107 for weighted output only. [Default uses unweighted i/o].
108 -: Toggles between (longitude,latitude) and (latitude,longitude)
110 input and/or output. [Default is (longitude,latitude)]. Append
111 i to select input only or o to select output only. [Default
112 affects both].
113 -bi Selects binary input. Append s for single precision [Default is
115 d (double)]. Uppercase S or D will force byte-swapping.
116 Optionally, append ncol, the number of columns in your binary
117 input file if it exceeds the columns needed by the program. Or
118 append c if the input file is netCDF. Optionally, append
119 var1/var2/... to specify the variables to be read. [Default is
120 3 (or 4 if -Wi is set)].
121 -bo Selects binary output. Append s for single precision [Default
123 is d (double)]. Uppercase S or D will force byte-swapping.
124 Optionally, append ncol, the number of desired columns in your
125 binary output file. [Default is 3 (or 4 if -Wo is set)]. -E
126 adds 3 additional columns.
127 -f Special formatting of input and/or output columns (time or geo‐
129 graphical data). Specify i or o to make this apply only to
130 input or output [Default applies to both]. Give one or more
131 columns (or column ranges) separated by commas. Append T (abso‐
132 lute calendar time), t (relative time in chosen TIME_UNIT since
133 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
134 to each column or column range item. Shorthand -f[i|o]g means
135 -f[i|o]0x,1y (geographic coordinates).
136
138 The ASCII output formats of numerical data are controlled by parameters
139 in your .gmtdefaults4 file. Longitude and latitude are formatted
140 according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
141 according to D_FORMAT. Be aware that the format in effect can lead to
142 loss of precision in the output, which can lead to various problems
143 downstream. If you find the output is not written with enough preci‐
144 sion, consider switching to binary output (-bo if available) or specify
145 more decimals using the D_FORMAT setting.
146
148 To find 5 by 5 minute block mode estimates from the double precision
149 binary data in hawaii_b.xyg and output an ASCII table, run:
150 blockmode hawaii_b.xyg -R198/208/18/25 -I5m -bi3 > hawaii_5x5.xyg
152
154 blockmean(1), blockmedian(1), GMT(1), gmtdefaults(1), nearneighbor(1),
155 surface(1), triangulate(1)
156GMT 4.3.1 15 May 2008 BLOCKMODE(1)