We saw already that most of the Txx.H data consists of
zero values that are not very interesting for us.
Let's trim the data a bit.
The SEPlib utility
Window is used for this purpose.
If you remember,
of 1 plane of 20 traces, with 1024 samples in each trace.
In SEPlib notation,
n3=1 n2=20 n1=1024.
Let's ``zoom in'' on the interesting part of the data between
.8 seconds and offsets from the smallest (
(i.e., we will keep samples 200 through 400 of the first 10 traces).
To do its job
needs to know the number of samples and the first sample
to accept for each axis. (The defaults are ``all of them that you can''
and ``begin at the beginning'', respectively.)
For our example we would have:
Window < Txx.H n2=10 n1=200 f1=200 > Txx_Windowed.HFortunately
Windowis smart enough to understand your command using the values on the two axes too:
Window < Txx.H min1=.4 max1=.8 max2=1. > Txx_Windowed.H
We must warn you that the second method is more risky,
since it is possible that you have an error
in the sampling parameters such as
d1 in the history file, or you simply forgot
to specify them at all (so they defaulted to
You may prefer to tell
Window where to start and end
using integer sample numbers.
If you are sure that you would never make such mistakes, did you catch the
discrepancy in the two examples above?
You'll find they don't give quite the same results!
.4 and ending at
.8 is 201 samples, not 200.
As usual for computer programs,
Window does what you tell it to
do, not necessarily what you mean for it to do.
Whichever way you did it,
In Txx_Windowed.Hshows us the file
Txx_Windowed.His much reduced in size:
Txx_Windowed.H: in="/usr/local/sep/scr/joe/_Txx_Windowed.H@" expands to in="/usr/local/sep/scr/joe/_Txx_Windowed.H@" esize=4 n1=200 n2=10 n3=1 n4=1 2010 elem 8040 bytes d1=.002 d2=.1 d3=1 d4=1 o1=.4 o2=.1 o3=0 o4=0 label1=Time, seconds label2=Offset, kilometersNote in particular the new value for
Now let's have a look at what we have done:
Wiggle < Txx_Windowed.H | Tube
So far so good, but let's suppose that the journal you are submitting to
insists wiggle plots must have
traces that run down instead of across,
the order of the traces must go the other way,
and the traces must have geophysical-style shading.
No problem; from
Wiggle's self documentation
you find there are three parameters that are likely to do what you need.
Try them out:
Wiggle < Txx_Windowed.H transp=yes poly=yes yreverse=yes | TubePerhaps it would be better if the trace amplitudes were a little lower? The parameter
pclipstands for ``percentile clip''; the default is , which is meant to scale the plotting using the effective maximum absolute value while ignoring a few huge abnormal spikes. Our data is mostly zero and has no abnormal spikes, so perhaps clipping on the maximum would be more appropriate:
Wiggle < Txx_Windowed.H transp=y poly=y yreverse=y pclip=100 | Tube(Figure shows what this plot should look like.)
Wiggle < Txx\_Windowed.H par=plotpar | Pspen
Note most SEPlib programs don't care whether you type
yes'' or ``
y'' or ``
1'' or ``
0''. (Although a few old FORTRAN ones
only accept the numbers, and a few old C ones only accept the letters.)
Wiggle's self-doc you may have noticed that
Wiggle also supports parameters like ``
min1'' and ``
These will usually work just like the ones in
probably seem like the preferred way to do windowing of plots.
Unfortunately (for now at least)
Wiggle does the windowing a lazy way.
The whole plot is calculated (and plotted!) just as before,
and the graphics driver does all the work of trimming away the excess.
You can use these parameters of plot programs like
Wiggle to make
slight adjustments to the boundaries of a plot, or to make a plot smaller,
but don't use them to ``zoom in'' very far! (We'll see an example of
a legitimate use of these ``dangerous'' parameters in a few pages.)