filter1d(1) GMT filter1d(1)

## NAME

filter1d - Do time domain filtering of 1-D data tables

## SYNOPSIS

filter1d[table]-Ftype<width>[modifiers] [-Dincrement] [-E] [-Llack_width] [-Nt_col] [-Qq_factor] [-Ssymmetry_factor] [-Tt_min/t_max/t_inc[+n] ] [-V[level] ] [-bbinary ] [-dnodata ] [-eregexp ] [-fflags ] [-ggaps ] [-hheaders ] [-iflags ] [-oflags ] [-:[i|o] ]Note:No space is allowed between the option flag and the associated arguments.

## DESCRIPTION

filter1dis 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-Noption 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.filter1dhas options-L,-Q, and-Sfor unevenly sampled data with gaps.

## REQUIRED ARGUMENTS

-Ftypewidth[modifiers] Sets the filtertype. Choose among convolution and non-convolu- tion filters. Append the filter code followed by the full filterwidthin same units as time column. By default we perform low-pass filtering; append+hto select high-pass filtering. Some filters allow for optional arguments and modifiers. Avail- able 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 ofwidthgive 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+lor+uif 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 typeB,C,G,M,P,Fwill use robust filter ver- sions: i.e., replace outliers (2.5 L1 scale off median) with median during filtering. In the case ofL|Uit is possible that no data passes the ini- tial sign test; in that case the filter will return 0.0.

## OPTIONAL ARGUMENTS

tableOne or more ASCII (or binary, see-bi[ncols][type]) data table file(s) holding a number of data columns. If no tables are given then we read from standard input.-Dincrementincrementis used when series is NOT equidistantly sampled. Thenincrementwill be the abscissae resolution, i.e., all abscissae will be rounded off to a multiple ofincrement. Alternatively, resample data with sample1d.-EInclude Ends of time series in output. Default loses half the filter-width of data at each end.-Llack_widthChecks for Lack of data condition. If input data has a gap exceedingwidththen no output will be given at that point [Default does not check Lack].-Nt_colIndicates which column contains the independent variable (time). The left-most column is # 0, the right-most is # (n_cols- 1). [Default is 0].-Qq_factorAssess Quality of output value by checking mean weight in convo- lution. Enterq_factorbetween 0 and 1. If mean weight <q_fac-tor, output is suppressed at this point [Default does not check Quality].-Ssymmetry_factorChecks 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].-Tt_min/t_max/t_inc[+] Make evenly spaced time-steps fromt_mintot_maxbyt_inc[Default uses input times]. Append+ntot_incif you are speci- fying the number of equidistant points instead.-V[level] (morea|) Select verbosity level [c].-bi[ncols][t] (morea|) Select native binary input.-bo[ncols][type] (morea|) Select native binary output. [Default is same as input].-d[i|o]nodata(morea|) Replace input columns that equalnodatawith NaN and do the reverse on output.-e[~]^<i>apattern^<i>a|-e[~]/regexp/[i] (morea|) Only accept data records that match the given pattern.-f[i|o]colinfo(morea|) Specify data types of input and/or output columns.-g[a]x|y|d|X|Y|D|[col]z[+|-]gap[u] (morea|) Determine data gaps and line breaks.-h[i|o][n][+c][+d][+rremark][+rtitle] (morea|) Skip or produce header record(s).-icols[+l][+sscale][+ooffset][,^<i>a|] (morea|) Select input columns and transformations (0 is first column).-ocols[,a|] (morea|) Select output columns (0 is first column).-:[i|o] (morea|) 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 just use-).-+or just+Print an extensive usage (help) message, including the explana- tion 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 all options, then exits.

## 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, absolute time is under the control of FOR- MAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating point val- ues are formatted according to FORMAT_FLOAT_OUT. Be aware that the for- mat in effect can lead to loss of precision in ASCII output, which can lead to various problems downstream. If you find the output is not written with enough precision, consider switching to binary output (-boif available) or specify more decimals using the FORMAT_FLOAT_OUT set- ting.

## 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 Gaus- sian 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 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

gmt(1),sample1d(1),splitxyz(1)

## COPYRIGHT

2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe 5.4.2 Jun 24, 2017 filter1d(1)

gmt5 5.4.2 - Generated Wed Jun 28 15:18:32 CDT 2017