blockmode(cmd0::String="", arg1=nothing; kwargs...)


Block average (x,y,z) data tables by mode estimation.

Reads arbitrarily located (x,y,z) triples [or optionally weighted quadruples (x,y,z,w)] and computes a mode position and value for every non-empty block in a grid region defined by the region and increment parameters.

Takes a Mx3 matrix, a GMTdataset, or a file name as input and returns either a table (a GMTdataset) or one or more grids (GMTgrid). Aternatively, save the result directly in a disk file.

Required Arguments

3 (or 4, see weights) column data table file (or binary, see binary_in) holding (x,y,z[,w]) data values, where [ w] is an optional weight for the data.

  • I or inc or increment or spacing : – inc=x_inc | inc=(xinc, yinc) | inc="xinc[+e|n][/yinc[+e|n]]"
    Specify the grid increments or the block sizes. More at spacing

  • R or region or limits : – limits=(xmin, xmax, ymin, ymax) | limits=(BB=(xmin, xmax, ymin, ymax),) | limits=(LLUR=(xmin, xmax, ymin, ymax),units="unit") | ...more
    Specify the region of interest. More at limits. For perspective view view, optionally add zmin,zmax. This option may be used to indicate the range used for the 3-D axes. You may ask for a larger w/e/s/n region to have more room between the image and the axes.

Optional Arguments

  • A or field or fields: – field=mode|scale|highest|lowest|weights
    Output is a grid with one of the select fields. field=mode writes the modal data z. Other options are: scale (the L1 scale of the mode), lowest (lowest value), highest (highest value) and weights (the output weight; requires the weights option). The deafault is field=mode. Alternatively, one can use a condensed form which uses the first character (except the mean) of the above options, separated by commas, to compute more than one grid. For example: fields="z,h" computes two grids; one with the modes and the other with the highest values in blocks.

  • C or center : – center=true
    Use the center of the block as the output location [Default uses the modal xy location (but see quick)]. center overrides quick.

  • D or histogram_binning : – histogram_binning=true | histogram_binning=[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 or extend : –- extend=true | extend="r|s[+l|+h]"
    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 weights for enabling w output.

    If extend="r|s[+l|+h]" is used then provide source id s or record number r output, i.e., append the source id or record number associated with the median value. If tied then report the record number of the higher of the two values (i.e., +h is the default); append +l to instead report the record number of the lower value.

    Note that extend may be repeated so that both extend=true and extend="r[+l|+h]" can be specified. But in this case (repeated extend option) one must encapsulate the intire option in a Tuple because option names can not be repeated (not yet imlemented). For extend=:s we expect input records of the form x,y,z[,w],sid, where sid is an unsigned integer source id.

  • G or save or outgrid or outfile : – save=file_name.grd
    Write one or more fields directly to grids on disk; no data is returned to the Julia REPL. If more than one fields are specified via fields then file_name must contain the format flag %s so that we can embed the field code in the file names.

  • Q or quick : – quick=true
    (Quicker) Finds median z and (x,y) at that the median z [Default finds median x, median y independent of z]. Also see center.

  • T or quantile : – quantile=val
    Sets the quantile of the distribution to be returned [Default is 0.5 which returns the median z]. Here, 0 < val < 1.

  • V or verbose : – verbose=true | verbose=level
    Select verbosity level. More at verbose

  • W or weights : – weights=:i | weights=:o | weights="i+s" | weights="i|o+s|+w"
    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 weights for weighted i/o, weights=:i for weighted input only, and weights=:o for weighted output only. [Default uses unweighted i/o]. If your weights are actually uncertainties (one sigma) then append the string +s (as in weights="i+s") and we compute weight = 1/sigma. Otherwise (or via +w) we use the weights directly.

  • bi or binary_in : – binary_in=??
    Select native binary format for primary table input. More at

  • bo or binary_out : – binary_out=??
    Select native binary format for table output. More at

  • di or nodata_in : – nodata_in=??
    Substitute specific values with NaN. More at

  • e or pattern : – pattern=??
    Only accept ASCII data records that contain the specified pattern. More at

  • f or colinfo : – colinfo=??
    Specify the data types of input and/or output columns (time or geographical data). More at

  • h or header : – header=??
    Specify that input and/or output file(s) have n header records. More at

  • i or incol or incols : – incol=col_num | incol="opts"
    Select input columns and transformations (0 is first column, t is trailing text, append word to read one word only). More at incol

  • o or outcol : – outcol=??
    Select specific data columns for primary output, in arbitrary order. More at

  • q or inrows : – inrows=??
    Select specific data rows to be read and/or written. More at

  • r or reg or registration : – reg=:p | reg=:g
    Select gridline or pixel node registration. Used only when output is a grid. More at

  • w or wrap or cyclic : – wrap=??
    Convert input records to a cyclical coordinate. More at

  • yx : – yx=true
    Swap 1st and 2nd column on input and/or output. More at


To find 5 by 5 minute block mode values from the ASCII data in ship_15.txt, run

D = blockmode("@ship_15.txt", region=(245,255,20,30), inc="5m");

To determine the most frequently occurring values per 2x2 block using histogram binning, with data representing integer counts, try:

D = blockmode("@ship_15.txt", region=:global, inc="5m", center=true, histogram_binning=true);

To determine the mode and L1 scale (MAD) on the mode per 10 minute bin and save these to two separate grids called and, run:

blockmode("@ship_15.txt", spacing="10m", region=(-115,-105,20,30), extend=true, save="", fields="z,s")

See Also

The GMT man page blockmean blockmedian