.. index:: ! blockmedian *********** blockmedian *********** .. only:: not man blockmedian - Block average (*x*,\ *y*,\ *z*) data tables by L1 norm Synopsis -------- .. include:: common_SYN_OPTs.rst_ **blockmedian** [ *table* ] |SYN_OPT-I| |SYN_OPT-R| [ |-C| ] [ |-E|\ [**b**] ] [ |-E|\ **r**\ \|\ **s**\ [**-**] ] [ |-Q| ] [ |-T|\ *quantile* ] [ |SYN_OPT-V| ] [ |-W|\ [**i**\ \|\ **o**][**+s**] ] [ |SYN_OPT-b| ] [ |SYN_OPT-d| ] [ |SYN_OPT-e| ] [ |SYN_OPT-f| ] [ |SYN_OPT-h| ] [ |SYN_OPT-i| ] [ |SYN_OPT-o| ] [ **-r** ] [ |SYN_OPT-:| ] |No-spaces| Description ----------- **blockmedian** 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 median position and value for every non-empty block in a grid region defined by the **-R** and **-I** arguments. Either :doc:`blockmean`, **blockmedian**, or :doc:`blockmode` should be used as a pre-processor before running :doc:`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 :ref:`FORMAT_FLOAT_OUT ` parameter in your :doc:`gmt.conf` file, or you may choose binary input and/or output to avoid loss of precision. Required Arguments ------------------ .. _-I: .. include:: explain_-I.rst_ .. |Add_-R| unicode:: 0x20 .. just an invisible code .. include:: explain_-R.rst_ Optional Arguments ------------------ *table* 3 [or 4, see **-W**] column ASCII data table] column ASCII 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, **blockmedian** will read from standard input. .. _-C: **-C** Use the center of the block as the output location [Default uses the median x and median y as location (but see **-Q**)]. .. _-E: **-E**\ [**b**\ ] Provide Extended report which includes **s** (the L1 scale of the median), **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*]. For box-and-whisker calculation, use **-Eb** which will output *x*,\ *y*,\ *z*,\ *l*,\ *q25*,\ *q75*,\ *h*\ [,\ *w*], where *q25* and *q75* are the 25% and 75% quantiles, respectively. See **-W** for *w* output. **-E**\ **r**\ \|\ **s**\ [**-**\ ] 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; append **-** to instead report the record number of the lower value. Note that both **-E**\ [**b**\ ] and **-E**\ **r**\ [**-**\ ] may be specified. For **-E**\ **s** we expect input records of the form *x*,\ *y*,\ *z*\ [,\ *w*],\ *sid*, where *sid* is an unsigned integer source id. .. _-Q: **-Q** (Quicker) Finds median *z* and (*x*,\ *y*) at that the median *z* [Default finds median *x*, median *y* independent of *z*]. Also see **-C**. .. _-T: **-T**\ *quantile* Sets the *quantile* of the distribution to be returned [Default is 0.5 which returns the median *z*]. Here, 0 < *quantile* < 1. .. _-V: .. |Add_-V| unicode:: 0x20 .. just an invisible code .. include:: explain_-V.rst_ .. _-W: **-W**\ [**i**\ \|\ **o**][**+s**] 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 median values for each block. Weight sums can be reported in output for later combining several runs, etc. Use **-W** for weighted i/o, **-Wi** for weighted input only, and **-Wo** for weighted output only. [Default uses unweighted i/o]. If your weights are actually uncertainties (one sigma) then append **+s** and we compute weight = 1/sigma. .. |Add_-bi| replace:: [Default is 3 (or 4 if **-Wi** is set)]. .. include:: explain_-bi.rst_ .. |Add_-bo| replace:: [Default is 3 (or 4 if **-Wo** is set)]. **-E** adds 3 additional columns. .. include:: explain_-bo.rst_ .. |Add_-d| unicode:: 0x20 .. just an invisible code .. include:: explain_-d.rst_ .. |Add_-e| unicode:: 0x20 .. just an invisible code .. include:: explain_-e.rst_ .. |Add_-f| unicode:: 0x20 .. just an invisible code .. include:: explain_-f.rst_ .. |Add_-h| unicode:: 0x20 .. just an invisible code .. include:: explain_-h.rst_ .. include:: explain_-icols.rst_ .. include:: explain_-ocols.rst_ .. |Add_nodereg| replace:: Each block is the locus of points nearest the grid value location. Consider an example with **-R**\ 10/15/10/15 and **-I**\ 1: 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. .. include:: explain_nodereg.rst_ .. include:: explain_colon.rst_ .. include:: explain_help.rst_ .. include:: explain_precision.rst_ Examples -------- To find 5 by 5 minute block medians from the double precision binary data in hawaii_b.xyg and output an ASCII table, run :: gmt blockmedian hawaii_b.xyg -R198/208/18/25 -I5m -bi3d > hawaii_5x5.xyg To compute the shape of a data distribution per bin via a box-and-whisker diagram we need the 0%, 25%, 50%, 75%, and 100% quantiles. To do so on a global 5 by 5 degree basis from the ASCII table depths.xyz and send output to an ASCII table, run :: gmt blockmedian depths.xyz -Rg -I5 -Eb -r > depths_5x5.txt See Also -------- :doc:`blockmean`, :doc:`blockmode`, :doc:`gmt`, :doc:`gmt.conf`, :doc:`greenspline`, :doc:`nearneighbor`, :doc:`surface`, :doc:`sphtriangulate`, :doc:`triangulate`