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.. index:: ! filter1d
********
filter1d
********
.. only:: not man
filter1d - Time domain filtering of 1-D data tables
Synopsis
--------
.. include:: common_SYN_OPTs.rst_
**filter1d** [ *table* ] |-F|\ *type<width>*\ [*mode*][**+h**]
[ |-D|\ *increment* ] [ |-E| ] [ |-I|\ *ignore\_val* ]
[ |-L|\ *lack\_width* ] [ |-N|\ *t\_col* ] [ |-Q|\ *q\_factor* ]
[ |-S|\ *symmetry\_factor* ] [ |-T|\ *t\_min/t\_max/t\_inc*\ [**+**] ]
[ |SYN_OPT-V| ]
[ |SYN_OPT-b| ]
[ |SYN_OPT-d| ]
[ |SYN_OPT-f| ]
[ |SYN_OPT-g| ]
[ |SYN_OPT-h| ]
[ |SYN_OPT-i| ]
[ |SYN_OPT-o| ]
[ |SYN_OPT-:| ]
|No-spaces|
Description
-----------
**filter1d** is a general time domain filter for multiple column time
series data. The user specifies which column is the time (i.e., the
independent variable). (See **-N** option below). The fastest operation
occurs when the input time series are equally spaced and have no gaps or
outliers and the special options are not needed. **filter1d** has
options **-L**, **-Q**, and **-S** for unevenly sampled data with gaps.
Required Arguments
------------------
.. _-F:
**-F**\ *type<width>*\ [*mode*][**+h**]
Sets the filter *type*. Choose among convolution and non-convolution
filters. Append the filter code followed by the full filter
*<width>* in same units as time column. Available convolution
filters are:
(**b**) Boxcar: All weights are equal.
(**c**) Cosine Arch: Weights follow a cosine arch curve.
(**g**) Gaussian: Weights are given by the Gaussian function.
(**f**) Custom: Instead of *width* give name of a one-column file
with your own weight coefficients.
Non-convolution filters are:
(**m**) Median: Returns median value.
(**p**) Maximum likelihood probability (a mode estimator): Return
modal value. If more than one mode is found we return their average
value. Append - or + to the filter width if you rather want to
return the smallest or largest of the modal values.
(**l**) Lower: Return the minimum of all values.
(**L**) Lower: Return minimum of all positive values only.
(**u**) Upper: Return maximum of all values.
(**U**) Upper: Return maximum or all negative values only.
Upper case type **B**, **C**, **G**, **M**, **P**, **F** will use
robust filter versions: i.e., replace outliers (2.5 L1 scale off
median) with median during filtering.
In the case of **L**\ \|\ **U** it is possible that no data passes
the initial sign test; in that case the filter will return 0.0.
By default we perform low-pass filtering; append **+h** to instead
perform high-pass filtering.
Optional Arguments
------------------
.. |Add_intables| unicode:: 0x20 .. just an invisible code
.. include:: explain_intables.rst_
.. _-D:
**-D**\ *increment*
*increment* is used when series is NOT equidistantly sampled. Then
*increment* will be the abscissae resolution, i.e., all abscissae
will be rounded off to a multiple of *increment*. Alternatively,
resample data with :doc:`sample1d`.
.. _-E:
**-E**
Include Ends of time series in output. Default loses half the filter-width of data at each end.
.. _-I:
**-I**\ *ignore\_val*
To ignore values; If an input value equals *ignore\_val* it will be set to NaN.
.. _-L:
**-L**\ *lack_width*
Checks for Lack of data condition. If input data has a gap exceeding
*width* then no output will be given at that point [Default does not check Lack].
.. _-N:
**-N**\ *t_col*
Indicates which column contains the independent variable (time). The
left-most column is # 0, the right-most is # (*n_cols* - 1). [Default is 0].
.. _-Q:
**-Q**\ *q_factor*
Assess Quality of output value by checking mean weight in
convolution. Enter *q_factor* between 0 and 1. If mean weight <
*q_factor*, output is suppressed at this point [Default does not check Quality].
.. _-S:
**-S**\ *symmetry_factor*
Checks symmetry of data about window center. Enter a factor between
0 and 1. If ( (abs(n_left - n_right)) / (n_left + n_right) ) >
*factor*, then no output will be given at this point [Default does
not check Symmetry].
.. _-T:
**-T**\ *t_min/t_max/t_inc*\ [**+**]
Make evenly spaced time-steps from *t\_min* to *t_max* by *t_inc*
[Default uses input times]. Append **+** to *t_inc* if you are
specifying the number of equidistant points instead.
.. _-V:
.. |Add_-V| unicode:: 0x20 .. just an invisible code
.. include:: explain_-V.rst_
.. |Add_-bi| unicode:: 0x20 .. just an invisible code
.. include:: explain_-bi.rst_
.. |Add_-bo| replace:: [Default is same as input].
.. include:: explain_-bo.rst_
.. |Add_-d| unicode:: 0x20 .. just an invisible code
.. include:: explain_-d.rst_
.. |Add_-f| unicode:: 0x20 .. just an invisible code
.. include:: explain_-f.rst_
.. |Add_-g| unicode:: 0x20 .. just an invisible code
.. include:: explain_-g.rst_
.. |Add_-h| unicode:: 0x20 .. just an invisible code
.. include:: explain_-h.rst_
.. include:: explain_-icols.rst_
.. include:: explain_-ocols.rst_
.. include:: explain_colon.rst_
.. include:: explain_help.rst_
.. include:: explain_precision.rst_
Examples
--------
To filter the data set in the file cruise.gmtd containing evenly spaced
gravity, magnetics, topography, and distance (in m) with a 10 km
Gaussian filter, removing outliers, and output a filtered value every 2
km between 0 and 100 km:
::
gmt filter1d cruise.gmtd -T0/1.0e5/2000 -FG10000 -N3 -V > filtered_cruise.gmtd
Data along track often have uneven sampling and gaps which we do not
want to interpolate using :doc:`sample1d`. To find the median depth in a 50
km window every 25 km along the track of cruise v3312, stored in
v3312.dt, checking for gaps of 10km and asymmetry of 0.3:
::
gmt filter1d v3312.dt -FM50 -T0/100000/25 -L10 -S0.3 > v3312_filt.dt
See Also
--------
:doc:`gmt` , :doc:`sample1d` , :doc:`splitxyz`
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