blockmode
blockmode - Block average (x,y,z) data tables by mode estimation
Synopsis
blockmode [ table ]
-Iincrement
-Rregion
[ -C ]
[ -D[width][+c][+a|+l|+h ]
[ -Er|s[-] ] [ -Q ]
[ -V[level] ]
[ -W[i|o] ]
[ -b<binary> ]
[ -d<nodata> ]
[ -f<flags> ]
[ -h<headers> ]
[ -i<flags> ]
[ -o<flags> ]
[ -r ]
[ -:[i|o] ]
Note: No space is allowed between the option flag and the associated arguments.
Description
blockmode 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 mode estimates of
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, blockmode will read from standard input.
- -C
- Use the center of the block as the output location [Default uses the
modal xy location (but see -Q)]. -C overrides -Q.
- -D[width][+c][+a|+l|+h ]
- Perform unweighted mode calculation via histogram binning, using the
specified histogram width. Append +c to center bins so that
their mid point is a multiple of width [uncentered].
If multiple modes are found for a block we return the average mode [+a].
Append +l or +h to return the low of high mode instead, respectively.
If width is not given it will default to 1 provided your data set only
contains integers. Also, for integer data and integer bin width we
enforce bin centering (+c) and select the lowest mode (+l) if
there are multiples. [Default mode is normally the Least Median of Squares (LMS) statistic].
- -E
- Provide Extended report which includes s (the L1 scale of the
mode), 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.
- -Er|s[-]
- Provide source id s or record number r output, i.e., append
the source id or record number associated with the modal value. If
tied then report the record number of the higher of the two values;
append - to instead report the record number of the lower value.
Note that both -E and -Er[-] may be specified.
For -Es we expect input records of the form
x,y,z[,w],sid, where sid is an unsigned integer
source id.
- -Q
- (Quicker) Finds mode z and mean (x,y) [Default finds mode
x, mode y, mode z].
- -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.
- -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 mode estimates from the double precision
binary data in hawaii_b.xyg and output an ASCII table, run:
gmt blockmode hawaii_b.xyg -R198/208/18/25 -I5m -bi3d > hawaii_5x5.xyg
To determine the most frequently occurring values per 5x5 block using histogram binning, with
data representing integer counts, try
gmt blockmode data.txt -R0/100/0/100 -I5 -r -C -D