filter1d - Time domain filtering of 1-D time series

filter1d[infile]-F<type><width>[mode] [-Dincrement] [-E] [-H[nrec] ] [-Iignore_val] [-Llack_width] [-Nn_cols/t_col] [-Qq_factor] [-Ssymmetry_factor] [-Tstart/stop/int] [-V] [-bi[s][n] ] [-bo[s][n] ] [-f[i|o]colinfo]

filter1dis a general time domain filter for multiple column time series data. The user specifies the number of columns of input and which column is the time. (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.infileMulti-column ASCII (or binary, see-b) file holding data values to be filtered.-FSets the filter type. Choose among convolution and non-convolu- tion filters. Append the filter code followed by the full filterwidthin same units as time column. Available convolution fil- ters 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 of 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 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.

-Dincrementis used when series is NOT equidistantly sampled. Thenincrementwill be the abscissae resolution, i.e., all abscissae will be rounded off to a multiple ofincrement. Alter- natively, resample data withsample1d.-EInclude Ends of time series in output. Default loses half the filter-width of data at each end.-HInput file(s) has Header record(s). Number of header records can be changed by editing your .gmtdefaults4 file. If used,GMTdefault is 1 header record. Use-Hiif only input data should have header records [Default will write out header records if the input data have them].-ITo ignore values; If an input value equalsignore_valit will be set to NaN.-LChecks 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].-NSets number of columns in input and which column contains the independent variable (time). The left-most column is # 0, the right-most is # (n_cols- 1). [Default isn_cols= 2,t_col= 0; i.e., file has t, f(t) pairs].-Qassess 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].-SChecks 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].-TMake evenly spaced timesteps fromstarttostopbyint[Default uses input times].-VSelects verbose mode, which will send progress reports to stderr [Default runs "silently"].-biSelects binary input. Appendsfor single precision [Default is double]. Appendnfor the number of columns in the binary file(s).-boSelects binary output. Appendsfor single precision [Default is double]. Appendnfor the number of columns in the binary file(s).-fSpecial formatting of input and output columns (time or geo- graphical data) Specifyi(nput) oro(utput) [Default is both input and output]. Give one or more columns (or column ranges) separated by commas. AppendT(Absolute calendar time),t(time relative to chosen TIME_EPOCH),x(longitude),y(latitude),g(geographic coordinate), orf(floating point) to each column or column range item.

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:filter1dcruise.gmtd-T0/1.0e5/2000-FG10000-N4/3-V> fil- tered_cruise.gmtd Data along track often have uneven sampling and gaps which we do not want to interpolate usingsample1d. 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:filter1dv3312.dt-FM50-T0/100000/25-L10-S0.3 > v3312_filt.dt

gmt(l),sample1d(l) GMT4.0 1 Oct 2004 FILTER1D(l)

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