Thread: how to find the value of tn marker ?

Dear Pablo -

See the list (below) of built-in numeric functions in MacSAC.
SAC2000 has all except GETVAL, I believe. You can do what you want by
using something like this example in any version of SAC:

---
funcgen seismogram
cutim ((GETTIME MAX) - (&1,DELTA / 2)) ((GETTIME MAX) + (&1,DELTA / 2))
message "Maximum value is &1,depmax& at (GETTIME MAX)"
---

Change (GETTIME MAX) to something else for another value in memory,
e.g. &1,t0&
It only works on one trace in memory, however, and destroys the memory
copy it.

---
fg seismogram
message "Only in MacSAC, max value is (GETVAL (GETTIME MAX)) at
(GETTIME MAX)"
---

It would be nice if SAC2000 implemented GETVAL; the query arises
regularly enough
to put it on the to do list.

Numeric functions
Name Num. args. Example Notes

------------------------------------------------------------------------
------
PI 0 (PI) Value of pi
ADD >0 (ADD 1 2)
SUBTRACT >0 (SUBTRACT 2 1)
MULTIPLY >0 (MULTIPLY 1 2 3 4)
DIVIDE >0 (DIVIDE 12 3)
MINIMUM >0 (MINIMUM 0.78 -3.5 15.2)
MAXIMUM >0 (MAXIMUM 0.78 -3.5 15.2)
SQRT 1 (SQRT 2) Square root
EXP 1 (EXP 2) Powers of e
ALOG 1 (ALOG 2.5) Natural logarithm
POWER 1 (POWER 3) Powers of 10
ALOG10 1 (ALOG10 1000) Base 10 logarithm
SINE 1 (SINE 0.37) Argument in radians
ARCSINE 1 (ARCSINE 0.37) Result in radians
ASINE 1 (ASINE 0.37) Synonym
COSINE 1 (COSINE 0.37) Argument in radians
ARCCOSINE 1 (ARCCOSINE 0.37) Result in radians
ACOSINE 1 (ACOSINE 0.37) Synonym
TANGENT 1 (TANGENT 0.37) Argument in radians
ARCTANGENT 1 (ARCTANGENT 1.00) Result in radians
ATANGENT 1 (ATANGENT 1.00) Synonym
INTEGER 1 (INTEGER 1.05) Integer part of expression
ABSOLUTE 1 (ABSOLUTE 1.05)
GETTIME 1,2 (GETTIME 17.05) Time of first occurrence
of
(GETTIME MAX 17.05) value in file, or value
greater
(GETTIME MIN -7.05) than (MAX) or less than
(MIN) in
(GETTIME MAX) file, or DEPMAX or DEPMIN
if no
(GETTIME MIN) value provided
GETVAL 1,3 (GETVAL 157.32) Data values of at 157.32
s in
each file in memory.
(GETVAL FILE N 157.32) Data value at 157.32 s in
file N
in memory; N integer > 0.


String functions
Name Num. args. Syntax Description

------------------------------------------------------------------------
------
CHANGE 3 (CHANGE X Y Z) Changes X to Y in Z
DELETE 2 (DELETE X Y) Deletes X in Y
BEFORE 2 (BEFORE X Y) Returns text in Y
preceding X
AFTER 2 (AFTER X Y) Returns text in Y
following X
SUBSTRING 3 (SUBSTRING X Y Z) Returns characters X to Y
in Z
Index starts with 1; X or
Y may be
END to indicate last
character
CONCATENATE - (CONCATENATE X Y Z ...) Joins all strings together

On 12 Jan 2009, at 14:23, Pablo Palacios wrote:

Dear Weitao,

I had the same necesity some time ago. I can not find a sac intruction
for solve it. In my case I was looking for the maximum value of a
spectrum. For reach it I made a csh script, the following lines are
part of that script and could be useful. If you know another easy form
to do, please tell me.

P.

# cutting the file between C1 and C2 marks and building the spectrum
file
sac<<EOF
cut $C1 $C2
r ${stn}_${cmp}_${event}.sac
chnhdr A UNDEF
chnhdr F UNDEF
dft wom a
writesp am
EOF

# smoothig the spectrum and writting it as text file
sac<<EOF
r ${stn}_${cmp}_${event}.sac.am
smooth mean h 10
write over
write alpha change .am .am.alpha
EOF

# extracting the number of point of the file to compute de maximum
frequency
sac<<EOF >! header
r ${stn}_${cmp}_${event}.sac.am
listhdr NPTS
EOF
# computing the spectrum variation between consecutive
points
set delta = `awk '/NPTS/{print 25/($3-1)}' header`
# converting the spectrum text file to spectrum column
file without header (30 first lines)
set spectrum = `echo ${stn}_${cmp}_${event}.sac.am.alpha`
awk 'NR>30{print $0}' $spectrum | awk
'BEGIN{OFS="\n"}{print $1,$2,$3,$4,$5}' > spectrum-c
# selecting the point of the maximum frequency and
computing this value
set MaxFreq = `awk '{if(NR==1){max=$1}else
if($1>max){max=$1;print NR,max}}' spectrum-c | tail -1 | awk '{print
$1}'`
set MaxFreq = `echo $delta $MaxFreq | awk '{print
$1*($2-1)}'`
# deleting temporal work files
rm -f header
rm -f ${stn}_${cmp}_${event}.sac.am.alpha
rm -f spectrum-c

# automatic picking in the spectrum file of the maximum frequency
sac<<EOF
r ${stn}_${cmp}_${event}.sac.am
chnhdr F $MaxFreq
write over
EOF

Date: Thu, 6 Nov 2008 10:37:05 -0700
From: wangwtustc<at>gmail.com
To: sac-help<at>iris.washington.edu
Subject: [SAC-HELP] how to find the value of tn marker ?

Dear All
Is there any sac command to find the value of tn marker ? I mean
if t1=100. can I find out the Y-value at that time?
thanks all.

weitao

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