NAME
gentrp - interpolate data to arbitrary sample interval
SYNOPSIS
gentrp [ -Nntap ] [ -Ootap ] [ -isii ] [ -ssio ] [ -hnso ] [
-F ] [ -S ] [ -C ] [ -CF ] [ -L ] [ -M ] [ -V ] [ -? ]
DESCRIPTION
gentrp interpolates data to an arbitrary sample interval
using one of several algorithms. The user can specifically
choose from a cubic spline interpolator, a sinc function
method, a fourier transform method or a simple linear inter-
polator. Assume for the moment that the interpolation is
from a coarser to a finer sampling. If the interpolation is
a factor of 2, 3, or 5 then the default method is the sinc
interpolator. If the interpolation is a factor of 2 the user
MAY choose from the fourier method, the cubic spline or the
linear interpolators. If the factor is NOT an integer then
cubic spline or linear interpolators are the only choice.
If the interpolation direction is from a finer to a coarser
sampling then the only choices are the fourier method (fac-
tor of 2 only), the cubic spline or the linear interpolator.
If interpolating non-seismic traces like velocity traces
then use either the cubic spline or linear interpolators.
The linear interpolator is not appropriate for seismic
datasets. It will cause a loss of high frequency informa-
tion when used to decimate data. It is mainly used on
interval velocity or non - seismic datasets.
In the past gentrp has offered no anti-alias protection.
This has been changed due to continuous user demand.
Currently a built in trapezoidal anti-alias filter [ 0 - 0 -
.90Nyquist - .98Nyquist ] is applied when specifying cubic
spline interpolation or when doing simple integer decima-
tion. To turn off this filter application use the -nopre-
filter command line option. If in doubt check the printout
file. This will allow you to prefilter your data in the
usual way using a prefilter of your own design prior to
gentrp. If the anti-alias filter is used it is reported
there along with the corner points of the filter.
gentrp gets both its data and its parameters from command
line arguments. These arguments specify the input, output,
the new sample interval in ms, the optional choice of inter-
polator, and verbose printout, if desired.
Command line arguments
-N ntap
Enter the input data set name or file immediately after
typing -N unless the input is from a pipe in which case
the -N entry must be omitted. This input file should
include the complete path name if the file resides in a
different directory. Example -N/b/vsp/dummy tells the
program to look for file 'dummy' in directory '/b/vsp'.
-O otap
Enter the output data set name or file immediately
after typing -O. This output file is not required when
piping the output to another process. The output data
set also requires the full path name (see above).
-i sii
Enter the input sample interval override. Default is
to use the value in the input line header. This param-
eter can be used to do weird interpolations (e.g. using
transp to turn records on their sides then use gentrp
to do spatial interpolation)
-s sio
Enter the output sample interval. This can be any real
value including decimals. The interpolation will be
done correctly. Remember that what gets stuffed into
the line header is an integer so that if using values
with decimal parts or values less than 1 ms it is
better to convert to micro seconds. Note also that
interpolating to small sample intervals can result in
very long trace lengths. You may have to increase the
desired sample interval or truncate the trace with an
editt. If the output sample interval is the same as
the input sample interval, the data will be passed
unchanged.
-h nso
Override sample interval in line header. Default is
integer value of sio
-C Enter the command line argument '-C' to use the cubic
spline interpolator. For noninteger resample factors
this is the only choice.
-S Enter the command line argument '-S' to use the sinc
interpolator. This is the method of choice for resample
factors that are integers, e.g. 2, 3, 4,
-n nsinc
Enter the order of the sinc interpolator. Default = 32.
Increasing this gives cleaner interpolations but at
greater cost. The default has been tested and gives
satisfactory results.
-F Enter the command line argument '-F' to use the fourier
interpolator. This is valid only for resample factors
of 2, 4, etc.
-S Enter the command line argument '-S' to use the sinc
function interpolator. This is valid only for integer
resample factors of 2, 3, 4, 5 etc.
-C Enter the command line argument '-C' to use the cubic
spline interpolator. This is valid for fractional
resample factors, e.g. 1.5, 3.14159. This is most use-
ful for interpolating non-seismic data like velocity
functions.
-CF Enter the command line argument '-CF' to use the cubic
spline interpolator with post interpolation filter.
This can alleviate some subtle problems in the high
frequency end caused by the cubic spline interpolator.
-L Enter the command line argument '-L' to use the linear
interpolator. The linear interpolator is not appropri-
ate for seismic datasets. It will cause a loss of
high frequency information when used to decimate data.
It is mainly used on interval velocity or non - seismic
datasets.
-M Enter the command line argument '-M' to convert input
sample interval to micro seconds and thereafter do
interpolation in micro secs.
-noprefilter
Enter the command line argument '-noprefilter' to turn
off anti-alias protection when decimating. This is
useful if you wish to use an anti-alias filter of your
own design as opposed to the default trapezoidal filter
installed in the program.
-V Enter the command line argument '-V' to get additional
printout.
-? Enter the command line argument '-?' to get online
help. The program terminates after the help screen is
printed.
EXAMPLES
gentrp -Nindata -Oodata -i4 -s1
where an input sample interval of 4ms is interpolated to one
of 1ms. In this case a sinc interpolator will be the
default. gentrp -Nveldata -Oodata -i16 -s8
Here a velocity data set generated at 16ms is resampled to
8ms. Because we're dealing with velocity traces a cubic
spline interpolator is the best to use.
SEE ALSO
filt
COPYRIGHT
copyright 2001, Amoco Production Company
All Rights Reserved
an affiliate of BP America Inc.
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