SUMMARY

Merges (concantenates) a set of files to data in memory.

SYNTAX

MERGE {VERBOSE} {GAP ZERO|INTERP} {OVERLAP COMPARE|AVERAGE}
     {TOLERANCE_DELTA v} {filelist}

INPUT

GAP ZERO | INTERP:
	How to handle data gaps ZERO - Fill with 0.0 amplitude [default] INTERP - Interpolate, linear, within the data gap
OVERLAP COMPARE | AVERAGE:
	How to handle data overlaps COMPARE - Compare overlapping data points, exit on mismatch AVERAGE - Average overlapping data points
TOLERANCE_DELTA v:
	Tolerance between computed delta and delta reported in the header. Default tolerance is 1e-6
VERBOSE:	Describe the merge details
filelist:	A list of SAC binary data files. This list may contain simple filenames, full or relative pathnames, and wildcard characters. See the READ command for a complete description.

DESCRIPTION

The data in the files in this merge list is appended or concantenated to the data in memory. Each pair of files to be merged is checked to make sure they have the same sampling interval and station name. Any number of file, in any order are able to be merged. Data currently in memory and data identified in the merge command are merged together. If no data is specified with the merge command, data currently in memory will be merged.

TOLERANCE_DELTA

For collections of files with high sample rates, long durations or both the computation of time becomes less precise due to the limited precision of the delta value in the header.

To avoid this, a calculatd time-sampling is computed based on the difference in begin times and with sufficient precision. If the calculated time-sampling is within the tolerance specified by the TOLERANCE_DELTA, then the calculated time-sampling is used in place of the value reported in the header. Use VERBOSE for more information about the calculated and header-defined deltas:

SAC> merge verbose  ./*.SAC
  merge calculating delta
  merge calculated delta: 4.000000000000000e-03 (assuming no-gaps)
        delta in header 4.000000189989805e-03 (first file)
        difference: 1.899898e-10 = abs( calc_delta - delta )
        tolerance:  1.000000e-06
        using calulcted delta
  merging 24 files => 3600000 data points

The calculated delta assumes no gaps and no overlaps for the input files as is determined as

calc_delta = mean ( (file_{i+1}.b - file_{i}.b) / file_{i}.npts )

where the file_{i} comes before file_{i+1}.

To turn off computing the observed delta, use a value of <= 0.0

SAC r *SAC
SAC> merge verbose tol 0.0
merging 24 files => 3599999 data points
merge: Gap zero fill: [n: 899999 t: 3599.996171]
merge: Gap zero fill: [n: 1049999 t: 4199.996199]
.....

As soon as a significant gap or overlap is found between two files, all successive file boundaries will have a significant gap or overlap as the mismatch will increase with increasing n. In this data set, each file has 150000 points with a dt of 0.004s.

The output of Merge is a single file with the same name as the first file, so it was necessary to use the read statement.

EXAMPLES

To merge FILE3, FILE4, FILE1 and FILE2 into one file:

SAC> READ FILE1 FILE2
SAC> MERGE FILE3 FILE4

or:

SAC> READ FILE1 FILE2 FILE3 FILE4
SAC> MERGE

or:

SAC> DELETECHANNEL ALL
SAC> MERGE FILE1 FILE2 FILE3 FILE4

To merge files for the same station, say ELKO.Z, from four different events each stored in a separate UNIX directory:

SAC> READ data/event1/elko.z
SAC> MERGE data/event2/elko.z data/event3/elko.z data/event4/elko.z

HEADER CHANGES

NPTS, DEPMIN, DEPMAX, DEPMEN, E

ERROR MESSAGES

• 1301: No data files read in.
• 1803: No binary data files read in.
• 1307: Illegal operation on spectral file
• 1306: Illegal operation on unevenly spaced file
• 1801: Header field mismatch:
• 9005: Amplitude mismatch

WARNING MESSAGES

• 1805: Time gap (zeros added):

SEE COMMANDS

READ

LATEST REVISION

Version 102.0