blockmean - Block average (x, y, z) data tables by L2 norm
blockmean [ table ]
-Rregion [ -C ] [ -E[p] ] [
-S[m|n|s|w] ] [ -V[level] ] [
-W[i|o][+s] ] [ -bbinary ] [
-dnodata ] [ -eregexp ] [ -fflags ] [ -hheaders ]
[ -iflags ] [ -oflags ] [ -r ] [
Note: No space is allowed between the option flag and the
blockmean reads arbitrarily located (x,y,z) triples
[or optionally weighted quadruples (x,y,z,w)] from
standard input [or table] and writes to standard output a mean position
and value for every non-empty block in a grid region defined by the -R
and -I arguments. Either blockmean, blockmedian, or blockmode
should be used as a pre-processor before running surface to avoid aliasing
short wavelengths. These routines are also generally useful for decimating or
averaging (x,y,z) data. You can modify the precision of
the output format by editing the FORMAT_FLOAT_OUT parameter in your gmt.conf
file, or you may choose binary input and/or output to avoid loss of precision.
- x_inc [and optionally y_inc] is the grid spacing.
Optionally, append a suffix modifier. Geographical (degrees)
coordinates: Append m to indicate arc minutes or s to
indicate arc seconds. If one of the units e, f, k,
M, n or u is appended instead, the increment is
assumed to be given in meter, foot, km, Mile, nautical mile or US survey
foot, respectively, and will be converted to the equivalent degrees
longitude at the middle latitude of the region (the conversion depends on
PROJ_ELLIPSOID). If y_inc is given but set to 0 it will be reset
equal to x_inc; otherwise it will be converted to degrees latitude.
All coordinates: If +e is appended then the corresponding
max x (east) or y (north) 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 number of nodes desired by
appending +n 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 App-file-formats for details. Note: if
-Rgrdfile is used then the grid spacing has already been
initialized; use -I to override the values.
- Specify the region of interest.
- 3 [or 4, see -W] column ASCII data table file(s) [or binary, see
-bi] holding (x,y,z[,w]) data values.
[w] is an optional weight for the data. If no file is specified,
blockmean will read from standard input.
- Use the center of the block as the output location [Default uses the mean
- Provide Extended report which includes s (the standard deviation
about the mean), l, the lowest value, and h, the high value
for each block. Output order becomes
outputs x,y,z[,w]. See -W for w
output. If -Ep is used we assume weights are 1/(sigma squared) and
s becomes the propagated error of the mean.
- Use -Sn to report the number of points inside each block,
-Ss to report the sum of all z-values inside a block,
-Sw to report the sum of weights [Default (or -Sm reports
- -V[level] (more ...)
- Select verbosity level [c].
- Weighted modifier[s]. Unweighted input and output have 3 columns
x,y,z; Weighted i/o has 4 columns
x,y,z,w. Weights can be used in input to
construct weighted mean values for each block. Weight sums can be reported
in output for later combining several runs, etc. Use -W for
weighted i/o, -Wi for weighted input only, and -Wo for
weighted output only. [Default uses unweighted i/o]. If your weights are
actually uncertainties (one sigma) then append +s and we compute
weight = 1/sigma.
- -bi[ncols][t] (more ...)
- Select native binary input. [Default is 3 (or 4 if -Wi is
- -bo[ncols][type] (more ...)
- Select native binary output. [Default is 3 (or 4 if -Wo is set)].
-E adds 3 additional columns. The -Sn option will work with
only 2 input columns (x and y).
- -d[i|o]nodata (more ...)
- Replace input columns that equal nodata with NaN and do the reverse
- -e[~]"pattern" |
-e[~]/regexp/[i] (more ...)
- Only accept data records that match the given pattern.
- -f[i|o]colinfo (more ...)
- Specify data types of input and/or output columns.
- Skip or produce header record(s).
- Select input columns and transformations (0 is first column).
- -ocols[,...] (more ...)
- Select output columns (0 is first column).
- -r (more ...)
- Set pixel node registration [gridline]. Each block is the locus of points
nearest the grid value location. Consider an example with
-R10/15/10/15 and -I1: With the -r option, 10 <=
(x,y) < 11 is one of 25 blocks; without it 9.5 <=
(x,y) < 10.5 is one of 36 blocks.
- -:[i|o] (more ...)
- Swap 1st and 2nd column on input and/or output.
- -^ or just -
- Print a short message about the syntax of the command, then exits (NOTE:
on Windows just use -).
- -+ or just +
- Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.
- -? or no arguments
- Print a complete usage (help) message, including the explanation of all
options, then exits.
ASCII FORMAT PRECISION¶
The ASCII output formats of numerical data are controlled by parameters in your
gmt.conf file. Longitude and latitude are formatted according to
FORMAT_GEO_OUT, absolute time is under the control of FORMAT_DATE_OUT and
FORMAT_CLOCK_OUT, whereas general floating point values are formatted
according to FORMAT_FLOAT_OUT. Be aware that the format in effect can lead to
loss of precision in ASCII output, which can lead to various problems
downstream. If you find the output is not written with enough precision,
consider switching to binary output (-bo if available) or specify more
decimals using the FORMAT_FLOAT_OUT setting.
To find 5 by 5 minute block mean values from the ASCII data in hawaii.xyg, run
gmt blockmean hawaii.xyg -R198/208/18/25 -I5m > hawaii_5x5.xyg
blockmedian, blockmode, gmt, gmt.conf, greenspline, nearneighbor,
sphtriangulate, surface, triangulate
2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe