blockmean
blockmean - Block average (x,y,z) data tables by L2 norm
Description
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.
Required Arguments
- -Ixinc[unit][=|+][/yinc[unit][=|+]]
- 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 = 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 + 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 GMT File Formats for
details. Note: if -Rgrdfile is used then the grid spacing has
already been initialized; use -I to override the values.
- -R[unit]xmin/xmax/ymin/ymax[r] (more ...)
- Specify the region of interest.
Optional Arguments
- table
- 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.
- -C
- Use the center of the block as the output location [Default uses the mean location].
- -E[p]
- 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
x,y,z,s,l,h[,w]. [Default 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.
- -S[m|n|s|w]
- 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 mean value].
- -V[level] (more ...)
- Select verbosity level [c].
- -W[i|o]
- Weighted modifier[s]. Unweighted input and output has 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 in
blocks. Weight sums can be reported in output for later combining
several runs, etc. Use -W for weighted i/o, -Wi for weighted
input only, -Wo for weighted output only. [Default uses
unweighted i/o].
- -bi[ncols][t] (more ...)
- Select native binary input. [Default is 3 (or 4 if -Wi is set)].
- -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 on output.
- -f[i|o]colinfo (more ...)
- Specify data types of input and/or output columns.
- -h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
- Skip or produce header record(s).
- -icols[l][sscale][ooffset][,...] (more ...)
- Select input columns (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. For 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 use just -).
- -+ 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
options, then exits.
- --version
- Print GMT version and exit.
- --show-datadir
- Print full path to GMT share directory and exit.
Examples
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