.. 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*\ [*modifiers*] [ |-D|\ *increment* ] [ |-E| ] [ |-L|\ *lack\_width* ] [ |-N|\ *t\_col* ] [ |-Q|\ *q\_factor* ] [ |-S|\ *symmetry\_factor* ] [ |-T|\ *t\_min/t\_max/t\_inc*\ [**+n**] ] [ |SYN_OPT-V| ] [ |SYN_OPT-b| ] [ |SYN_OPT-d| ] [ |SYN_OPT-e| ] [ |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*\ [*modifiers*] 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. By default we perform low-pass filtering; append **+h** to select high-pass filtering. Some filters allow for optional arguments and modifiers. Available convolution filter types 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 filter types 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 **+l** or **+u** if you rather want to return the lowermost or uppermost 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. 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. .. _-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 **+n** 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_-e| unicode:: 0x20 .. just an invisible code .. include:: explain_-e.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`