xenial (1) blockmean.1gmt.gz

Provided by: gmt-common_5.2.1+dfsg-3build1_all bug

NAME

       blockmean - Block average (x, y, z) data tables by L2 norm

SYNOPSIS

       blockmean  [  table  ] increment region [  ] [ [p] ] [ [m|n|s|w] ] [ [level] ] [ [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

       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 App-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.

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, whereas other values are formatted according to
       FORMAT_FLOAT_OUT. Be aware that the format in effect can lead to loss of precision in the  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.

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

SEE ALSO

       blockmedian, blockmode, gmt, gmt.conf, greenspline, nearneighbor, sphtriangulate, surface, triangulate

       2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe