SUMMARY

Defines how much of a data file is to be read.

SYNTAX

CUT {ON|OFF|pdw|SIGNAL}

INPUT

ON:	Turn cut option on but don't change pdw.
OFF:	Turn cut option off.
pdw:	Turn cut option on and change pdw. A pdw is a partial data window. It consists of a starting and a stopping value of the independent variable, usually time, which defines which part of a
file you wish to read. The most general form of this pdw is:
	ref offset ref offset
ref:	A reference value, one of the following: Z|B|E|O|A|F|N|Tn, where n=0,1...9. The meanings of these names are given below.
offset:	A positive or negative number which is added to the reference value.
SIGNAL:	Equivalent to typing: A -1 F +1.

DEFAULT VALUES

OFF

DESCRIPTION

Cut option is off. If the start or stop offset is omitted it is assumed to be zero. If the start reference value is omitted it is assumed to be Z. If the stop reference value is omitted it is assumed to be the same as the start reference value.

With the cut option off, the entire file is read. With it on, only that portion of the file between the starting and stopping cut values is read. These are values in terms of the independent variable in the data file, normally time. See the section on "Data File Structure" in the Users Manual for a discussion of dependent and independent variables. The following mnemonics are used to represent certain values of the independent variable:

B:	Disk file beginning value.
E:	Disk file ending value.
Z:	Zero.
N:	Interpret offset in terms of number of data points not independent variable. Only used for stop values.

The following mnemonics refer to reference values stored in the SAC header and are used primarily to cut time files:

O:	Event origin time.
A:	First arrival time.
F:	Signal ending time.
Tn:	User defined time picks, n = 0,1...9

The above mnemonics plus an optional positive or negative offset define either a starting or stopping value. O, A, F, and Tn can be defined for a given data file using the CHNHDR command. A and F can also be defined using the automatic picker (APK) or manual pick plot (PLOTPK) commands. If you want to select the same time window from a group of data files that have different reference times, you must use the SYNCHRONIZE command before executing the CUT and READ commands. SYNCHRONIZE modifies the headers so that each file has the same reference time. It also adjusts all of the relative times, including B and E. Then when the files are cut, they will have the same time window. Since CUT is applied to the headers on disk, you must use the WRITEHDR command after the SYNCHRONIZE command and before the READ command to get the correct results.

EXAMPLES

In these examples we assume time is the independent variable and seconds are the units:

u: B E -- Disk begin to disk end---same as turning cut off.
u: B 0 30 -- First 30 secs of the disk file.
u: A -10 30 -- From 10 secs before to 30 secs after first arrival.
u: B N 2048 --  First 2048 points of disk file.
u: 30.2 48 -- From 30.2 to 48 secs relative to disk file zero.

You can also pad the beginning or end of a file with zeros by turning on the FILLZ option in the CUTERR command, defining a cut that extends beyond the current limits of the file, and then reading the file into memory using the READ command.

SAC> r N11A.lhz SAC> lh npts

FILE: N11A.lhz - 1 npts = 3101

SAC> cuterr fillz; cut b n 4096 SAC> r SAC> lh npts

FILE: N11A.lhz - 1 npts = 4096

SAC>

ERROR MESSAGES

• 1322: Undefined starting cut for file

  • undefined reference value in the header record.
  • this error can be controlled by use of CUTERR command.
  • when this error is off, the disk begin value is used.

• 1323: Undefined stop cut for file

  • undefined reference value in the header record.
  • this error can be controlled by use of CUTERR command.
  • when this error is off, the disk end value is used.

• 1324: Start cut less than file begin for file

  • bad CUT parameters.
  • this error can be controlled by use of CUTERR command.
  • when this error is off, the disk begin value is used or zeros are insertedat the beginning of the data.

• 1325: Stop cut greater than file end for file

  • bad CUT parameters.
  • this error can be controlled by use of CUTERR command.
  • when this error is off, the disk end value is used or zeros are inserted at the end of the data.

• 1326: Start cut greater than file end for file

  • bad CUT parameters.
  • this error cannot be turned off.

  SPECIAL NOTE: Since this is a parameter-setting command, the above errors will not appear until the READ command is executed. Also, some of the above errors can be converted to warnings by the use of the CUTERR command.

LIMITATIONS

There is currently no provision for cutting unevenly-spaced files or spectral files.

SEE COMMANDS

READ, APK, PLOTPK, SYNCHRONIZE, CUTERR

LATEST REVISION

April 21, 2010 (Version 101.4)