NAME
blockmode - filter to block average (x,y,z) data by mode estimation.
SYNOPSIS
blockmode [ xyz[w]file(s) ] -Ix_inc[m|c][/y_inc[m|c]]
-Rwest/east/south/north[r] [ -C ] [ -F ] [ -H[nrec] ] [ -L ] [ -Q ] [
-V ] [ -W[io] ] [ -: ] [ -bi[s][n] ] [ -bo[s][n] ]
DESCRIPTION
blockmode reads arbitrarily located (x,y,z) triples [or optionally
weighted quadruples (x,y,z,w)] from standard input [or xyz[w]file(s)]
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 argu-
ments. Either blockmean, blockmedian, or blockmode should be used as a
pre-processor before running surface to avoid aliasing short wave-
lengths. These routines are also generally useful for decimating or
averaging (x,y,z) data. You can modify the precision of the output for-
mat by editing the D_FORMAT parameter in your .gmtdefaults file, or you
may choose binary input and/or output using single or double precision
storage.
xyz[w]file(s)
3 [or 4] column ASCII file(s) [or binary, see -b] 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.
-I x_inc [and optionally y_inc] is the grid spacing. Append m to
indicate minutes or c to indicate seconds.
-R west, east, south, and north specify the Region of interest. To
specify boundaries in degrees and minutes [and seconds], use the
dd:mm[:ss] format. Append r if lower left and upper right map
coordinates are given instead of wesn.
OPTIONS
-C Use the center of the block as the output location [Default uses
the modal xy location (but see -Q)]. -C overrides -Q.
-F Block centers have pixel registration. [Default: grid registra-
tion.] (Registrations are defined in GMT Cookbook Appendix B on
grid file formats.) Each block is the locus of points nearest
the grid value location. For example, with -R10/15/10/15 and and
-I1: with the -F option 10 <= (x,y) < 11 is one of 25 blocks;
without it 9.5 <= (x,y) < 10.5 is one of 36 blocks.
-H Input file(s) has Header record(s). Number of header records can
be changed by editing your .gmtdefaults file. If used, GMT
default is 1 header record. Not used with binary data.
-L Indicates that the x column contains longitudes, which may dif-
fer from the region in -R by [multiples of] 360 degrees [Default
assumes no periodicity].
-Q (Quicker) Finds mode z and mean (x, y) [Default finds mode x,
mode y, mode z].
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-W 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 modal 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]
-: Toggles between (longitude,latitude) and (latitude,longitude)
input/output. [Default is (longitude,latitude)]. Applies to
geographic coordinates only.
-bi Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
file(s). [Default is 3 (or 4 if -W is set) columns].
-O Selects Overlay plot mode [Default initializes a new plot sys-
tem].
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, try
blockmode hawaii_b.xyg -R198/208/18/25 -I5m -bi3 > hawaii_5x5.xyg
SEE ALSO
blockmean(l), blockmedian(l), gmt(l), gmtdefaults(l), nearneighbor(l),
surface(l), triangulate(l)
GMT3.4.6 1 Jan 2005 BLOCKMODE(l)
Man(1) output converted with
man2html